Volkmar Dierolf Lehigh University
Yasufumi Fujiwara Osaka University
Uwe Hommerich Hampton University
Pierre Ruterana CIMAP
John Zavada North Carolina State University
D2: Nitrides I
Tuesday AM, December 02, 2008
Room 201 (Hynes)
9:30 AM - **D2.1
Development of Rare-earth Doped III-Nitride and its Application for Optoelectronic Devices.
Akihiro Wakahara 1 , Hiroshi Okada 1 Show Abstract
1 , Toyohashi University of Technology, Toyohashi Japan
10:00 AM - D2.2
The Dependence of the Luminescence Efficiency of Eu-Implanted GaN on the Implantation Fluence and Post-Annealing Temperature.
Iman Roqan 1 , Kevin O'Donnell 1 , Carol Trager-Cowan 1 , Katharina Lorenz 2 , Eduardo Alves 2 , Michal Bockowski 3 Show Abstract
1 Physics Department, SUPA, University of Strathclyde, Glasgow United Kingdom, 2 Department of Physics, Instituto Tecnologico e Nuclear, Sacavem Portugal, 3 , Institute of High Pressure Physics Polish Academy of Sciences, Warsaw Poland
Studies of implantation damage and its effects are a pre-requisite for successful implementation of ion implantation in the production of electronic and optoelectronic devices. This implantation damage affects the crystal structure and therefore the optical properties of the materials; bombardment of heavy ions (such as RE) into III-nitrides creates collision cascades and host atom displacements. This can create point defects, such as Ga and N vacancies, Ga and N interstitials, and extended defects (such as stacking faults and point defect clusters). High temperature annealing is usually necessary to remove the implantation damage and thereby activate rare earth ions optically. Previously it was shown that a thin AlN layer grown on top of GaN successfully protects the GaN surface from dissociation during high temperature annealing up to 1200 oC and a strong increase of Eu-related luminescence with annealing temperature was observed for samples implanted with a fluence of 1×1015 cm-2. We will further show in this paper that the optimum annealing temperature for optical activation increases as the implantation fluence increases, being 1000 oC and 1100 oC for 1×1013 and 1×1014 cm-2, respectively. Above the optimum temperatures, a substantial decrease in Eu3+ luminescence is observed together with the appearance of a broad yellow defect band; this band is not observed for samples implanted with higher implantation fluence of 1×1015 cm-2. Surprisingly, this broad band is not seen for GaN samples without AlN caps. In further investigations, unimplanted AlN capped and uncapped GaN samples annealed at high temperature are studied to investigate the annealing effect. The yellow band increases for AlN capped samples which indicates that new defects related to the AlN cap can suppress RE3+ luminescence in such materials. Results are compared to GaN samples annealed at 1 GPa nitrogen overpressure at temperatures up to 1400 oC without AlN cap. Optical measurements will be accompanied with Rutherford Backscattering Spectrometry (RBS) to investigate the structural properties of these films.
10:15 AM - D2.3
Optical Characterization of Nanocrystallized AlN and AlN: Er Films Prepared by Magnetron Sputtering.
Valerie Brien 1 , Syed Sajjad Hussain 1 , Hervé Rinnert 2 , Nolwenn Tranvouez 1 , Manuel Dossot 3 , Bernard Humbert 3 , Philippe Pigeat 1 Show Abstract
1 LPMIA UMR CNRS 7040, CNRS/Nancy-University, Vandœuvre-les-Nancy France, 2 LPM UMR CNRS 7556, Nancy-University/CNRS , Vandœuvre-les-Nancy France, 3 LCPME UMR 7564 CNRS, CNRS/Nancy-University, Villers-les-Nancy France
10:30 AM - **D2.4
GaN Doped with Neodymium by Plasma-Assisted Molecular Beam Epitaxy for Potential Lasing Applications.
Eric Readinger 1 , Grace Metcalfe 1 , Hongen Shen 1 , Michael Wraback 1 , Naveen Jha 2 , Nathaniel Woodward 2 , Pavel Capek 2 , Volkmar Dierolf 2 Show Abstract
1 , US Army Research Laboratory, Adelphi, Maryland, United States, 2 Physics Department, Lehigh University, Bethlehem, Pennsylvania, United States
Solid state laser applications using crystals doped with Nd are quite successful (e.g., Nd:YAG). What these crystals lack is the ability to dissipate thermal energy, with thermal conductivities on the order of 5-15 W/m-K, which limits their high power operation. By changing the matrix to a wide bandgap semiconductor such as GaN (or AlGaN), with a thermal conductivity of 100-300 W/m-K, the improvement in heat extraction could allow for major gains in solid state laser technology. It has been shown previously that rare-earth (RE) dopants such as Er, Pr, Tm, and Eu are well-suited to III-nitride semiconductors. Although there have been difficulties in preserving optical quality while achieving adequate concentrations, light emission from RE-doped GaN has been demonstrated by photoluminescence, electroluminescence, and cathodoluminescence. We provide an investigation of in situ doping of GaN with the RE element Nd by plasma assisted-molecular beam epitaxy (PA-MBE). GaN epilayers are grown on c-plane sapphire and GaN substrates and the Nd doping is controlled by an effusion cell. The ideal growth conditions for Nd incorporation in GaN are investigated and the crystal quality is verified with x-ray diffraction studies. The optical absorption characteristics are evaluated to ensure that the GaN:Nd epilayer remains transparent at the Nd emission wavelength of interest. For the highest Nd effusion cell temperatures, Rutherford backscattering and secondary ion mass spectroscopy data indicate ~5 atomic percent in epilayers grown on c-plane sapphire. X-ray diffraction found no evidence of phase segregation with up to ~1 atomic percent Nd. The highest luminescence intensities correspond to doping of ~0.5 atomic percent with the strongest emission occurring at 1.12 eV (1106 nm). We also present the Stark energy sublevels of Nd3+ ions in GaN as determined by luminescence spectra. Photoluminescence excitation spectra reveal an optimal excitation energy of 1.48 eV (836 nm). We correlate the photoluminescence spectra with transitions from the 4F3/2 excited state to the 4I9/2, 4I11/2, and 4I13/2 multiplets of the Nd3+ ion for above (325 nm) and below (836 nm) bandgap excitation. Spectral correlation of the Nd emission multiplets in addition to site-selective spectroscopy studies using combined excitation-emission spectroscopy with confocal microscopy indicate enhanced substantial doping at the Ga site. Laser structures utilizing GaN:Nd epilayers will be grown and evaluated.
11:30 AM - D2.5
Different Behavior for AlN and GaN during Medium Energy Range Rare Earth Ion Implantation and Annealing.
Pierre Ruterana 1 , Marie Pierre Chauvat 1 , Florence Gloux 1 , Katharina Lorenz 2 , Eduardo Alves 2 Show Abstract
1 CIMAP, CNRS, Caen France, 2 , Instituto Tecnológico e Nuclear, Sacavem Portugal
The damage induced in either bare GaN thin films by 300 keV rare earth ions implantation at room temperature, or through AlN epilayer capped GaN has been investigated by transmission electron microscopy (TEM) and compared with AlN thin films implanted in similar conditions. The AlN capping layer was shown to protect the GaN surface during implantation and annealing for low fluence implantation ~2x1015 at/cm2 but failed for higher fluences and temperature exceeding ~1200C. Through a 25 nm thick AlN layer, at the lowest fluence 6x1015at/cm2, the damage build-up consists in the formation of nanocrystalline pockets in GaN just below the AlN cap. AFM and TEM analysis suggest that the origin of these pockets are cracks within the AlN-capping layer. When the fluence increases to 1.2x1016at/cm2, an entirely buried nanocrystalline layer forms below the AlN cap. The AlN cap itself stays crystalline up to the highest investigated fluence of 3x1016at/cm2. When the implantation is carried out in AlN thick films, it is necessary to increase the ion fluence to more than 1017 at/cm2 in order to attain the formation of an amorphous layer. This layer forms at the ion projected range and grows by extending at the same time towards the bulk and the surface, in agreement with many materials such as silicon, but in contrast to GaN in which the highly damaged layer forms from the surface and is not amorphous, but nanocrystalline. Damage evolution during high temperature annealing will also be discussed.
11:45 AM - D2.6
Spatially Resolved Site Selective Optical Spectroscopy on Nd Doped GaN Epitaxial Layers.
Nate Woodward 1 , Naveen Jha 1 , Volkmar Dierolf 1 , Eric Readinger 2 , Grace Metcalfe 2 , Michael Wraback 2 Show Abstract
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States, 2 Sensors and Electronic Devices Directorate, U.S. Army Research Laboratory, Adelphi, Maryland, United States
Due to its favorable electronic and thermal properties GaN has been considered as a rare-earth host material for solid state laser applications. To this end, we performed spatially resolved combined excitation emission spectroscopy (CEES) on Nd ions which were in-situ-doped into GaN epitaxial films grown by plasma assisted molecular beam epitaxy (PA-MBE) on c-plane sapphire substrate. For a wide range of concentration (up to 8at%) we find in the emission a dominant incorporation site, which can be identified with good certainty as a substitutional 'Ga' site. Energy levels and electron-phonon coupling to a localized mode can be identified. The frequency of the observed mode is similar but not identical to that observed for Eu-ions in GaN. While resonant excitation yields strong emission signals even at high temperatures indicating good intrinsic quantum efficiency, above bandgap excitation of the dominant incorporation site is rather inefficient. This conclusion is further supported by the observation that in the spectra under above band-gap excitation the minority sites (with better excitation efficiencies) become more pronounced. For the majority site, confocal and NSOM imaging under selective excitation show changes in emission intensity, excitation and emission wavelength on a submicron length scale. These observations are consistent with an interpretation that the changes are due to fluctuations in Nd-concentration that will create fluctuation in the local strain fields that are caused by the substitution of the small Ga ion by a larger Nd ion (0.62Å vs 0.99Å). These results are a nice demonstration of the use of rare earth ions as probes for local perturbation. Supported by Lehigh-ARL collaborative agreement W911NF-07-2-0064 and by NSF-DMR-0705217
12:00 PM - D2.7
Luminescence and Excitation Mechanisms of Eu-doped GaN Phosphor.
Wojciech Jadwisienczak 1 , Tiju Thomas 2 , Michael Spencer 2 , Nelson Garces 3 , Evan Glaser 3 , Krzysztof Wisniewski 4 Show Abstract
1 School of EECS, Ohio University, Athens, Ohio, United States, 2 School of ECE, Cornell University, Ithaca, New York, United States, 3 Code 6877, Naval Research Laboratory, Washington, District of Columbia, United States, 4 Institute of Experimental Physics, University of Gdansk, Gdansk Poland
Applications of rare earth doped III-Nitrides are of considerable interest in different optoelectronic applications including phosphors for inorganic electroluminescent devices. In this presentation we have investigated Eu-doped GaN powder synthesized through the reaction between metals gallium, bismuth and europium in ammonia ambient . The resulting single phase powder is luminescing efficiently at 621 nm due to emission from the Eu3+ ion 5D0-7F2 transition. Temperature dependent spectroscopic studies including photo- and cathodoluminescence revealed that the emission at 621 nm is thermally quenched by one order of magnitude when ambient temperature changed from 10 K to 400 K. The excitation and quenching mechanisms responsible for the observed reduction of radiative recombination were investigated by means of photoexcitation spectroscopy (PLE), electron paramagnetic resonance (EPR) and high pressure photoluminescence (PL). It was found that Eu3+ ions are very effectively excited through excitonic recombination when excited above bandgap. Furthermore, PLE shows a possible excitation channel involving shallow donors when excited below bandgap. The presence of shallow donors was confirmed by the EPR study and their possible involvement in the energy transfer between the GaN host and Eu ion centers was studied by the high pressure PL.  C. B. Poitras, H. Wu, A. C. Turner, M. G. Spencer and M. Lipson, Appl. Phys. Lett. 89 111912 (2006).
12:15 PM - D2.8
Development of RE-Doped III-Nitride Nanomaterials for Laser Applications.
Geliang Sun 1 , Xiaofei Liu 1 , Stephen Tse 1 , Sudhir Trivedi 2 , Uwe Hommerich 3 , John Zavada 4 Show Abstract
1 Mechanical and Aerospace Engineering, Rutgers University, Piscataway, New Jersey, United States, 2 , Brimrose Corporation, Baltimore, Maryland, United States, 3 Physics, Hampton University, Hampton, Virginia, United States, 4 Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States
Conventional solid-state lasers utilize single crystal hosts, doped with rare-earth (RE) or transition metal active ion. However, key challenges in using single crystals include limited solubility of the dopant during growth, difficulties in growing large crystals, and mismatch in thermal properties. In the past decade, polycrystalline ceramic lasers, obtained by processing ceramic micropowders into bulk, have demonstrated lasing efficiencies equal to that of single crystal, e.g. Nd:YAG, while affording engineering of size and shape, as well as improving mechanical properties. By further employing nanopowders, potential exists for minimizing residual pores, sintering to near full density, enhancing thermal/mechanical properties, and increasing dopant concentration through metastable processing, thus ameliorating laser performance. Recently, III-Nitride compound semiconductors have been investigated for the development of high-power laser gain media, due to their higher thermal conductivities, hardnesses, and radiative and chemical stabilities compared to those of typical YAG.In this work, we investigate the synthesis and consolidation of GaN, AlN, and c-BN nanopowders, along with their doping using Nd, Er, and Yb. The powders are synthesized using a novel, aerodynamically-enhanced plasma process, with in-situ laser-based diagnosis of the gas-phase flow field and as-synthesized nanoparticles. Properties of the nanopowders, i.e. phase and crystallinity, morphologies and primary particle size, aggregate particle size, powder surface area, particle size distribution, and precursor conversion, are performed using X-ray diffraction (XRD), transmission electron microscopy (TEM), dynamic light scattering (DLS), Brunauer-Emmet-Teller (BET), nano-scanning mobility particle sizer (nano-SMPS), and thermogravimetric analysis (TGA). Cases where RE is doped directly during the plasma synthesis process and where undoped powders are post-treated with dopant exposure and nitridization are investigated and compared. Nanocomposite pellets are fabricated from the RE-doped III-Nitride nanopowders, and the technical pathway for producing such bulk ceramics is examined. Finally, both powders and ceramic pellets are characterized spectroscopically. Photoluminescence of the powders and absorption/emission characteristics and emission life times of the pellets are measured.
12:30 PM - **D2.9
Rare Earth Activated GaN Luminescent Powders by Combustion Synthesis and GaN:RE Thin Films Deposited by a Novel Hybrid PLD/MOCVD Technique.
Gustavo Hirata 1 Show Abstract
1 Center of Nanoscience and Nanotechnology, National University of Mexico, San Ysidro, California, United States
In this work we report on the fabrication and optical properties of rare earth-activated gallium nitride (GaN) luminescent powders and thin films. GaN and GaN:RE (RE=Eu,Tb) powders with excellent photoluminescent and cathodoluminescent properties were prepared via a low-temperature combustion synthesis method. These powders were pressed into 2 cm diameter targets for laser ablation experiments.On the other hand, a novel low-temperature method was developed by combining pulsed laser ablation and metal-organic chemical vapor deposition (MOCVD) in order to fabricate GaN thin films activated with rare earth (RE) ions. Laser ablation is used to remove material from the GaN target and, simultaneously europium atoms are injected from a MOCVD bubbler into the laser ablation plume and sprayed onto the film growth surface to form GaN:RE (RE=Eu,Tb) luminescent thin films. The films were deposited on GaN/Al2O3 substrates. The X-ray diffraction analysis of these GaN:RE samples showed that the films have the hexagonal phase of GaN and are polycrystalline with strong texture along the  direction. Cathodoluminescent measurements acquired at room temperature showed the band-edge emission of GaN and the corresponding red or green emission originated within the intra-shell transitions of either Eu3+ or Tb3+. The europium-doped GaN:Eu3+ thin films showed strong luminescence due to f-f transition lines within the Eu3+ (4f6) electron emission configuration. The largest peak emission line at around λ= 621 nm, is assigned to the hypersensitive 5D0→7F2 transition using a forced electric dipole transition mechanism. Furthermore, from the analysis of the luminescence spectra which are revealed by the local environment of the Eu3+, it is established that europium ions occupy low-symmetry sites. Lack of inversion symmetry at the cationic sites is favorable for observing the electric dipole transition as a forced transition due to the admixture of the odd parity states. For GaN:Tb3+ thin films various transitions originated from the 5D4 level of Tb3+ are observed including the classical green transition to the 7F5 level. These transitions were observed in GaN:Tb3+ powders, with the exception of the near-band-edge (NBE) at λ= 370 nm. This indicates that the lower defect level in the films improves the quality of the material.We have demonstrated that combining two techniques: pulsed laser deposition and MOCVD represent a novel approach for the synthesis of RE-activated GaN luminescent thin films.
D3: Nitrides II
Tuesday PM, December 02, 2008
Room 201 (Hynes)
2:30 PM - **D3.1
Ferromagnetism and Luminescence of Diluted Magnetic Semiconductors GaGdN and AlGdN.
Shuichi Emura 1 , Masahiro Takahashi 1 , Hiroyuki Tambo 1 , Tetsuya Nakamura 2 , Y. Zhou 1 , Shigehiko Hasegawa 1 , Hajime Asahi 1 Show Abstract
1 The Institute of Scientific and Industrial Research, Osaka University, Ibaraki, Osaka, Japan, 2 , JASRI/SPring-8, Sayocho, Hyogo, Japan
Rare earths are well known as luminescent centers and as principal component of ferromagnetic materials. Research on the luminescent nature of these elements and their compounds is of a long history of over half century in modern science, and also development of new ferromagnetic materials containing rare earth elements as main carriers has old history over one century. As our society gets more and more complicated, multi-functional materials are expected to be invented to meet the needs of the infrastructure in the near future. Ga(Al)N based diluted magnetic semiconductors, for example GaGdN, show luminescence and room-temperature ferromagnetism . Therefore, these are one of the high potential materials for near future devices. GaGdN has unusual ferromagnetic behaviors. Even in very dilute Gd concentration (7x1015/cm3), it shows the ferromagnetic behavior at room temperature , and takes the second magnetic phase at 10 - 20K. Moreover, curious step-like temperature dependence in soft X--ray magnetic circular dichroism (SX-MCD) spectra is observed around 30 – 70K. GaGdN seems to show three different magnetic phases. With the aid of SX-MCD spectra along with X-ray absorption fine structure analysis, the unique ferromagnetism in GaGdN will be discussed. On the other hand, we found a luminescence at 652 nm in GaGdN. Gd center in the trivalent state usually presents a sharp luminescence around 318 nm (f – f transition), which corresponds to the transition to the lowest excited energy level in multiplet of f7 electron configuration, and is observable in AlGdN because the band gap of AlN (about 6eV) is beyond the luminescent energy. We present a model on the origin of the luminescent center. Application to devices combining the magnetic and luminescence properties of GaGdN will be proposed. Teraguchi et al., Solid state comm. 122 (2002) 65.  S.Dhar et al., Phys. Rev. Letters, 94 (2005) 037205-1,
3:00 PM - D3.2
First Principles Calculations for Gd doped GaN.
Chandrima Mitra 1 , Walter R.L Lambrecht 1 Show Abstract
1 Physics , Case Western Reserve University, Cleveland, Ohio, United States
3:15 PM - D3.3
Magnetotransport in Gd-implanted Wurtzite GaN/AlxGa1-xN High Electron Mobility Transistor Structures.
Fang-Yuh Lo 1 2 , Alexander Melnikov 2 , Dirk Reuter 2 , Yvon Cordier 3 , Andreas Wieck 2 3 Show Abstract
1 Department of Physics, National Dong-Hwa University, Hualien Taiwan, 2 Lehrstuhl für Angewandte Festkörperphysik, Ruhr-Universität Bochum, Bochum Germany, 3 Centre de Recherche sur l'Hétéro-Epitaxie et ses Applications, Centre National de la Recherche Scientifique, Valbonne France
GaN/AlxGa1-xN high electron mobility transistor (HEMT) structures grown by ammonia-source molecular beam epitaxy (MBE) are focused-ion-beam implanted with 300 keV Gd-ions at room temperature. The two-dimensional electron gas (2DEG) of these HEMT structures is located 27 nm underneath the sample surface. At 4.2 K, current-voltage characteristics across implanted rectangles show that the structures remain conducting up to a Gd-dose of 1×1012 cm-2. Anomalous Hall effect (AHE) and anisotropic magnetoresistance (AMR) are observed at T = 4.2 K for structures implanted with different doses of Gd. Measurements of AHE in the wide temperature range from 2.4 K to 300 K show that the magnetic ordering temperature of these structures is around 150 K. Therefore, these Gd-implanted HEMT structures containing the still conducting 2DEG, which is now embedded in a ferromagnetic semiconductor, open the possibility to polarize the electron spins. The support by the Deutsche Forschungsgemeinschaft in the framework of the Sonderforschungsbereich SFB 491 and the Schwerpunktprogramm Halbleiterspintronik SPP 1285, and by the Université Franco-Allemande (DFH/UFA) within the CDFA-05-06 are gratefully acknowledged.
3:30 PM - D3.4
Rare Earth Doping of GaN with Gadolinium by MOCVD.
Shalini Gupta 1 , Andrew Melton 1 , William Fenwick 1 , Hongbo Yu 1 , Ian Ferguson 1 2 Show Abstract
1 Electrical and Computer Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States, 2 Materials Science and Engineering, Georgia Institute of Technology, Atlanta, Georgia, United States
Rare earth (RE) elements can be used as dopants for spintronics applications. Instead of relying on the d-shells of the transition metal (TM) as the magnetic element, the f-electrons from the RE elements are used. Despite the promising results obtained by molecular beam epitaxy for Ga1-xGdxN, till date there are no metal organic chemical vapor deposition (MOCVD) reports on Ga1-xGdxN. This paper presents the first report on MOCVD doping of GaN with gadolinium (Gd). Ga1-xGdxN thin films (x = 0-24%, calculated per molar flow) were grown using the precursor Tris(2,2,6,6-tetramethyl-3,5-heptanedionato) gadolinium (III); all growths were carried out on 2” sapphire substrates under typical GaN temperatures and pressures. The growth rate was maintained at 0.2 µm/hr to allow enough time for adatom diffusion and to prevent clustering. Although Gd is a large atom, X-ray diffraction (XRD) measurements did not show any shift in the GaN peak or the presence of any gross secondary phase. Co-doping with silane and magnesium did not cause any change in the XRD peaks either. Furthermore, atomic force microscopy (AFM) measurements revealed smooth Ga1-xGdxN films with topography similar to that of GaN. Hall measurements showed that the Ga1-xGdxN has typical n-GaN background carrier concentration and that this carrier concentration can be increased by silane co-doping (1016 cm-3 to 1018 cm-3). Magnesium co-doping of 1019 cm-3 results in a decrease in carrier concentration (measured: 1015 cm-3) and thereby increases the resistivity, making it hard to get reliable hall measurements. These films are optically active and photoluminescence measurements on Ga1-xGdxN showed, in addition to the GaN peak, the presence of peaks in the range of 3.1 eV-3.3 eV which can be attributed to the internal transition associated with Gd3+. Moreover, a peak is seen at 1.74 eV which could possibly be attributed to Gd3+. Room temperature magnetization data for Ga1-xGdxN showed that as the Gd concentration is increased, a transition from diamagnetism to ferromagnetism occurs, and a magnetization strength of 20 emu/cm3 is obtained for ~12% Gd. Moreover, co-doping with silane and magnesium results in an increase in magnetization strength, with the maximum magnetization obtained for the p-type Ga1-xGdxN (~500 emu/cm3 for x = 12 %, and p-doping of 1019 cm-3). It is interesting to note that the magnetization strength can be enhanced by co-doping and provides the possibility that the mechanism associated with the observed ferromagnetism could be due to carrier mediated ferromagnetism. This is the first MOCVD report on Ga1-xGdxN, and the results obtained are promising, as a large magnetic signal is obtained for conducting Ga1-xGdxN films which could prove to be a beneficial dilute magnetic semiconductor for spintronic applications.
4:00 PM - **D3.5
Gd-doped III-nitride Dilute Magnetic Semiconductor Materials.
Ryan Davies 1 , Jennifer Hite 1 , Rachel Frazier 1 , Brent Gila 1 , Gerald Thaler 1 , Cammy Abernathy 1 , Stephen Pearton 1 , Christopher Stanton 2 , John Zavada 3 Show Abstract
1 Materials Science & Engineering, University of Florida, Gainesville, Florida, United States, 2 Physics, University of Florida, Gainesville, Florida, United States, 3 Electronics Division, U.S. Army Research Office, Durham, North Carolina, United States
Wide band gap dilute magnetic semiconductor (DMS) materials are being investigated as potential materials for spintronic devices. Since these materials demonstrate magnetic behavior at room temperature in addition to their semiconducting characteristics, they possess the potential for larger integration density, less power consumption than their electronic counterparts, and room temperature generation of polarized optical signals. Gd-doped III-nitrides are particularly interesting due to the low Gd concentrations needed to achieve ferromagnetic ordering at room temperature and to the large magnetic moments obtained in this system. However, one area of concern with these materials is the apparent absence of magneto-optical effects at room temperature. Although the Kerr effect has been demonstrated for magnetic dopants in the smaller band gap arsenides, this has not been the case for the larger band gap nitrides. This along with the absence of an anomalous Hall effect at room temperature raises questions regarding the source of the observed magnetic ordering. Various models have been proposed suggesting defect involvement and experimental evidence is beginning to point in this direction as well. This talk will review the current understanding of the role of co-dopants, growth conditions, processing and post-growth irradiation in the context of elucidating the ordering mechanism. Comparison with similar effects in GaMnN will also be presented. Finally, implications of the ordering mechanism on future device development will be discussed.
4:30 PM - D3.6
Ultraviolet Luminescence from Thullium-doped Aluminum Gallium Nitride Epilayers.
Neeraj Nepal 1 , John Zavada 1 , Ei Ei Brown 2 , Uwe Hommerich 2 , Ashok Sedhain 3 , Jingyu Lin 3 , Hongxing Jiang 3 , Dong Lee 4 , Andrew Steckl 4 Show Abstract
1 ECE, North Carolina State Univ, Raleigh, North Carolina, United States, 2 Physics, Hampton University, Hampton, Virginia, United States, 3 Physics, Kansas State University, Manhattan, Kansas, United States, 4 ECE, University of Cincinnati, Cincinnati, Ohio, United States
Incorporation of rare-earth (RE) atoms into a semiconductor host has received wide spread attention due to potential optoelectronic applications including displays, optical amplifiers, and light-emitting devices. Thulium is an important RE element for such applications since in its trivalent charge state (Tm3+) prominent luminescence in the visible and infrared regions has been observed in glass fibers. In this paper we report on ultraviolet (UV) luminescence found in AlGaN epilayers grown by solid-source molecular beam epitaxy. The UV luminescence appears only if the bandgap of the AlGaN layer exceeds the photon energy of the corresponding 4f shell transition. Using above band gap optical excitation prominent, narrow emission lines, at 298 and 358 nm, were observed in epilayers with high Al content. With below band gap excitation broad emission bands were found at these wavelengths. Temperature dependence and lifetimes of the UV emissions have been measured. The data indicate the presence a defect level related to the Tm incorporation and a model is presented to explain the UV properties.
4:45 PM - D3.7
Europium Doping of Cubic (Zincblende) GaN by Ion Implantation.
Katharina Lorenz 1 2 , N. Franco 1 2 , E. Alves 1 2 , I. Roqan 3 , K. O'Donnell 3 , C. Trager-Cowan 3 , R. Martin 3 , D. As 4 , M. Panfilova 4 Show Abstract
1 UFA, Instituto Tecnologico e Nuclear, Sacavem Portugal, 2 CFNUL, University of Lisbon, Lisbon Portugal, 3 Department of Physics, SUPA, University of Strathclyde, Glasgow United Kingdom, 4 Department of Physics, University of Paderborn, Paderborn Germany
Eu-doped wurtzite GaN (W-GaN) has been widely studied due to its intense red light emission at ~ 621 nm in epitaxial films or powders. Ion implantation is a useful technique to achieve the incorporation of optically active rare earth dopants into pre-grown W-GaN templates. On the other hand very few reports exist on rare earth doping of cubic (zincblende) GaN (ZB-GaN) and on ion implantation in this material. In this study Eu was implanted at different fluences between 1013 and 1015 at/cm2 into ZB-GaN layers grown by Molecular Beam Epitaxy (MBE). Detailed structural characterization before and after implantation was performed by X-ray diffraction (XRD) and Rutherford Backscattering/Channeling (RBS/C) spectrometry. RBS/C spectra of the as grown templates reveal a relatively strong dechannelling with depth probably caused by wurtzite phase inclusions. XRD pole figures confirm that the as-grown samples contain wurtzite phase inclusions whose <001> plane is aligned with the <111> plane of the cubic lattice. Implantation causes an expansion of the lattice parameter in the implanted region similar to that observed for W-GaN. While implantation in W-GaN causes the formation of a highly damaged nano-crystalline surface layer, this surface damage is absent in implanted ZB-GaN. By thermal annealing the bulk implantation damage in ZB-GaN could partly be removed, however, an increase of the wurtzite phase fraction was observed at the same time. Although the photoluminescence (PL) emission is dominated by luminescence from Eu ions incorporated into the W-GaN fraction, selective PL and PL excitation spectroscopy revealed several additional emission lines, which may be attributed to Eu-related optical centers in ZB-GaN.
5:00 PM - D3.8
Current-injected 1.54 μm Emitters based on Er Doped GaN.
Rajendra Dahal 1 , Cris Ugolini 1 , Ashok Sedhain 1 , John Zavada 2 , Jingyu Lin 3 , Hongxing Jiang 3 Show Abstract
1 Physics, Kansas State University, Manhattan, Kansas, United States, 2 Electrical & Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 3 Nano Tech Center and Electrical and Computer Engineering, Texas Tech University, Lubbock, Texas, United States
Rare earth elements, in particular erbium (Er) doped III-nitride semiconductors has been widely explored aiming to achieve photonic devices with multiple functionalities in photonic integrated circuits which are not possible with either Er doped silica glasses or narrow band gap semiconductors like InGaAsP. Emitters and optical amplifiers operating at 1.54 μm based on Er doped semiconductors are expected to be electrically pumped, integratable, temperature insensitive and high signal gain with low noise. These properties are very attractive for next generation optical network system where multiple amplification steps are required. We will report here on the fabrication of a chip size current injected 1.54 μm emitters by heterogeneously integrating metal organic chemical vapor deposition (MOCVD) grown Er doped GaN with 365 nm nitride light-emitting diodes. The emitted intensity at 1.54 μm varied almost linearly with input forward current. Further, the propagation loss at 1.54 μm of Er doped GaN waveguide amplifier will also be discussed. The feasibility of electrically pumped optical amplifiers for photonic integrated circuit with advantages of both semiconductor optical amplifiers and Er-doped fiber amplifiers will also be discussed.
5:15 PM - D3.9
Excitation Pathways of Rare Earth Ions by Energetic Electrons.
Samson Tafon Penn 1 , Zackery Fleischman 1 , Leon Maurer 1 , Volkmar Dierolf 1 Show Abstract
1 Physics, Lehigh University, Bethlehem, Pennsylvania, United States
The announcement of efficient electrically pumped luminescence of rare earth ions that are placed in the insulating layer of a MOS-type Si/SiO2 structure renewed the quest for a silicon-based light source . Similarly, electrically pumped rare earth emission and optical amplification have been found in rare earth doped wide bandgap semiconductors such as GaN[ 2]. For both cases, the energy transfer from the energetic electrons determines the critical limit of the device performance. We report on our comprehensive study of the electronic excitation pathways of rare earth ions in GaN, AlGaN, AlN, and LiNbO3. In order to simulate the electron injection in real devices, we used the electron beam within an electron microscope and probed the resulting cathodoluminescence. Manipulating the electron beam in terms of acceleration voltage, beam current, position, and sweep frequency allows studying the saturation behavior of the emission. We find that in many cases the saturation occurs for smaller beam currents than predicted from our photoluminescence studies on the same samples. Moreover, the typical time constants do not always reflect the lifetime of the involved rare earth ion transition indicating the presence of an intermediate step that can act as a bottleneck depending on the lifetime of such a (defect) trap and the efficiency of energy transfer to the rare earth ion. We find in LiNbO3 doped with Er, Eu, and Pr an intermediate trap state that has an effective lifetime in the order of 200µs and a rather low energy transfer rate. resulting in a very weak cathodoluminescence signal. We speculate that after the electronic excitation of the host material, polarons are formed through self-trapping and will constitute the trap state. The excitation pathways are significantly more efficient in the wide bandgap semiconductor hosts but a clear dependence on the incorporation site is observed by site-selective studies. In these hosts, we speculate that N-defects may act as the trap. In both classes of material we come to the conclusion that a direct excitation of the RE earth through either the direct impact or through free excitons is very inefficient. The presence of defects is needed to allow efficient electrically pumped rare earth emission!!. This important conclusion of our work may explain the inverse relation of device efficiency to its lifetime reported by Coffa et al. in the Si/SiO2 device structures .  M.E. Catagna, S. Coffa, M. Monaco, A. Muscara, L. Caristia, S. LOrenzi, and A. Messina, Mat. Sci&Eng B 105, 83 (2003) A.J. Steckl, J. Heikenfeld, D. Lee, M. Carter, C. Baker, Y. Wang, and R. Jones, IEEE Journal on Selected Topics n Quantum Electronics 8, 749 (2002).Supported by NSF-grant DMR-0602986, NSF-DMR-0705217, and collaborative agreement W911NF-07-2-0064 between the Army Research Lab and Lehigh University
5:30 PM - **D3.10
Optical Activation of Rare Earths Implanted into III-Nitrides.
Eduardo Alves 1 , Katharina Lorenz 1 , F. Gloux 2 , P. Ruterana 2 , Alan Braud 2 , Kevin Donnell 3 , Robert Martin 3 Show Abstract
1 Physics and Accelerators, ITN, Sacavem Portugal, 2 , CIMAP, UMR 6252 ENSICAEN-CNRS-CEA-UCBN, Caen France, 3 Department of Physics, SUPA, University of Strathclyde, Glasgow United Kingdom
Wide band-gap semiconductors, particularly III-nitrides, have become one of the most studied materials during the last decades. These compounds are the base of a new generation of optoelectronic devices operating in the UV-Blue region of the electromagnetic spectrum. Incorporation of rare-earth (RE) into nitrides creates new routes to build novel all-nitride electroluminescent devices, using the sharp intra 4f transitions of these elements. The introduction of the RE ions in the nitride lattice during the growth or by ion implantation creates defects which influence the behaviour of the optical active region.In this work we present our recent achievements on rare earth (RE) doped III-nitrides by ion implantation. A combination of techniques (Rutherford backscattering/Channeling, High Resolution X-Ray Diffraction and Electron microscopy, EXAFS, Photoluminescence and Cathodoluminescence) were used to assess the mechanism responsible for the optical and structural behaviour of the doped materials. The data clearly demonstrate how the optical activity of the RE could be enhanced by orders of magnitude by reducing the number of non-radiative paths related with defects and by the incorporation of RE ions into substitutional Ga lattice sites. The results suggest a correlation between the increase of substitutional RE ions and the Cathodoluminescence intensity.
D4: Poster Session
Wednesday AM, December 03, 2008
Exhibition Hall D (Hynes)
9:00 PM - D4.1
Luminescence Enhancement in Eu-doped GaN Powder by Oxidative Passivationof the Surface.
Tiju Thomas 1 , Mvs Chandrashekhar 1 , Carl Poitras 1 , Junxia Shi 1 , Jesse Reiherzer 2 , Francis DiSalvo 2 , Michal Lipson 1 , Michael Spencer 1 Show Abstract
1 School of Electrical and Computer Engineering, Cornell University, Ithaca, New York, United States, 2 Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York, United States
We show a method to increase the red luminescence of Eu doped GaN(GaN:Eu) powder by a factor of >3 using a nitric acid rinse, over powderreported previously in literature. The mechanism of this enhancement wasstudied using XPS, XRD and PL. The powder was synthesized using a lowcost, high yield rapid-ammonothermal process reported in literature. Theresulting powder is known to have a strong emission in the red. Despiteits strong luminescence. the powder prepared using this method is alsofound to be dark on account of several impurities in it. The dark color ofthe powder can be attributed to Europium Nitride, elemental Bi and Ga, asdetermined by XRD analysis. Due to its dark color, these impurities arestrongly absorbing, decreasing the luminescence of the GaN:Eu.These impurities were removed using a simple chemical rinse in an acidsolution. While the chemical rinse clears the powder of all theimpurities, we also observed that it enhances the photoluminescence of thepowder. Nitric acid, hydrochloric acid rinses of varying times andtemperatures were investigated.The XPS peak correponding to Ga showed achemical shift, indicating a Ga-O bond. This peak shifted continously withrespect to the duration over which the chemical rinse was performed beforereverting back to its unshifted position. This observation suggests thatour process continuously oxidizes the GaN surface, forming a GaN-oxideinterface. This additional shift is attributed to electrostatic potentialsat the interface arising from the valence band discontinuity betweenGaN/Ga2O3, in analogy with GaN/AlN interfaces reported earlier by Markoc et al. A valenceband offset of ~1 eV was estimated, in good agreement with known band parameters.As the oxide layer gets formed uniformly around the GaN particle, greater interface potentials develop, owing to the fact that pure Ga2O3 has alarger bandgap than GaN. We have found that a well defined GaN-oxideinterface was formed by rinsing in nitric acid for 4 hours at roomtemperature. The valence band offset attains the ideal GaN/Ga2O3 valuewhen the PL intensity of the powder is highest. We suggest that the higherintensities of Ga2O3 passivated GaN:Eu is because the surface states thatmight be responsible for reducing the luminiscence of these GaN particlesare eliminated when a clean GaN-oxide junction is formed. We alsospeculate that the removal of absorbing impurities in the as preparedpowder contributes to this increase. If the rinse is too short, theluminescence is not maximized due to incomplete oxide formation andimpurity removal. However, if the chemical rinse is performed for toolong, all the GaN gets consumed, quenching the luminiscence. Thisquenching is accompanied by a corresponding loss of interface potential,as observed by XPS.
9:00 PM - D4.10
Luminescence Properties from Si- and Ge-doped AlN:Eu Thin Films Prepared by RF Magnetoron Sputtering.
Naoki Iwata 1 , Shin-ichiro Uekusa 1 Show Abstract
1 School of Science and Technology, Meiji University, Kawasaki-shi Japan
The inorganic EL display are attracting significant attention as one of the most promising flat panel displays. The displays are low power consumption. Moreover, there is a feature that it is a high contrast because it emits spontaneously light. Recently the main of the research and development of inorganic EL is a sulfureted system. However, the sulfide is chemically unstable in wet atmosphere. Moreover, it has a negative environmental impact given as a problem. Then, we paid attention to AlN in stead of sulfide, because AlN have been studied as promising materials for light emitting diodes and EL devices, it has a wide band gap (6.2 eV), high thermal conductivity, and chemical inertness. Inorganic EL of nitride fluorescent body is few report. In the case of AlN thin films doped with Eu, red line emission is usually seen as a result of electron transition of Eu3+. Recently, it is reported to show blue luminescence from AlN:Eu powder that adds Si powder. The aim of this study is to obtain the strong blue luminescence from the Si doped AlN:Eu thin films comparison with Ge doped AlN:Eu thin films. To remove the surface oxidation of the n-Si(111) it was etched 5 % by using HF, subsequently loaded in the growth chamber for sputtering. The Eu chips (99.9 %) on the Al target (99.999 %) and several Si chips (99.9 %) were used, and Si doped AlN:Eu thin film were deposited. Moreover the Eu chips (99.9 %) on the Al target (99.999 %) and several Ge chips (99.9 %) were used, and Ge doped AlN:Eu thin film were deposited. Nitrogen and Argon gas were used for the preparing the sample. The prepared samples were annealed in the temperature range from 400 to 900oC for 30 minutes and 60 minutes for in the nitrogen and oxygen atmosphere. The luminescence of the samples was measured by a photoluminescent (PL). The Eu addition density of the sample was measured by Energy dispersive X-ray profile (EDX). Crystallinity of the samples was measured by X-ray diffraction (XRD). The thin films were prepared in the flowing quantity of N2 and Ar was 5.6 sccm and 2.4 sccm, respectively. Two main peaks were observed in PL spectra features. One main peak was observed around 530 nm, and an increase in the luminescence intensity was seen by increasing the annealing temperature up to 900oC. It has shifted to the short wavelength side. The result luminescence from Eu2+ in AlN:Eu thin film. The other main peak was observed at about 620 nm. This means luminescence from Eu3+. We systematically discuss the results in detail.
9:00 PM - D4.11
Optical and Luminescent Properties of Highly Oriented Nanocrystalline Gd2-xEuxO3 Thin Films.
Segundo Jauregui-Rosas 1 2 , Oscar Perales-Perez 3 , Maharaj Tomar 2 , Omar Vasquez 2 Show Abstract
1 Fisica, Universidad Nacional de Trujillo, Trujillo Peru, 2 Physics, University of Puerto Rico at Mayagüez, Raleigh, North Carolina, United States, 3 Department of Engineering Science and Materials, University of Puerto Rico at Mayagüez, Mayagüez, Puerto Rico, United States
Highly crystalline and transparent Eu-doped Gd2O3 thin films were produced by sol-gel method and spin coating process from starting acetic acid solutions with no need for any chelating agent. The effect of the atomic fraction of Eu3+ ions (‘x’ =0.05-0.30) on the structural, optical and luminescent properties has been determined. It was found that the oxide films exhibited a preferential growth along the (400) plane. No other than cubic phase was developed at all levels of dopant. UV-vis measurements revealed the high transparency of the films in the visible region and evidenced a negligible effect of Eu contents on the corresponding band gap value (5.3eV). It was also found that the luminescence properties were strongly dependent on both the excitation wavelength and europium content; the most efficient excitation conducive to red luminescence was achieved at the absorption band of the Gd2O3 host (229nm). Under this condition, all films exhibited strong red emission characteristic of the Eu3+ ions hosted by crystalline frameworks. The emission intensity was strongly dependent on the Eu content; the most intense luminescence was obtained for x=0.15. The drop in the luminescence intensity for ‘x’ values higher than 0.15 was attributed to the quenching concentration effect. Similar behavior was observed using the charge transfer band as excitation wavelength. Morphological and film roughness analyses of films using Atomic Force Microscopy (AFM) will also be presented and discussed.
9:00 PM - D4.12
Studies of III-Nitride Superlattice Structures and its Deformation upon Implantation with Lanthanide Ions.
Mohammad Ebdah 1 , W. Jadwisienczak 2 , H. Morkoc 3 , A. Anders 4 Show Abstract
1 Department of Physics and Astronomy, Ohio University, Athens, Ohio, United States, 2 School of Electrical Engineering and Computer Science, Ohio University, Athens, Ohio, United States, 3 Department of Electrical Engineering and Physics Department, Virginia Commonwealth University, Richmond, Virginia, United States, 4 , Lawrence Berkeley National Laboratory, Berkeley, California, United States
Rare earth (RE) ions doped low dimensional III-Nitride structures including quantum wells (QW), superlattices (SL) and quantum dots (QD) have received recently increasing interest due to their potential applications in optoelectronics. In this work, AlN/GaN SLs of 20 periods with a fixed well/barrier thickness ratio were grown by chemical vapor deposition (CVD) technique on GaN/(0001) sapphire substrate without a capping layer on top. Implantation of selected rare earth ions was done at 150 keV and a dose of up to 1x1015 cm-2 at room temperature. Samples were given post implant isochronal thermal annealing treatment in 800 – 1200°C temperature range in NH3 and N2 using a conventional resistive furnace and rapid thermal annealing technique. The interfacial deformation between the SL layers before and after implantiation, as well upon annealing, has been investigated by X-ray diffraction (XRD) and the characteristic satellite peaks of SLs were measured for the (0002) reflection up to the second order in the symmetric Bragg reflections. Furthermore, the optical properties of RE ions implanted AlN/GaN SLs have been studied by means of ellipsometry, photo- and cathodoluminescence and photoluminescence excitation spectroscopy. The luminescence results demonstrate an increase of the radiative emission efficiency from RE-doped AlN/GaN SL when compared with RE-doped III-Nitride thin films. Furthermore, the possibility of using RE ions confined in III-Nitride low-dimensional quantum structures for optoelectronics devices is considered.
9:00 PM - D4.13
Similarities and Differences of Sensitization Mechanism of Er3+ in Si-rich SiO2 with and without Silicon Nanocrystals.
Oleksandr Savchyn 1 , Pieter Kik 1 , Ravi Todi 2 , Kevin Coffey 2 Show Abstract
1 CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States, 2 AMPAC, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States
The indirect excitation of erbium in silicon-rich SiO2 has long been associated with the presence of silicon nanocrystals formed inside the silica matrix. However our recent studies showed that excess-silicon related luminescence centers (LC) are in fact the dominant source of Er3+ excitation in this material. The current study demonstrates that a significant fraction of the LC-mediated erbium excitation occurs directly into the first excited state with a LC-Er transfer time < 40 ns. This fast excitation process could allow for luminescence-center-sensitized Er3+ doped gain media with high maximum output power. Erbium-doped (0.63 at.%) Si-rich SiO2 films (Si excess 12 at.%) were prepared using sputter deposition technique. The subsequent annealing at different temperatures resulted in films with significantly different microstructure, namely (a) samples that do not contain detectable Si nanocrystals (annealed at 600oC), and (b) samples containing silicon nanocrystals (annealed at 1100oC). Modulated continuous-wave excitation at a wavelength of 351 nm was used to determine the effective absorption cross-section of the first excited state of Er3+ at sample temperatures in the range 15 – 300K. The obtained Er3+ absorption cross section was found to be approximately ~(0.9 - 1.0) x 10-15 cm2 for samples with and without silicon nanocrystals, and remained relatively constant in the considered temperature range. In contrast, the absorption cross section of Si nanocrystals is found to increase by a factor of ~ 2 as the temperature is increased from 15K to 300K. These results support the conclusion that Si-nanocrystal-mediated sensitization is not the dominant Er3+ excitation mechanism. Temperature dependent pulsed excitation measurements were conducted at an excitation wavelength of 355 nm. Under these conditions, samples not containing Si nanocrystals clearly show the presence of two different processes leading to the excitation of Er3+ ions into the first excited state: a fast luminescence center mediated excitation directly into the first excited state (τtransfer, fast < 40 ns), and a relatively slow excitation with a transfer time approximately equal to the 4I11/2 lifetime (τtransfer, slow ≈ 3 μs). The clear correlation of the excitation time constant and the lifetime of the Er3+ second excited state suggests that the slow Er3+ excitation process in low-temperature processed samples is related to the spontaneous relaxation from the 4I11/2 level into the 4I13/2 level. Based on the temperature-dependent magnitude of these two contributions and the measured time constants, the temperature dependence of the branching ratio of the second excited state is derived. The excitation processes of Er3+ in the samples with and without silicon nanocrystals are compared and the importance of these findings for the development of silicon compatible Er-based light sources is discussed.
9:00 PM - D4.14
Enhancement of Erbium Incorporation with Implantation into Nanoporous GaN.
Chew Beng Soh 1 , Sihui Sim 2 , Sudhiranjan Tripathy 1 , Soo Jin Chua 1 2 , Eduardo Alves 3 Show Abstract
1 , Institute of Materials Research and Engineering, A*STAR (Agency for Science, Technology and Research), Singapore Singapore, 2 , Centre of Optoelectronics, National University of Singapore, Singapore Singapore, 3 , ITN, Sacavém Portugal
9:00 PM - D4.15
First Eu3+@Organo-Si(HIPE) Hybrid Macro-Mesocellular Foams Generation and Associated Photonic Properties.
Nicolas Brun 1 5 , Béatriz Julian-Lopez 2 , Peter Hesemann 3 , Guillaume Laurent 4 , Hervé Deleuze 5 , Clément Sanchez 4 , Marie-France Achard 1 , Annick Babeau 1 , Rénal Backov 1 Show Abstract
1 , Centre de Recherche Paul Pascal UPR 8641 CNRS, PESSAC France, 5 , Institut des Sciences Moléculaires UMR 5255 CNRS Université Bordeaux 1, TALENCE France, 2 , Departamento de Química Inorgánica y Orgánica ESTCE Universitat Jaume I, CASTELLÓN Spain, 3 , Institut Charles Gerhardt UMR 5253 Ecole Nationale Supérieure de Chimie, MONTPELLIER France, 4 , Laboratoire de Chimie de la Matière Condensée de Paris UMR 7574 CNRS Université Pierre et Marie Curie, PARIS France
Designing new porous materials in a monolithic form with framework involving hierarchical pore system and tailored macropore morphologies is an emerging area of technological interest toward heterogeneous catalysis, separation techniques, absorbers, sensors, optics etc. In this direction, the “integrative chemistry” approach , where chemistry and process are strongly coupled, allows the pre-dictated assembling of a large variety of molecular precursors or nanobuilding blocks into engineered hierarchical structures. With this aim, our research group has developed a way to obtain macrocellular silica monoliths, labelled “Si-HIPE”, with a high control on the final macroscopic cells, by using concentrated direct emulsion and lyotropic mesophase . Recently, the elaboration of organosilica based hybrid monoliths exhibiting a hierarchically structured bimodal porous structure in view of final function or polyfunctionalities to be reached, have been processed for the first time [3a,b]. Through co-condensation (“one-pot”) process, where the ORMOSILs (Organically Modified Silanes) are incorporated in the reaction medium and participate to the whole synthesis, or grafting method, which refers to post-synthesis modification of the pre-fabricated materials, many organic functionalities have been anchored to the amorphous silica porous network.With the same strategy, we took benefit of β-diketone and malonamide ORMOSILs derivatives to complex lanthanide europium ions within new Organo-Si(HIPE) matrices . The resulting materials have been thoroughly characterized via a large set of techniques such as SEM, TEM, SAXS, mercury intrusion porosimetry, nitrogen adsorption, FTIR and 29Si CP MAS NMR. Luminescence behavior of this Eu3+@Organo-Si(HIPE) series was also studied and the effects of environment and europium concentration will be discussed.References R. Backov Soft Matter, 2006, 2, 452. F. Carn, A. Colin, M.-F. Achard, H. Deleuze, M. Birot, R. Backov J.Mater.Chem., 2004, 14, 1370. a) S. Ungureanu, M. Birot, G. Laurent, H. Deleuze, O. Babot, B. Julian-Lopez, M.-F. Achard, C. Sanchez, R. Backov Chem.Mater., 2007, 19, 5786 ; b) S. Ungureanu, H. Deleuze, C. Sanchez, M. I. Popa, R. Backov Chem.Mater., Submitted.  N. Brun, B. Julian-Lopez, P. Hesemann, G. Laurent, H. Deleuze, C. Sanchez, M.-F. Achard, R. Backov Chem.Mater., Submitted.
9:00 PM - D4.16
Fullerene Derivatives with a Red Emissive Europium Substituent.
Anita Fuchsbauer 1 , Olesya Troshina 2 , Pavel Troshin 2 , Robert Koeppe 1 , Rimma Lyubovskaya 2 , Serdar Sariciftci 1 Show Abstract
1 Linz Insitute for Organic Solar Cells (LIOS), Johannes Kepler Universtiy Linz, Linz Austria, 2 , Institute of Problems of Chemical Physics of Russian Academy of Science , Chernogolovka, Moscow Region, Russian Federation
Since the discovery of C60 and its derivatives quite some research effort was dedicated to their possible applications in biomedicine . Fullerenes are known to be applicable as photosensitizers and as DNA cleavers  due to singlet oxygen production. In addition, fullerenes can be used as scavengers for free radical species  and as inhibitors for enzymes . The development of biomedical chemistry of fullerenes is limited by their low solubility in water. Quite some research has been done in this field to overcome the solubility problem to get highly water soluble fullerene derivatives useful for biomedical research in vivo and in vitro. For bio-detection in tissues, usually fluorescent tags are attached to bioactive substances. The fullerenes are very strong electron acceptors and luminescence quenchers. Fluorescence of virtually any organic label attached to fullerenes is normally quenched due to a photoinduced electron transfer . We present here a study where the fullerene derivatives were labelled with Eu3+ ions, showing the characteristic emission of the rare earth ion. To our best knowledge this is the first report of luminescent labelled fullerenes.In this study  three different fullerene derivatives (a tetraaminofullerene AmF, a pyrrolidino fullerene PyF and a protonated tetraaminofullerene pAmF) were embedded into rare earth complexes with europium as the central atom. These complexes were synthesized by ligand exchange reactions starting from the pristine fullerene derivatives and a precursor rare earth complex (containing two water and three beta-diketonate molecules as ligands). In the exchange reaction water moclecules were replaced by the pyridyl groups of the fullerene derivative resulting in complexes with the fullerene derivative and remaining beta-diketonate ligands. For biomedical applications we also synthesized a water-soluble Eu3+complex using water-soluble protonated tetraaminofullerene as ligand. This leads to water-solubile fullerene derivatives labelled with lumenescengt Eu3+ tags. Spectroscopic results (absorption, photoluminescence and photoluminescence excitation profiles) show that in organic (or aqueous) solution of the complexes the characteristic emission of the Eu3+ ion at around 614 nm can be clearly seen. The fullerene does not seem to donate energy to the Eu ion but still acts as a quencher for the emission. Even though the emission is quenched by factor of 10-20 it can be still clearly seen and is easy detectable.  S. Bosi, T. Da Ross, G. Spalluto, M. Prato, Eur. J. Med. Chem. 2003, 38, 913-92 A. W. Jensen, S. R. Wilson , D.I. Schuster, Bioorgan. Med. Chem. 1996, 4 (6), 767-779 N. S. Sariciftci, L. Smilowitz, A. J. Heeger, F. Wudl, Science 1992, 258 (5087), 1474-1476 A. Fuchsbauer, O. A. Troshina, P. A. Troshin, R. Koeppe, R.N. Lyubovskaya, N.S. Sariciftci, Adv.Funct.Mat., in press
9:00 PM - D4.17
Monoporphyrinate Lanthanide Complex Functionalized Sol-gel Glass with Strong Near-infrared Emission.
Hongshan He 1 , Andrew Sykes 2 , Xingzhong Yan 1 , David Galipeau 1 Show Abstract
1 Department of Electrical Engineering, South Dakota State University, Brookings, South Dakota, United States, 2 Department of Chemistry, University of South Dakota, Vermillion, South Dakota, United States
The increasing interests in near-infrared emission of ytterbium (ΙΙΙ), neodymium (ΙΙΙ), and erbium (ΙΙΙ) complexes arise from their potential applications in organic liquid lasers, optical-fiber polymers, electroluminescent devices, fluoroimmuno-assays, and down-conversion materials for solar cell; however, the current lanthanide organic materials exhibit poor emission efficiency due to the overlapping of near-infrared emission frequency with X-H (X = O, N, C) vibration frequency from organic matrix. One way to solve this problem is the hybridization of lanthanide complexes with inorganic matrix to suppress this kind of quenching. Recently, we developed a new method for the preparation of stable monoporphyrinate acetate lanthanide methanol solvate, which can be easily bonded to silica frames through coordination of neutral bidentate ligands. Reported here are the synthesis, characterization and photophysical properties of first monporphyrinate lanthanide complex functionalized silica sol gel glass.
9:00 PM - D4.18
Nd Diffusion During Sintering of Transparent YAG.
Joel Hollingsworth 1 2 , Joshua Kuntz 1 , Thomas Soules 1 Show Abstract
1 Photon Science & Applications, Lawrence Livermore National Laboratory, Livermore, California, United States, 2 Materials Science, University of California, San Diego, La Jolla, California, United States
Tuesday, 12/2New Poster D4.18Nd Diffusion During Sintering of Transparent YAG.Joel P. Hollingsworth1, 2, Joshua Kuntz1, Thomas Soules1 INSTITUTIONS (ALL): 1. Photon Science & Applications, Lawrence Livermore National Laboratory, Livermore, California. 2. Materials Science, University of California, San Diego, La Jolla, California. ABSTRACT BODY: Among the many potential benefits of ceramic laser amplifiers is the possibility of controlling the dopant concentration profile before sintering. However, re-distribution of dopant ions during sintering would be an important design consideration in such a process. To study dopant diffusion during sintering, I fabricated layered yttrium aluminum garnet ceramics using undoped powder and similar powder doped with 1 at% Nd. I used vacuum sintering procedures that produce ceramic Nd:YAG laser amplifiers, as well as a variety of other times and temperatures. I then examined Nd concentration profiles and microstructure, with a focus on high-diffusivity paths.
9:00 PM - D4.2
Structural and Optical Properties of Rare Earth Implanted AlN.
Katharina Lorenz 1 2 , E. Alves 1 2 , M. Peres 3 , T. Monteiro 3 , M. N. da Silva 3 , M. Soares 3 , J. Leitao 3 Show Abstract
1 UFA, Instituto Tecnologico e Nuclear, Sacavem Portugal, 2 CFNUL, University of Lisbon, Lisbon Portugal, 3 Departamento de Física e I3N, Universidade de Aveiro, Aveiro Portugal
9:00 PM - D4.3
970 nm Infrared Upconversion in Er3+ and Yb3+ Doped PLZT Glass Thin Films.
Xiaomei Guo 1 , Kewen Li 1 , Yingyin Zou 1 , Hua Jiang 1 Show Abstract
1 , Boston Applied Technologies, Inc., Woburn, Massachusetts, United States
Upconversion effects have been observed in lanthanides doped bulk PLZT (lanthanum modified lead zirconate titanate) transparent ceramics previously., In this work, we report the greatly enhanced upconversion effect observed in unconventional PLZT glass thin films. Erbium and ytterbium ions doped PLZT glass thin films with strong 970 nm infrared upconversion and good optical properties have been fabricated for the first time. The upconversion enhancement is due to the increased Er3+ and Yb3+ doping concentrations, without quenching, enabled by a solution deposition route. The amorphous glass phase, instead of a crystalline ceramic one, possesses better optical properties because of the absence of the grain boundaries that may act as scattering centers and energy traps. In addition, the amorphous glass phase requires less thermal energy (no need for crystallization) and thus a milder processing condition. The upconversion mechanism in this system will be analyzed.. de Camargo et al., “2.8 and 1.55 µm emission from diode-pumped Er3+-doped and Yb3+ co-doped lead lanthanum zirconate titanate transparent ferroelectric ceramic”, APPLIED PHYSICS LETTERS 86, 241112 (2005).. Zheng et al., “Optical properties of Er3+/Yb3+-codoped transparent PLZT ceramic”, Physica B 403, 44–49 (2008).
9:00 PM - D4.4
Electroluminescence, Charge Trapping and Clustering in Rare-Earth Implanted SiO2-Si Light-Emitting Diodes.
Alexei Nazarov 1 2 , I. Tyagulskii 1 2 , S. Tyagulsiy 1 2 , L. Rebohle 2 , S. Prucnal 2 , J. Lehmann 2 , J. Biskupek 3 , U. Kaiser 3 , W. Skorupa 3 Show Abstract
1 National Academy of Sciences of Ukraine, Institute of Semiconductor Physics,, Kyiv Ukraine, 2 Institut fur Ionenstrahlphysik und Materialforschung, Forschungszentrum Dresden-, Dresden Germany, 3 , University Ulm, , Ulm Germany
In this work a comparative study of charge trapping, electroluminescence intensity (ELI) and clustering in SiO2 implanted by different rare-earth (RE) impurities (Eu, Tb, Gd, Er, Tm) with following high-temperature annealing is performed to clarify the connection between the electrical properties, the structure of the luminescent centers, the ELI and the EL spectra. RE impurities were implanted into the bulk of thermally grown SiO2 on n-type Si. The implanted doses were chosen in such a way that the maximum concentration corresponded to 0.1, 0.5, 1.5 and 3.0 at %. To activate the RE implanted impurities a post implantation furnace anneal in the temperature range of 800-1100 °C for 30 min and flash lamp annealing (FLA) for 20 ms at 1000 °C in a nitrogen ambient have been carried out. The ITO layer was used as a transparent electrode. Charge trapping was studied by the shifting of the high-frequency CV characteristics and the changing of the applied voltage during constant current electron injection from Si into SiO2. The EL signal was recorded at the same injection regime at room temperature in the wavelength range of 300 to 750 nm. Some control structures were studies by transmission electron microscopy with high resolution (XTEM).It was shown that RE impurities such as Tb, Gd, Er and Tm implanted into SiO2 cause mainly net positive charge trapping in the range of the injected charge from 1E15 to 2E17 e/cm2 and stable ELI of their main luminescence lines in green, UV, IR and blue spectral region of the EL spectra, respectively. Above 1E18 e/cm2 of the injected charge an electron trapping in the bulk of the oxide and a hole trapping at the SiO2-Si interface is observed for all types of the RE impurities. The electron trapping correlates with the EL quenching of the main EL lines for all studied RE implanted structures with the exception of the Eu implanted one. The Eu implanted oxide demonstrates effective electron trapping up to 1E20 e/cm2 without EL quenching of the main studied EL lines: in red spectral region with a maximum at 618 nm (5D0-7F2 transition for Eu3+ ions); in the blue-green spectral region around 460-470 nm and in blue-violet one at 410 nm (corresponding to a 4f6d-4f7 transition of the Eu2+ ion). The XTEM measurements discovered that the clustering in the Eu-implanted SiO2 is enhanced considerably in comparison with the Tb-implanted one. It is suggested that the enhanced electron trapping in the Eu implanted structures is associated with enhanced clustering, which is partly caused by low valency (2+) oxides existing for the Eu impurity such as EuO and Eu3O4. The use of FLA for the Eu implanted SiO2 results in a decrease of the nanocluster size and an increase of the ELI in the red region of the spectrum.
9:00 PM - D4.5
Red Emission Properties of Eu3+ doped GaN Powders Prepared by a Na Flux Method.
Ei Brown 1 , Uwe Hommerich 1 , Takahiro Yamada 2 , Hisanori Yamane 2 , John Zavada 3 Show Abstract
1 Physics, Hampton University, Hampton, Virginia, United States, 2 Institute of Multidisciplinary Research fo Advanced Materials, Tohoku University, Sendai Japan, 3 Electrical and Computer Engineering, North Carolina state University, Raleigh, North Carolina, United States
The emission properties of rare earth (RE) doped GaN continue to be of interest for applications in full color displays, solid-state lighting, and optical communications. Visible (red, green, blue) and IR electroluminescent devices have been fabricated using different RE doped GaN epitaxial thin-films. More recently, red laser emission from Eu doped GaN was also demonstrated. In the past few years, RE doped GaN powders were prepared using different methods including freeze-dried precursors, flux techniques and combustion synthesis. In this work, we present results of photoluminescence (PL) studies of Eu3+ doped GaN powder prepared by a Na flux method. Under above-gap excitation, GaN:Eu powders showed bright red luminescence at ~ 621 nm, which corresponds to the intra-4f Eu3+ transition of 5D0 --> 7F2 state. The integrated PL intensity of the red emission was quenched only by a factor of two under above-gap pumping for the temperature range 10-300 K. The Eu3+ emission line originating from 5D0 --> 7F0 transition was comprised of two peaks located at ~585.8 nm and ~588.2 nm, which suggests the presence of more than one Eu3+ center in the GaN powder. The average Eu3+ lifetime was determined to be ~250 µs at room-temperature. More details of the PL properties of Eu3+ doped GaN powder including temperature and excitation-wavelength dependent PL studies, as well as site-selective PL excitation studies will be presented at the conference.
9:00 PM - D4.6
ESR Study of Er-concentration Effect in Photoluminescent Semiconductor GaAs:Er,O.
Masashi Fujisawa 1 , Atsushi Asakura 2 , Elmasry Fatma 2 , Susumu Okubo 3 , Hitoshi Ohta 1 2 3 , Yasufumi Fujiwara 4 Show Abstract
1 Department of Frontier Research and Technology, Kobe University, Kobe Japan, 2 Graduate School of Sciences, Kobe University, Kobe Japan, 3 Molecular Photoscience Research Center, Kobe University, Kobe Japan, 4 Graduate School of Engineering, Osaka University, Osaka Japan
Photoluminescence (PL) originated from Rare-earth ions incorporated in semiconductors has attracted a considerable attention. In particular, Er3+ doped III-V semiconductor exhibits temperature-stable PL at around 1.5 μm. The wave length of 1.5 μm lies in the minimum loss region of silica fibers. GaAs co-doped with Er and O (GaAs: Er,O) has also sharp simple PL spectra of Er3+ . The luminescent Er center has been identified as Er3+ at the Ga site with two adjacent oxygen atoms (Er-2O center). However a large number of Er atoms in GaAs do not participate in the host-excited PL. This is one of unsolved problems in the luminescence mechanism of GaAs: Er,O. Therefore, it is crucially important to classify the luminescent Er center from the other Er centers. Recently Fujiwara et al. have reported that the PL intensity still remains even in the very low concentration of Er (less than 1017 cm-3). This result seems to be a clue to distinct the luminescent Er center from the other Er centers in GaAs: Er,O. Electron spin resonance (ESR) measurement is a powerful method to obtain the information of local environment at magnetic ions in a solid. In this study we performed X-band ESR measurement in order to investigate the Er-concentration effect in GaAs: Er,O. The GaAs: Er,O samples were grown on (001) SI-GaAs substrates by the organometallic vapor phase epitaxy (OMVPE) method . The Er concentrations of GA05529, GA05522, and GA030278 [as estimated by secondary ion mass spectroscopy (SIMS) measurement] were 9.2x1018, 8.3x1017, and less than 1.0x1017 cm-3, respectively. ESR measurements have been performed from T = 4.7 K to 18 K using the Bruker ESR spectrometer EMX081 with a TE103 rectangular cavity and the Oxford He flow cryostat ESR 900 at Kobe University. The frequency of the microwave was 9.49 GHz and the external magnetic field was swept up to 9000 G. Three types of Er-related ESR signals were observed in GA05529, GA05522, and GA030278. The resonance fields of these signals are consistent with those reported previously . From the Er concentration dependence of linewidth, the lineshape analysis, and the temperature dependence of integrated intensity, we conclude that Er-center are not homogeneously-distributed in GaAs and the distance between Er3+ ions is not large. Furthermore, Er3+ ions can be antiferromagnetically coupled via the super-exchange interaction. The details will be discussed at the symposium.This work is supported by a Grant-in-Aid for Creative Scientific Research (No. 19GS1209) and a Grant-in-Aid for Scientific Research on Priority Areas (No. 17072005) from the Ministry of Education, Culture, Sports, Science and Technology. The authors are also grateful for the financial support from the Department of Frontier Research and Technology, Kobe University. K. Takahei, and A. Taguchi, J. Appl. Phys. 74, 1979 (1993). Y. Fujiwara, et al., Physica B 273-274, 770 (1999). M. Yoshida, et al., J. Appl. Phys. 96, 4189 (2004).
9:00 PM - D4.7
Optical Properties of High Mole-Fraction Europium Doped Beta Gallium Oxide.
Patrick Wellenius 1 , Robert Kolbas 1 , John Muth 1 , Steven LeBoeuf 2 , Michael Aumer 2 , Jesse Tucker 2 Show Abstract
1 Electrical and Computer Engineering, North Carolina State University, Raleigh, North Carolina, United States, 2 , Valencell, Inc., Raleigh, North Carolina, United States
Rare-earth doped phosphors have found a number of applications including displays, optical networks and lasers due to their rich luminescence spectra and potentially long radiative lifetimes. Beta phase gallium oxide is a wide bandgap (4.7 eV) semiconductor and represents a novel host that can be efficiently doped by rare earth elements. In this study, very smooth thin films of gallium oxide doped with europium above 10 mole percent have been deposited by Pulsed Laser Deposition on sapphire substrates at 850°C. Photoluminescence and cathodoluminescence spectra demonstrate characteristic europium peaks, the most intense appearing at 611 nm due to the 5D0 to 7F2 transition. Photoluminescence effects related to dopant concentration were studied using a deep UV optical pump. Films were further optically characterized by transmission and refractive index measurements. Structural effects of europium doping were characterized by atomic force microscopy and x-ray diffraction. Additionally, the wide bandgap of gallium oxide enables investigation of UV absorption bands present in europium that could not be studied in narrower bandgap hosts.
9:00 PM - D4.8
Enhanced 1.54 μm Luminescence in Er-doped ZnO Nanoparticle Films via Indirect Excitation.
Zhengda Pan 1 , S. Morgan 1 , A. Ueda 1 , R. Aga 1 , H. Xu 2 , S. Hark 2 , R. Mu 1 Show Abstract
1 , Fisk University, Nashville, Tennessee, United States, 2 , The Chinese University of Hong Kong, Hong Kong China
Photoluminescence (PL) of Er-doped ZnO nanoparticle films was studied. The films were grown on silicon (100) and fused silica substrates using e-beam evaporation. The evaporating targets used were sintered pellets of ZnO and Er2O3 mixtures with different Er concentrations. The films were subsequently annealed at 700 °C in air for an hour. The SEM images revealed nano-sized ZnO grain structure. PL was measured at two excitation wavelengths, 325 and 514.5 nm. The 325 nm is used for exciting the host semiconductor ZnO and 514.5 nm is used for directly exciting Er3+ ions in the ZnO host. Er3+ luminescence was observed from the annealed films using either indirect (325 nm) or direct (514.5 nm) excitations. It has been found that the indirect excitation is significantly more efficient than the direct excitation in producing 1.54 μm photoluminescence. Our results show that the indirect excitation is about 40 times more efficient than the direct excitation in producing 1.54 μm photoluminescence. With indirect excitation, the Er3+ luminescence observed is attributed to energy transfer from ZnO host to the Er3+ ions doped. Energy transfer from e-h pairs resulting from ZnO host excitation may provide efficient routes for exciting Er3+ ions inside nano-crystalline particles of the films. This research is supported by US National Science Foundation NSF-CREST- CA: HRD-0420516, NSF-STC CLiPS - grant no. 0423914, and US Department of Defense (DOD)/ARO contracts: W911NF-05-1-0453, and W911NF-04-1-0400.
9:00 PM - D4.9
Characterization of Er3+ Ions in Aluminum Nitride Crystals Using Electron Paramagnetic Resonance.
Shan Yang 1 , S. Evans 1 , N. Giles 1 , L. Halliburton 1 , G. Slack 2 , S. Schujman 2 , K. Morgan 2 , R. Bondokov 2 , S. Mueller 2 Show Abstract
1 Physics, West Virginia University, Morgantown, West Virginia, United States, 2 , Crystal IS, Inc., Green Island, New York, United States
Electron paramagnetic resonance (EPR) provides information about rare-earth ions in a variety of host lattices, both insulators and semiconductors. This technique monitors the ground state of the rare-earth impurity and provides information about the symmetry of the occupied site. Thus, data from EPR often complement the results obtained from separate optical absorption and luminescence experiments. The g values obtained from EPR experiments usually deviate significantly from 2.0 and serve as sensitive probes of the local crystal electric field. Hyperfine splittings are large and are often well resolved. These hyperfine patterns are unique to each rare-earth element, reflecting specific nuclear spins and isotope abundances, and provide unambiguous identifications in those cases where trace amounts of rare-earth impurities are unintentionally present in a crystal.Rare-earth ions are important dopants in aluminum nitride (AlN) and gallium nitride (GaN) because they offer the potential to combine efficient below-band-gap optical emission at room temperature with superior electronic and mechanical properties. An EPR spectrum from Er3+ ions has been observed in a bulk single crystal of AlN grown at Crystal IS by the seeded sublimation-recondensation method. These Er3+ ions were introduced into the crystal during growth, and had a concentration of approximately 2 x 1016 cm−3. The Er3+ EPR signal, monitored at 4.5 K, exhibited axial symmetry (the unique axis is parallel to the  direction in this wurtzite lattice) and showed well-resolved hyperfine splittings due to 167Er nuclei. Principal values for the g and hyperfine matrices are g‖ = 4.337, g| = 7.647, A‖ = 454 MHz, and A| = 796 MHz. The nuclear electric quadrupole parameter is estimated to be P = 7 MHz. We conclude that the observed Er3+ ions occupy aluminum sites in the AlN crystal and have no nearby defects. The results of the present study are compared to an earlier EPR study of Er3+ in GaN by Palczewska et al. . Work done at WVU was supported by NSF Grant No. 0804352.. M. Palczewska et al., Solid State Communications 114, 39 (2000).
Volkmar Dierolf Lehigh University
Yasufumi Fujiwara Osaka University
Uwe Hommerich Hampton University
Pierre Ruterana CIMAP
John Zavada North Carolina State University
D5: Rare Earth Doping and Devices in Silicon-related Materials
Wednesday AM, December 03, 2008
Room 201 (Hynes)
9:30 AM - D5.1
β-Ga2O3 Nanostructures Doped with Rare Earth Ions for Photonic Nanodevices.
Emilio Nogales 1 , Bianchi Mendez 1 , Javier Piqueras 1 , Jose Angel García 2 Show Abstract
1 Departamento de Física de Materiales, Universidad Complutense de Madrid, Madrid Spain, 2 Departamento de Física Aplicada II, Universidad del País Vasco, Bilbao Spain
9:45 AM - D5.2
Size Control, Surface Control and Surface Modification of Doped Lanthanide Phosphate Nanocrystals.
Katharina Hickmann 1 , Karsten Koempe 1 , Anke Oertel 1 , Markus Haase 1 Show Abstract
1 Inorganic Chemistry I- Materials Research, University of Osnabrück, Institute of Chemistry, Osnabrück, Niedersachsen, Germany
10:00 AM - **D5.3
Deposition of Single-phase ErxY2-xSiO2 Thin Films for a Compact, High Gain High Optical in Compact Volume on a Si Chip.
Jung Shin 1 , Kiseok Suh 1 , Jee Soo Chang 1 Show Abstract
1 Physics, KAIST, Daejeon Korea (the Republic of)
11:00 AM - **D5.4
Fabrication and Evaluation of Self-organized Er2SiO5 Crystalline Films for the 1.5μm Emitters and Amplifiers in Silicon Photonics.
Tadamasa Kimura 1 , Hideo Isshiki 1 Show Abstract
1 Electronic Engineering, Univ. Electro-Communications, Tokyo Japan
ErSiO crystalline compounds such as erbium silicates (Er2Si2O7, Er2SiO5) and Er2O3 have been attracting much attention as new light source materials for silicon photonics. These silicates, however, had not been studied in detail as optical materials for silicon photonics until self-organized Er2SiO5 crystalline films with a highly-ordered layered structure were found by H.Isshiki et al. The self-organized Er2SiO5 has unique characteristics totally different from Er-doped Si-based materials. Er2SiO5 contains Er as one of the constituent elements at 25 at.%, and shows a layered structure with a period of 0.86nm. Due to the crystalline and ordered structure, Er3+ ions are subjected to a uniform crystal field, which results in single optically active Er3+ centers and the emission of sharp luminescence peaks with a Stark splitting even at room temperature. The high Er contents of Er2SiO5 make possible to fabricate a small light emitter and an light amplifier at 1.54 μm for use in silicon photonics. However, the important issues of Er2SiO5 silicates accompanying the high Er content are the concentration quenching and up-conversion. The energy migration from excited to non-excited Er ions may be increased due to high Er contents. However, the highly ordered Er2SiO5 may contain few defects which lead to the nonradiative transitions. The up-conversion in Er2SiO5 silicates relative to the radiative transition is also estimated to be much smaller than expected from data for Er-doped silicon-based materials, since the decay rate of Er3+ from 4I13/2 to 4I15/2 is shorter than 100μs in Er2SiO5 silicates, in contrast to several milliseconds for Er-doped silicon-based materials. In fact, the luminescent intensity of ordered Er2SiO5 is strong enough and decays with a single decay constant by three orders of magnitudes, and these results are indications of relatively small nonradiative transitions in spite of high Er contents in ordered Er2SiO5. The contribution of up-conversion was studied using a ridge-type waveguide and green and other emissions of Er3+ due to up-conversion was observed only at very high input power of 1.48 μm excitation light.In this presentation are shown various methods (sol-gel, MOMBE, laser ablation) for the fabrication of self-organized Er2SiO5 crystalline films on Si substrates, their crystalline structure, and the self-organization process. The photoluminescence spectra and the decay characteristics are shown in relation to the fabrication process and crystalline structure. Though the bulk Er2SiO5 emits light only by direct excitation of Er3+, it is shown that Er2SiO5 crystalline films embedded in a SiOx matrix, which are formed by phase separation from Si-rich non-stoichiometric starting materials using the sol-gel method, can be excited indirectly via e-h recombination. Finally, up-conversion characteristics and a possibility of Er2SiO5 silicates for laser diodes and optical amplifiers are discussed.
11:45 AM - D5.6
Huge Performance Increase of Tb-implanted MOS Light Emitting Devices with SiOxNy Layers Moderating Hot Carrier Effects.
Lars Rebohle 1 , Jiaming Sun 2 1 , Slawomir Prucnal 3 1 , Alexei Nazarov 4 1 , Igor Tyagulskii 4 1 , Manfred Helm 1 , Wolfgang Skorupa 1 Show Abstract
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf e.V., Dresden Germany, 2 Key Laboratory of Weak Light Nonlinear Photonics, Nankai University, Nankai China, 3 Department of Ion Beam Physics and Ion Implantation, Marie Curie-Sklodowska University, Lublin Poland, 4 Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, Kiev Ukraine
The electrical stability of Tb-implanted SiO2 light emitting devices was drastically improved by using a SiON dielectric buffer layer. For fabrication thermally grown oxide layers on Si were implanted with Tb followed by a thermal treatment and the deposition of a SiON protection layer by plasma-enhanced chemical vapor deposition. The structures were finally provided with an indium tin oxide front contact and an aluminum rear contact. The incorporation of the SiON layer increases the breakdown electric field from 7.5 to 10.5 MV/cm and enhances the operation time of the light emitters up to three orders of magnitude under constant injection currents. By varying the SiO2 and SiON layer thickness it was found that the largest stability enhancements can be achieved if the SiON layer thickness is more than twice the thickness of the SiO2 layer.The beneficial role of the SiON layer is mainly explained by reducing the chance of destructive avalanche breakdowns in the oxide layer and by an efficient cooling process of hot electrons moving in the conduction band of SiO2. The latter effect is based on the lower electric fields in SiON as compared to SiO2 and the lower band offset of SiON relative to the gate electrode. In addition, the SiON layer acts as a diffusion barrier against moisture from the working ambient and broadens the operation range of the light emitters on the voltage scale.
12:00 PM - D5.7
Optimization of Si Nanoparticle Size in Nanostructured Er-Si:Al2O3 Thin Films to Enhance the Er3+ Luminescence by Photon and Electron Excitation.
Rosalia Serna 1 , Sara Nunez-Sanchez 1 , Emilio Nogales 2 , Bianchi Mendez 2 Show Abstract
1 Instituto de Optica, CSIC, Madrid, Madrid, Spain, 2 Departamento de Fisica de Materiales, Facultad de Ciencias Fisicas, Universidad Computense, Madrid, Madrid, Spain
12:15 PM - D5.8
Photoluminescence Properties of Erbium-doped Silicon Oxycarbide Thin Films with a Low Carbon Content (SiC0.20O1.70).
Vasileios Nikas 1 , Spyros Gallis 1 2 , Himani Suhag 1 , Mengbing Huang 1 , Alain Kaloyeros 1 Show Abstract
1 College of nanoscale schiences and engineering, State university of New York at Albany, Albany, New York, United States, 2 , IBM Microelectronics, Semiconductor Reasearh and development, East Fishkill, New York, United States
12:30 PM - D5.9
Influence of Upconversion on Er2SiO5 Waveguide Light Emitting Devices.
Hideo Isshiki 1 , Takayuki Nakajima 1 , Tadamasa Kimura 1 Show Abstract
1 Electronic Engineering, The Univ. of Electro-Communications, Tokyo Japan
ErSiO crystalline compounds such as erbium silicates (Er2Si2O7 and Er2SiO5) and Er2O3 have been attracting attention as a new light source material for small size emitting devices on silicon. Since the Er silicates contain a lot of Er ions above 20 at% as the constituent element, the crystalline nature prevents the concentration quenching and shows 1.53μm PL spectrum fine structure even at room temperature. However it has been pointed out that the upconversion limits emission efficiency and optical gain for 1.53μm light in the Er silicate waveguides. In this paper, we discuss influence of the upconversion on Er2SiO5 waveguide light emitting devices. So far we have reported the upconversion emission from Er2SiO5 waveguide, which corresponds to the transition from 4S3/2 or 2H11/2 to 4I15/2, and shown the upconversion is less effective in comparison with Er2O3 aggregations because of the extreme fast decay time of Er2SiO5. In the case using 1480nm excitation light, the upconversion process is considered to be via two excited states(4I13/2, 4I9/2). Then excited state absorption is not effective in comparison with the cooperative upconversion, because the cross section is small. We considered rate equations of the cooperative upconversion. Populations of the excited states are labeled N1 (4I15/2), N2 (4I13/2), N4 (4I9/2) and N7 (4S3/2 and 2H11/2). In the case of cooperative upconversion form the first excited state, terms of C24N22 and C47N2N4 are added in the rate equation to account for loss of population N2 through upconversion, with C24, C47being the cooperative upconversion coefficient. The upconversion coefficient C24 has been estimated to be 3.5x10-16 cm3s-1 for an Er2O3/Al2O3 strong Er-Er interaction system. Assuming C24=C47, we attempted to calculate the optical gain and amplified spontaneous emission (AES) in Er2SiO5 waveguide.Extreme fast decay time of Er2SiO5 less than 100μs has been reported. Basically, the fast decay causes raising the gain threshold of excitation photon flux and increase of AES. Then the radiative transition and the upconversion is even, and if stimulated emission occurs, the radiative transition overcomes the upconversion process in Er2SiO5. However slow decay time above 100μs is overcome the upconversion process and the gain threshold is also raised up. It seems that the upconversion coefficient is little bit over estimated. In order to apply to waveguide amplifiers, it is necessary to exactly determine the upconversion coefficient, and the realistic device design(gain, length, etc.). Considering dipole-dipole transition as a base process of the upconversion, the upconversion factor can depend on the exciton density (or population of excited state), because distance between each exciton depends on the population and is less than the critical distance (about 2nm) in Er2SiO5 under the highly excitation condition. We have also attempt to analyze with this consideration.
12:45 PM - D5.10
Erbium-based Active Materials Integrated with Wafer-bonded Silicon Slot Waveguides for Laser and Optical Amplifier Applications.
Ryan Briggs 1 , Gerald Miller 1 , Harry Atwater 1 Show Abstract
1 Thomas J. Watson Laboratory of Applied Phyiscs, California Institute of Technology, Pasadena, California, United States
On-chip light sources compatible with current silicon-based manufacturing techniques are an essential component for the next generation of optoelectronic devices. To this end, we present a design for an integrated silicon-based optical amplifier for operation near 1540 nm that combines silicon waveguide technology with erbium-doped gain materials. Our device is based on a horizontal silicon-glass-silicon “slot” waveguide structure that takes advantage of high index contrast to tightly confine light within a thin layer of erbium-doped glass. Slot waveguides have been demonstrated in vertical configurations , but strategies for depositing optically active materials in the slot remain difficult to implement. By fabricating horizontally oriented layers, active slot materials can be deposited using standard thin film techniques. In addition, lateral confinement can be achieved with lithographically patterned waveguides, similar to current silicon-on-insulator (SOI) devices [2,3]. Our design can also serve as a platform for electrical excitation, in analogy to previously demonstrated tunnel-injection devices .
We fabricate horizontal slot structures by wafer bonding pairs of commercially available SOI wafers with silica-based slot layers at the bonding interface. With this technique, the silicon layers both above and below the slot are single-crystalline and thus exhibit low optical loss near 1540 nm. The process is compatible with passive silica slot layers as well as layers composed of optically active erbium-doped glass. The silicon layers are approximately 140 nm thick and the slot layers range from 10 to 25 nm. Layer dimensions and material quality are verified using spectroscopic ellipsometry and cross-sectional TEM. By analytical calculation, we show that structures with this geometry support a single mode for transverse-magnetic (TM) polarized light. Furthermore, we show that for an active slot layer thickness of only 25 nm, the modal gain for the TM mode can theoretically reach 50 % of the bulk gain of the slot material.
For use as active slot layers, erbium-doped silica and soda lime glass films are deposited by dc ion-beam sputtering prior to bonding. Erbium concentrations range from 0.7 to 1.3 atomic %, as measured by Rutherford backscattering spectroscopy (RBS). The films exhibit strong photoluminescence response near 1540 nm under resonant excitation at 488 nm. Waveguide signal enhancement at 1540 nm under optical pumping will be discussed. We will also present strategies for implementing the erbium-doped slot waveguide design as an optically and, ultimately, electrically pumped on-chip infrared light source.
 Q. Xu, et al., Optics Lett. 29, 1626-1628 (2004).
 K. K. Lee, et al., Optics Lett. 26, 1888-1890 (2001).
 M. A. Webster, et al., Appl. Phys. Lett. 87, 231108 (2005).
 R. J. Walters, G. I. Bourianoff, H. A. Atwater, Nature Mat. 4, 143-146 (2005).
D6/MM9: Joint Session: Er Doped Si Nanostructures
Wednesday PM, December 03, 2008
Room 309 (Hynes)
2:30 PM - **D6.1/MM9.1
Rare Earth Ion Beam Processing for Silicon Photonics.
Wolfgang Skorupa 1 , Lars Rebohle 1 , Slawomir Prucnal 1 , Charaf Cherkouk 1 , Manfred Helm 1 Show Abstract
1 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Dresden Germany
Combining silicon-based electronic circuits with optoelectronic functionality is one of the key challenges for the future semiconductor technology. Such work must not only be devoted to the “telecommunication” wavelength of 1.54 µm because there are much more applications requiring light sources from the UV to IR wavelength range. In our work we employed ion beam processing to embed different rare earth (RE) luminescent centers (Gd, Ce, Tm, Tb, Eu, Er) into the silicon dioxide layer of purpose-designed Metal-Oxide-Silicon-based Light Emitting Devices (MOSLEDs) with advanced electrical performance. Efficient electroluminescence was obtained from UV to infrared with a transparent top electrode made of indium-tin oxide. Several developments for improving the device stability will be proposed related to charge compensation and the elimination of defects in SiO2. The electrical and electroluminescence properties of these devices are discussed and evaluated in respect of possible applications for biosensing applications. As an example our recent effort to detect estrogens in drinking water will be discussed.
3:00 PM - D6.2/MM9.2
The Role of Hydrogen in the Luminescence-center-mediated Er3+ Excitation in Si-rich SiO2 with and without Si Nanocrystals.
Pieter Kik 1 , Oleksandr Savchyn 1 , Ravi Todi 2 , Kevin Coffey 2 Show Abstract
1 CREOL, The College of Optics and Photonics, University of Central Florida, Orlando, Florida, United States, 2 AMPAC, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, Florida, United States
Recently we have shown that erbium excitation in Si-doped SiO2 films occurs predominantly through isolated silicon related luminescence centers (LC) in the oxide. This conclusion seemed to contradict studies in which hydrogen passivation of Si nanocrystals leads to a significant improvement of the Er3+ photoluminescence (PL) intensity. In order to study the role of hydrogen passivation in the luminescence-center-mediated excitation of Er3+, Er-doped Si-rich SiO2 films with significantly different microstructures were prepared. These samples were subsequently passivated in forming gas (5% H2, 95% N2) at different temperatures. Photoluminescence measurements on samples containing no detectable silicon nanocrystals (annealed at 600°C) revealed little change in the indirectly excited Er3+ PL intensity. In contrast, photoluminescence measurements on samples containing silicon nanocrystals (annealed at 1100°C) revealed a strong (factor ~10) increase in the Er3+ PL intensity as the passivation temperature is increased from room temperature to 500°C. This increase is accompanied by a similar increase in the Si nanocrystal emission intensity, suggesting that nanocrystal mediated excitation does play an important role in the Er3+ excitation mechanism. These observations are attributed to two interrelated effects, namely, (a) an increase in the density of fully passivated optically active nanocrystals due to the removal of silicon dangling bonds upon passivation, and (b) a concurrent reduction in nonradiative Er3+ relaxation from levels above the 4I13/2 level due to a direct interaction of excited Er3+ ions with silicon dangling bonds. It is argued that such an interaction is reasonable based on the known energies of the Er3+ excited states and the location of the Si dangling bond state in the silicon bandgap. These findings suggest that silicon sensitized Er3+ gain media must either be processed at low temperature to avoid the formation of a crystalline Si phase in the SiO2 host, or at high temperature followed by hydrogen passivation.
3:15 PM - D6.3/MM9.3
Er-doped Si Nanolayers for Generation of IR and THz Range Radiation.
Salvatore Minissale 1 , Tom Gregorkiewicz 1 Show Abstract
1 Van der Waals Zeeman Institute, University of Amsterdam, Amsterdam Netherlands
Er-doped silicon structures have undergone extensive investigations for development of optical materials and devices. In that research, important drawbacks have been pointed out, which need to be overcome in order to achieve intense, and eventually also stimulated, room temperature emission. Mostly, low optical activity and multiplicity of optically active centers formed by an Er3+ in Si are identified as the major obstacles. More recently, Si/Si:Er multinanolayer structures have emerged as a novel material with superior optical properties, which could allow for realization of optical gain. Such a hope comes from the fact that the Er-related 1.5 μm emission from Si/Si:Er multinanolayers features a spectrum comprising only a few lines with a very narrow and homogeneous linewidth of ΔE < 8 μeV. This can be traced back to the presence of only a single type of Er-related optical center (labeled Er-1). Moreover, optical activity of Er dopants in these structures is higher than in thick Si:Er layers commonly used.In this presentation, we will review the unique properties of Si/Si:Er multinanolayers: the single center formation and its microscopic structure, the level of optical activity, and relation between optical and electrical properties. We will show that combining photoluminescence and magneto-optical spectroscopy it is possible to draw a detailed level scheme for the 4I15/2 ground state of the Er3+ ion involved in the Er-1 center. Transitions within the ground state, between individual sublevels split due to the Stark effect induced by the local crystal field on Er3+ ion, fall into the THz range, with the relevant wavelengths being expected at 43, 91, 144, and 169 μm. In full analogy to the 1.5 μm emission in the IR domain, a very small linewidth can be expected also for these THz transitions. In the second part of the presentation we will report on our recent investigations concerning the THz range transitions. The study has been conducted by the time-resolved pump-probe absorption technique, since the initial linear absorption measurements proved inconclusive. This was due to B dopants present in the substrate, whose relatively strong internal transitions between shallow acceptor states appear in the same range, and therefore preclude observation of the weaker (“forbidden” transition) Er-related signals.We will present results obtained by pump-probe experiments, conducted in the standard and also in the “transient grating” configuration, which conclusively identify an optical transition at 43 μm and determine the related time constant as τ≈50 ps. We argue that this value reflects a nonradiative multiphonon recombination within the 4I15/2 ground state of an Er3+ ion. To the best of our knowledge, this is the first observation of an optical transition within a multiplet of a rare earth ion. Finally, we will address the practical potential of Si/Si:Er nanolayers for development of a compact and electrically-driven all-Si THz source.
4:00 PM - **D6.4/MM9.4
Towards an Er Doped Silica Amplifier Sensitized by Silicon Nanoclusters.
Nicola Daldosso 1 , Daniel Navarro-Urrios 1 , Alessandro Pitanti 1 , Romain Guider 1 , Lorenzo Pavesi 1 , Larysa Khomenkova 2 , Fabrice Gourbilleau 2 , Richard Rizk 2 Show Abstract
1 Physics, University of Trento, Povo - Trento Italy, 2 , CIMAP, UMR CEA/CNRS 6176, Caen France
The use of erbium doped amplifiers for widespread integration presents some difficulties: Er ions pair interactions, small excitation cross-section, high power laser diodes as pump source,excited state absorption, …. The use of sensitizers for erbium ions can relax the stringent conditions for the pump source. A good sensitizer should present a high absorption cross section and has to transfer efficiently energy to Er. The capacity of silicon nanoclusters (Si-nc) to act as sensitizers has opened the route towards an all-optical (and even electrical) Si-based amplifiers operating in the third telecommunication window. In fact, Si-nc (either amorphous or crystalline) have broad absorption spectrum and very large absorption cross sections with respect to Er in stechiometric silica. Moreover, a clear breakthrough would be the possibility of having an electrical excitation of rare-earth ions through the Si–nc. Unfortunaltly, the main obstacles to achieve net optical amplification in Si-nc based Er doped waveguides are currently Carrier Absorption (CA) losses and the low number of Er ions coupled to Si-nc (few %). The reason for this low number is still under discussion. We present here our last results on the optical properties of reactive magnetron co-sputtered waveguides containing Si-nc and Er in a SiO2 matrix. The material has been optimised in terms of the increasing of PL intensity and lifetime (up to 5 ms) as well as the decreasing down to few dB/cm of the propagation losses in rib-loaded waveguides. We have reduced CA induced losses to less than 0.2dB/cm (at pump fluxes as high as 10(20)ph/cm2 s) both through an engineering of Si-nc size (i.e. by tuning the Si content and the annealing conditions) and coupling high percent of Er ions to Si-nc. Around 25% (the highest fraction up to date) of the optically active erbium population has been inverted through indirect excitation (pumping with a 476nm laser line), leading to internal gain coefficients of abouot 1dB/cm.By time resolved measurements we demonstrate that the energy transfer mainly occurs from Si-nc to the metastable level of Er ion and that the transfer time is extremely fast (tens of ns). Furthermore, we show that there are no traces of Auger back-transfer or Excited State Absorption mechanisms and that pair induced quenching is not an issue in our samples, being the limited interaction distance between Si-nc and Er ions the main reason.We believe that these results re-validate the feasibility of an optical amplifier based on this material since the sensitization of Er by Si-nc is not limited by fundamental physical processes. The major, if not the only, constraining factor in achieving full Er inversion is the limited interaction distance between Si-nc and Er ions, that can be solved by a careful material optimization. We acknowledge financial support by EC through the LANCER project (FP6-IST-2005-033574).
4:30 PM - **D6.5/MM9.5
Optimum Coupling between Er Ions and Si Nanoclusters Sensitizers for High Performance Integrated Photonics.
Richard Rizk 1 , Julien Cardin 1 , Khalil Hijazi 1 , Larysa Khomenkova 1 , Fabrice Gourbilleau 1 Show Abstract
1 CIMAP, CNRS, Caen France
The sensitizing role played by the broad-band high-absorbing Si nanoclusters (Si-nc) towards Er ions in silica is still the object of tremendous research activities. Such a coupling induces some 103-104 enhancement of the effective excitation of Er ions, and allows also the use of high power LEDs or electrical excitation instead of the expensive pump lasers. However, the energy transfer from Si-nc to Er ions is mainly governed by their separating distance which should be lower than a value as low as ~0.5 nm, hence limiting the fraction of coupled Er to 0.5-3%, as reported so far. The present contribution deals with the effort made to maximize this fraction of couple Er, through a careful engineering of the composition of the active material, together with the analyses of various features: sensitizers’ nature, energy transfer process(es), optical losses/gain. The Er-doped silicon-rich SiO2 layers were grown by magnetron co-sputtering of confocal targets, under a reactive (H2+Ar) or Ar plasma, before being submitted to thermal treatments. While the reactive approach deposition has allowed the increase of the fraction of coupled Er to about 11% of the total Er content, the film grown at 500-600°C by the co-sputtering of three confocal cathodes under pure Ar, has led the a further enhancement of this fraction and the majority of the optically active Er ions are now coupled to Si-nc. This paves the way to the achievement of a net optical gain and then light amplification. Such an unprecedented result would be due to the growth of very small and highly dense Si-based sensitizer entities, of few tens of atoms, acting as point-like defects inducing deep isolated electronic states instead of the electronic band structure of Si-nc containing thousand(s) of atoms. These ‘atomic’ scaled sensitizers are much more numerous than the usual Si-nc and their formation would be due to some specific growth kinetics at relatively high substrate temperature and subsequent thermal treatment, leading to three inherent advantages: very high density favoring a maximum coupling with the neighboring Er ions, very small or negligible confined carrier absorption inducing losses, and very fast energy transfer (tens of ns) induced by some trap-mediated excitation of Er that appears reminiscent of that in crystalline Si. Finally, such an optimum distribution of the Si excess has showed good transport of carriers injected by electrical excitation, as demonstrated by the observation of a high electroluminescence. We acknowledge financial support by EC through the LANCER project (FP6-IST-2005-033574).
5:00 PM - D6.6/MM9.6
Sensitized Erbium Emission in Silicon Nanocrystals-based Superlattice Structures.
Rui Li 1 2 , Joe Warga 1 2 , Selcuk Yerci 1 2 , Luca Dal Negro 1 2 Show Abstract
1 Department of Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States, 2 Photonics Center, Boston University, Boston, Massachusetts, United States
At present, there is a strong need to engineer Si-compatible nanostructures for efficient light emission under optical and electrical excitation. The widely investigated material system, Si-nanocrystals (Si-nc) in SiO2 glass matrices, shows very efficient (60%) room- temperature light emission under optical pumping. However, the presence of an insulating SiO2 matrix significantly hinders the fabrication of stable and efficient electrically driven light sources. Therefore, it is important to explore novel CMOS-compatible solutions based on the excitation of Si-ncs dispersed in alternative, electrically injectable materials structures. We report on time-resolved Si-ncs emission, Er sensitization and electroluminescence in a novel Si-based, CMOS compatible quantum system based on Si/Si-rich nitride (SRN) nanocrystals arranged in a superlattice structure. The structure was fabricated by RF magnetron sputtering deposition followed by thermal annealing from 500°C to 1000°C. High-resolution TEM pictures show 2nm diameter Si clusters dispersed in SRN layers with controlled thickness between 4nm and 50nm. Erbium incorporation and activation is achieved by direct co-sputtering of the Si-rich layers. We will first discuss Si-N bond surface state related emission mechanism of SRN by low temperature photoluminescence measurements. Then we will discuss the important role of annealing temperature for SRN emission and Er activation in Si-nc-based superlattice structures (Si-nc-SLs) and show that energy transfer occurs on the nanosecond time scale. In addition, we will report on the ultra-fast time-resolved emission dynamics of superlattices, and estimate the maximum transfer rate and transfer efficiency in these novel systems. Our results from low temperature emission dynamics (4K) directly address the nature of energy transfer and as a phonon mediated non-radiative process. We believe that light emission from Si-ncs-based SLs can provide alternative routes towards the engineering of Si-based light sources for 1.54µm applications.
5:15 PM - D6.7/MM9.7
Significant Improvement of Photoluminescence Intensity and Lifetime from Er3+ Ions Coupled to Si Clusters in Si-rich-SiO2 Layers.
Larysa Khomenkova, 1 , Fabrice Gourbilleau 1 , Christian Dufour 1 , Julien Cardin 1 , Richard Rizk 1 Show Abstract
1 CIMAP, ENSICAEN, Caen Cedex 04 France
The role of silicon clusters whether crystallized or amorphous as efficient sensitizers of Er3+ ions is well established. Most of the works reported so far have stressed on the very small proportion of Er3+ ions benefiting from the ‘effective’ and efficient excitation through silicon clusters. This prevents the development of compact and CMOS-compatible photonic devices. The present work aims at exploring the ways to improve the coupling between silicon clusters and optically active Er3+ ions. The reactive magnetron sputtering from two confocal SiO2 and Er2O3 cathodes in argon-hydrogen plasma was used to deposit Er3+-doped Si-rich-SiO2 layers with controlled composition. The structural, compositional and photoluminescence properties of the layers were examined. The effect of the deposition parameters as well as subsequent annealing procedure was investigated in order to reach an optimum Er3+-related photoluminescence intensity and an improved lifetime. Careful analyses were made through the dependence of these parameters on the pumped photon flux and the excitation wavelength.It was found that the adopted approach allows significant enhancement of both PL intensity and lifetime. For example, the comparison with the best samples obtained up to now shows i) the increase of Er3+ emission lifetime from 5 ms to about 10 ms and ii) the increase of the PL intensity, at resonant (488nm) or non-resonant (476nm) excitations, by a factor of three. The overall results were analyzed in terms of coupling rate between the Er3+ ions and Si-nc, together with the impact of up-conversion processes. The project “LANCER” (IST-2005-033574) is acknowledged.
5:30 PM - D6.8/MM9.8
Investigation of the Er3+ Location in Si-rich Silicon Oxide by 3D Atom Probe Tomography.
Etienne Talbot 1 , Rodrigue Larde 1 , Fabrice Gourbilleau 2 , Richard Rizk 2 , Philippe Pareige 1 Show Abstract
1 , GPM - Université de Rouen - UMR CNRS 6634, Saint Etienne du Rouvray France, 2 , CIMAP, UMR CNRS 6252, ENSICAEN, Caen France
5:45 PM - D6.9/MM9.9
Enhanced Erbium Near Infrared Emission in Doped Group IV Oxide Nanowires Using a GeOx Sensitizer.
Jeffery Coffer 1 , Ji Wu 1 Show Abstract
1 Chemistry, Texas Christian University, Fort Worth, Texas, United States
Group IV oxide nanowires provide efficient platforms for the confined modulation of light. As an active emitter in the near IR, however, such materials are limited by direct excitation of optically-active centers such as erbium (III) ions incorporated into the matrix with a corresponding low absorption cross section. To overcome these limitations, one logical approach is to add a sensitizer such as Si nanocrystals or Ag+ ions that have much larger absorption cross sections than Er+3 and can be employed to excite the rare earth ions more efficiently via a carrier-mediated process. We have developed facile routes to erbium-doped Group IV oxide nanowires and nanofibers using a combination of sol gel condensation chemistry and electrospinning. In the work described here, we focus on nanofibers of SnO2 as a host matrix, a highly optical transparent n-type semiconductor with a wide band gap of 3.6 eV at 300 K. Such nanofibers doped with erbium can ideally serve as building blocks to assemble more optoelectronic units on a single chip via a bottom-up approach. Since Er+3 ions can only be directly excited in as-prepared Er-doped SnO2 nanofibers, an effective sensitizer is required. Previous work published by our group has identified GeOx as an efficient sensitizer for erbium ions; therefore, it is logical to introduce this sub-oxide into Er-doped SnO2 nanofibers for the deliberate purpose of producing a carrier-mediated excitation enhancement pathway into a conductive host. In this study, we employ a vapor transport method and a corresponding in situ oxidation-reduction reaction to introduce various amounts of GeOx into the Er-doped SnO2 nanofibers. The composition and structure of these nanofibers were characterized using a combination of TEM, SEM, X-ray energy dispersive spectroscopy (EDX), and micro-Raman spectroscopy. It is demonstrated that the photoluminescence intensity of Er-doped SnO2 nanofibers at 1540 nm can be enhanced via a carrier-mediated mechanism by almost two orders of magnitude after the introduction of this germanium suboxide.
D7: Poster Session
Thursday AM, December 04, 2008
Exhibition Hall D (Hynes)
9:00 PM - D7.1
Luminescence Lifetime Thermometry in YSZ.
Matthew Chambers 1 , Vince Kispersky 1 , David Clarke 1 Show Abstract
1 Materials Department, University of California, Santa Barbara, Santa Barbara, California, United States
The radiative lifetime of rare-earth dopants in YSZ can be used to measure temperature in a fast, non-contact fashion, a necessity for thermometry in environments such as jet turbine engines. Depending on the dopant used, temperature sensitivity can be achieved from room temperature up to over 1100°C. In addition to temperature, the decay profiles of luminescence intensity (versus time after excitation) reveal information about the site multiplicity of dopants in YSZ as it progresses from as-deposited single phase metastable, tetragonal-prime phase (t’) to a two phase mixture of tetragonal and cubic phases. The use of Eu3+ as a probe of local structure is described and the types and relative amounts of its site populations are presented through a range of zirconias ranging from essentially unstabilized zirconia to delta-phase Y4Zr3O12. The origins of diverse decay profiles from materials of the same nominal composition are elucidated.One of the remarkable findings is that, for Eu:YSZ, the relation of radiative lifetime to temperature (or, the lifetime-temperature map) is insensitive to stabilizer segregation in aged 7YSZ, oxygen content, and is also only slightly sensitive to Eu3+ concentration. The reasons for this stability include the preferential coordination of intrinsic vacancies, the relatively small number of extrinsic vacancies, and the dominance of Eu3+ emissions of certain populations over others.
9:00 PM - D7.11
Electroluminescence from Erbium-Doped Amorphous Silicon Oxycarbide Thin Films.
Himani Suhag 1 , Vasilis Nikas 1 , Spyros Gallis 1 2 , Mengbing Huang 1 , Alain Kaloyeros 1 Show Abstract
1 College of Nanoscale Science and Engineering, The University at Albany-SUNY, Albany, New York, United States, 2 Semiconductor Research and Development Center, IBM Microelectronics, Hopewell Jct, New York, United States
9:00 PM - D7.13
Rare-earth Doped Polymeric Gain Media for Visible Amplification.
Paula Russell-Hill 1 , Takeyuki Kobayashi 1 , Werner Blau 1 Show Abstract
1 School of Physics, Trinity College Dublin, Dublin Ireland
Rare earth-doped glasses, such as erbium and neodymium, are widely used as gain media for laser sources with narrow pulse width or as optical amplifiers with high gain, high power conversion and broad spectral width. The aim of this work to is to provide spectroscopic information to develop rare earth doped polymer waveguide amplifiers for use in optical communications systems, as they are inexpensive to manufacture and more easily reproduced than their inorganic counterparts. The problems involving the poor solubility of rare earth ions in inorganic hosts are well established. In an effort to overcome these issues and to achieve higher gain per unit length, the rare earth ions are encapsulated by organic ligands and are doped into a polymer host matrix, namely polymethyl methacrylate and polystyrene. The optical waveguides fabricated from these polymers show low-loss communication windows in the visible region. The main rare earth complexes being investigated are those of europium and terbium, which have strong emission peaks at approximately 610 nm and 545 nm, respectively.In this work we present a spectroscopic study of the rare earth complexes in solution and in a solid state polymer host; the absorption and stimulated emission cross-section are measured for a range of polymer and solvent hosts. By changing the combination of host polymer and solvent, the aim is to achieve higher active dopant concentrations. The solutions containing specified amounts of the rare earth complex and host polymer were spin coated onto a Pyrex substrate. The variable stripe length method was employed to characterize optical gain in these planar waveguides. Upon pulsed nanosecond photoexcitation by the third harmonic of a Nd:YAG laser, the gain coefficient of up to 3 cm-1 at 614 nm has been determined for an europium-doped planar waveguide.
9:00 PM - D7.14
Increase in Excitation Efficiency of Er3+-Related 1.53μm Emission from Er2SiO5 Crystallite Embedded in SRSO.
Masaki Oe 1 , Yu Fujiwara 1 , Hideo Isshiki 1 , Tadamasa Kimura 1 Show Abstract
1 , Univ.Electro Communication, Tokyo Japan
9:00 PM - D7.15
Effects of Preparation Method and Doping Concentration on the Luminescent Properties of (Sb3+, Eu3+) Co-doped YBO3 Prepared using a Hydrothermal Method and a Solid-state Process.
Fushan Wen 1 , Jinhyeok Kim 2 Show Abstract
1 College of Chemistry & Chemical Engineering, China University of Petroleum, Dongying, Shandong, China, 2 Photonic and Electronic Thin Film Laboratory, Department of Materials Science and Engineering , Chonnam National University, Kwangju Korea (the Republic of)
9:00 PM - D7.16
Comparison of n-type Gd2O3 and Gd-doped HfO2 Electronic Structure.
Yaraslov Losovyj 1 2 , David Wooten 3 , Juan Colon-Santana 1 , N. Lozova 2 , James Petrosky 3 , A. Sokolov 1 , Jinke Tang 4 , Wendong Wang 4 , I. Ketsman 1 , Peter Dowben 1 Show Abstract
1 Physics and Astronomy, University of Nebraska (Linicoln), Lincoln, Nebraska, United States, 2 Center for Advanced Microstructures and Devices, Louisiana State University, Baton Rouge, Louisiana, United States, 3 Physics and Nuclear Engineering, Air Force Institure of Technology, Wright Patterson Air Force Base, Ohio, United States, 4 Physics and Astronomy, University of Wyoming, Laramie, Wyoming, United States
We find that the position of the 4f Gd states and the extent of their hybridization in oxides is an issue pertinent to understanding compound 4f and 5f semiconductors. In the Gd3+ and mixed valence systems, Gd 4f hybridization with nearest neighbor atoms is expected [1,2] and observed. Gd2O3 and Gd-doped HfO2 films were deposited on p-type silicon substrates in a reducing atmosphere to create a n-type material. The Gd 4f photo excitation peak at roughly 7 eV and 5 eV below the valence band maximum was identified using resonant photoemission for both Gd2O3 and Gd-doped HfO2 films, respectively. In the case of Gd2O3, strong hybridization with the O 2p band was demonstrated; and crystal field effects were identified consistent with monoclinic structure of Gd2O3 on Si (100). The rectifying (diode like) properties of Gd-doped HfO2 to silicon and Gd2O3 to silicon heterojunctions are demonstrated.
9:00 PM - D7.17
Photoluminescent Properties of Eu2+-activated M3MgSi2O8 (M=Ba,Sr,Ca).
Yoshinori Yonesaki 1 , Takahiro Takei 1 , Nobuhiro Kumada 1 , Nobukazu Kinomura 1 Show Abstract
1 Interdisciplinary Graduate School of Medical and Engineering, University of Yamanashi, Kofu Japan
Presently utilized phosphors are generally activated by doping of transition-metal or rare-earth metal ions. Eu2+-doped BaMgAl10O17 (BAM) is widely adopted as a blue phosphor satisfying the demands for brightness and chromaticity. However, BAM has a serious issue of the deterioration in emission intensity during panel assembly processes at high temperature and a long-time use. Therefore, it has been urgent need to develop a new host material applicable for blue phosphors. In this work, photoluminescence properties of Eu2+-doped M3MgSi2O8 prepared by a standard solid-state reaction in a reduced condition were investigated in terms of the crystal structure. Rietveld refinements of X-ray powder diffraction data have confirmed that M3MgSi2O8 crystalline phase consists of a sequential stacking of layer framework built up by corner-sharing MgO6 octahedra and SiO4 tetrahedra and alkali earth metal ions. Meanwhile, M3MgSi2O8 phase could be divided into trigonal-type or monoclinic-type, depending on the crystal structure. Eu2+-doped M3MgSi2O8 exhibited an intense emission assigned to 5d-4f electron transitions of Eu2+ ions under 254 nm excitation. The emission color was sensitive to the structure-type rather than the ratio of alkali earth metal ions.
9:00 PM - D7.18
Sensitized Luminescence from Rare Earth-Doped Nanocrystalline Titania Microspheres.
Jianfang Wang 1 Show Abstract
1 Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR China
Rare earth luminescence emissions arising from their 4f intra-shell transitions are sharper, more photostable, and longer-lived than those from organic fluorophores and inorganic semiconductor nanocrystals. Such attractive spectroscopic properties make rare earth ions potentially useful for a variety of photoluminescence-based lighting, lasing, signaling, and imaging techniques. However, since the f-f transitions are parity-forbidden, direct excitation of rare earth ions is inefficient, and simultaneous excitation of multiple rare earth ions is difficult. To fully realize their potential optical and biotechnological applications, the capability to excite multiple rare earth ions efficiently and simultaneously over a broad spectral range is strongly desired. I will report on rare earth-doped nanocrystalline titania microspheres that exhibit bright narrow bandwidth emission from rare earth ions when excited above the semiconductor bandgap of anatase titania nanocrystals. Rare earth-doped nanocrystalline titania microspheres are prepared using an inexpensive and scalable ultrasonic aerosol spray method in conjunction with the evaporation-induced self-assembly process. Uniformly distributed anatase titania nanocrystals with controlled sizes are produced inside these microspheres by thermal treatment at varying temperatures. They function as sensitizers to absorb light and transfer energy to rare earth ions, leading to intense and narrow bandwidth emissions. This energy transfer mechanism allows for the simultaneous excitation of multiple rare earth ions that are doped in the nanocrystalline titania microspheres over a broad spectral range at a high efficiency.Related publication: L. Li, C.-K. Tsung, Z. Yang, G. D. Stucky, L. D. Sun, J. F. Wang, C. H. Yan, Adv. Mater. 2008, 20, 903.
9:00 PM - D7.19
Fabrication and Optical Property of Rare-earth Oxide-doped Synthetic Opals.
Tadashi Nakamura 1 , Yuri Yamada 1 , Hisashi Yamada 1 , Kazuhisa Yano 1 Show Abstract
1 , Toyota Central R&D Labs., Inc., Aichi Japan
We have succeeded in synthesizing highly monodispersed mesoporous silica spheres (abbreviated as MMSS hereafter) with diameters in the submicrometer range . We have already demonstrated the fabrication of various types of functional synthetic opals, using MMSS and their derivative composites as building blocks. [2-4]. The incorporation of rare-earth oxide nanocrystals (Y2O3:Tb or Y2O3:Eu) into mesopores of MMSS and the subsequent self-assembly of the composite spheres would result in the formation of fluorescent synthetic opals. Due to their photonic band structure derived from a periodic modulation of the dielectric constant, the resultant fluorescent opals have the potential to tailor the spontaneous emission of rare-earth oxide embedded. Herein, we report the fabrication and optical properties of fluorescent synthetic opals consisting of MMSS-derived rare-earth oxide-doped spheres.Rare-earth oxide/silica nanocomposite spheres were synthesized via a template ion exchange process and the subsequent heat treatment at 1273 K. In the template ion exchange process, the surfactant ions of as-synthesized MMSS were exchanged for the rare-earth ions in a methanolic solution. XRD and TEM-EDS analyses confirmed that Y2O3:Tb or Y2O3:Eu nanocrystals were successfully embedded inside the silica spheres. The resultant Y2O3:Tb/SiO2 composite spheres exhibited green emission with narrow bands corresponding to the intra-4f transitions. Likewise, the Y2O3:Eu/SiO2 composite spheres exhibited red emission. These fluorescent composite spheres were readily self-assembled into a three-dimensionally ordered array by using a fluidic cell [2-4]. Each array had a face-centered cubic opal structure with its (111) plane oriented parallel to the substrate, and exhibited a well-defined  stop band. The particle size of composite spheres were adjusted so that the  stop band of the opal structure overlapped the emission band of the rare-earth oxide embedded. It was found that the emission from the fluorescent opal was strongly modulated by the presence of a stop band and that the intensity of emission exhibited a distinct minimum along the direction parallel to the  stop band.References:  K. Yano et al., J. Mater. Chem., 14, 2004, 1579.  Y. Yamada et al., Langmuir, 22, 2006, 2444.  T. Nakamura et al., J. Mater. Chem., 16, 2006, 2417.  T. Nakamura et al., J. Mater. Chem., 17, 2007, 3726.
9:00 PM - D7.2
Effects of Ultraviolet Light Irradiation on Photoluminescence of Ce Doped Silicate Glasses.
Arika Nakada 1 , Tetsuo Kishi 1 , Atsuo Yasumori 1 Show Abstract
1 Department of Materials Science and Technology, Tokyo University of Science, Chiba Japan
It has been known that photoluminescence (PL) of rare-earth ions doped glasses are useful for various photonic applications such as laser devices and optical recoding media. Ce doped oxide glasses are one of the good candidates for new photo-functional materials such as three-dimensional optical memory, because of their ultraviolet (UV) photosensitivity. For example, it was reported that the Ce3+ ions in the phosphate glass were photo-ionized to Ce4+ after exposure to UV light irradiation, and the released electrons were captured by the other co-doped ions like Eu3+ . In this case, Ce3+ ions showed PL in wide-ranging colors depending on their surrounding host, while Ce4+ ions do not show PL because of 4f electrons’ absence. On the other hand, among major oxide glasses, silicate glass is superior in chemical durability and thermal stability, and consequently is suitable for practical use. Furthermore, it is worth investigating the PL property of Ce single-doped glasses in order to know the effect of the host glass composition. In this study, we investigated the optical absorption and PL properties of Ce doped silicate glasses, and the effects of UV irradiation and subsequent heat treatment on PL intensities of the glasses. The appropriate compositions of Na2O-CaO-B2O3-Al2O3-SiO2 system were selected as a host silicate glass. The Ce doped glasses in this composition were prepared by a conventional melt-quenching method. The UV light irradiation to the glasses was carried out by use of Hg-Xe lamp for 15min. The irradiated sample was subsequently heat-treated at 500oC for 60min. This UV irradiation and heat treatment cycle was repeated several times. Their absorption and PL spectra excited at 336nm were measured. The as-quenched samples showed the absorption due to Ce3+ and Ce4+ in the range of 200-300nm, and the PL peak around 400 nm due to Ce3+. In UV-irradiated samples, the absorption of Ce3+ decreased and that of Ce4+ increased, hence their PL intensity decreased almost by half. By the heat treatment of the UV-irradiated glass, the absorption and PL properties recovered, and the whole shape and peak of the spectra were almost same as those of the as-quenched sample. Up to 5 times, both absorbance and PL intensity recovered without any degradation. We consider that these changes of the absorption and the PL intensity are owing to the valence change of Ce ions; the UV light irradiation makes Ce3+ ions release their electrons, which may be trapped by glass network and/or its defects. Then, the heat treatment enables Ce4+ ions to recombine with the electrons again. These results indicate that Ce doped silicate glasses have a great potential to be utilized as the rewritable three-dimensional optical memory media, since their PL intensity can be easily controlled by the UV irradiation and the heat treatment. E. Pavel and L. Tugulea, J. Solid State Chem., 134, 362 (1997).
9:00 PM - D7.20
Strongly Enhanced Erbium Near-Infrared Emission in Dye-Loaded Nanoporous Materials.
Agnieszka Mech 1 , Angelo Monguzzi 1 , Francesco Meinardi 1 , Riccardo Tubino 1 , Jakub Mezyk 1 Show Abstract
1 Dipartimento di Scienza dei Materiali, Università degli Studi di Milano- Bicocca, Milano, Lombardia, Italy
There is a growing demand for low cost near infrared (NIR) light sources for application in telecommunication devices. Among the lanthanide series there are several rare-earth ions, e,g, Er3+, Nd3+, and Yb3+, which exhibit emission in the NIR region and may be used in materials for optical amplifiers in the super-high speed communication.Although these ions exhibit very favorable luminescent properties, their absorption cross-sections are very small, leading to inefficient emission from the 4f levels under direct excitation. This limitation can be removed by using NIR luminescent lanthanide complexes with organic ligands in which the emission of the lanthanide ion is sensitized by the intramolecular energy transfer from the organic component. On the other hand, however, it is well known that the coupling between metal ions electronic states and vibrational overtones of O-H and C-H bonds of organic ligands is able to quench very efficiently the NIR emission. It was already shown that application of the halogenated organic components increases significantly the quantum yield of the NIR emission of the complex . Unfortunately, the presence of halogenated groups in organic part strongly hampers the formation of complexes with lanthanide ions and even if such compound can be obtained it is more fragile and instable compared to its non-halogenated counterpart. In this regard the lanthanides incorporated into a zeolite matrix provide a promising alternative [2, 3]. In such systems emission from the metal ion can be efficiently sensitized by the organic molecule loaded into a zeolite channel, bypassing the requirement of the creation of real chemical bond between them. This gives an opportunity to use as the sensitizers the organic molecules, for which the synthesis of the stable complex would fail. The NIR emission lifetimes reported up to date are, however, of the order of 1 μs and the fabrication of an efficient organic NIR emitter is still a challenging task.In this communication we present the intense sensitized NIR emission of Er3+ ions exchanged within a zeolite matrix, excited via energy transfer from decafluorobenzophenone, molecules, which fill the zeolite channels, and act as light harvesting antennae. The resulting NIR emission is strongly enhanced, and its lifetime is more then two orders of magnitude longer then in non fluorinated erbium organometallic complexes. The promising optical properties of this material as well as the fact that the functionalized zeolite can be successfully incorporated into a polymer, may open the way to manufacture the efficient NIR light sources useful in the communication applicationsP. Glover, A. Bassett, P. Nockemann, B. Kariuki, R. Van Deun and Z. Pikramenou, Chem. Eur. J., 2007, 13, 6308 – 6320A. Manguzzi, G. Macchi, F. Meinardi, R. Tubino, M. Burger, G. Calzaferri, Appl. Phys. Lett., 2008, 92, 123301-1-3Y. Wada, M. Sato and Y. Tsukahara, Angew. Chem. Int. Ed. 2006, 45, 1925 –1928
9:00 PM - D7.4
Nd-Doped Gallium Oxide Thin Films Grown by Radiofrequency Magnetron Sputtering.
Céline Lecerf 1 , Philippe Marie 1 , Xavier Portier 1 , Fabrice Gourbilleau 1 Show Abstract
1 CIMAP, ENSICAEN, Caen France
9:00 PM - D7.5
Infrared Emission Properties of Ho Doped KPb2Cl5.
Olusola Oyebola 1 , Uwe Hommerich 1 , Sudhir Trivedi 2 , Althea Bluiett 3 , J. Zavada 4 Show Abstract
1 , Hampton University, Hampton, Virginia, United States, 2 , Brimrose Corporation, Baltimore, Maryland, United States, 3 , Elizabeth City State University, Elizabeth City, North Carolina, United States, 4 , North Carolina State University, Raleigh, North Carolina, United States
The development of near- and mid-infrared (IR) laser sources continues to be of current interest for applications such as optical communications, remote sensing, medical treatment, and IR countermeasure techniques. Potassium lead chloride (KPb2Cl5) has recently emerged as a novel IR laser host with a low maximum phonon energy. The narrow phonon spectrum of KPb2Cl5 extends to only ~200 cm-1, which leads to small non-radiative decay rates and efficient IR emission. In contrast to many other halides, KPb2Cl5 is non-hygroscopic making it an attractive host material for solid-state laser applications. In this work, we present the infrared emission properties of Ho3+ doped KPb2Cl5 and evaluate its potential as a novel IR gain medium. Following optical excitation at 885 nm, several IR emission bands were observed with peak wavelengths at 1065 nm, 1191 nm, 1134 nm, 1664 nm, 2020 nm, 2862 nm, and 3948 nm. Further spectroscopic studies were focused on the mid-IR emission at ~3.9 μm arising from the Ho3+ transition 5I5 -> 5I6. The emission lifetime of the 5I5 level was measured to be 4.9 ms at room-temperature and remained nearly constant when cooling the sample to 15 K. The nearly temperature independent lifetime suggests a small non-radiative decay rate for the 5I5 excited state of Ho3+ as predicted by the energy-gap law for KPb2Cl5. More details on the materials preparation, crystal growth, and IR optical properties of Ho doped KPb2Cl5 will be presented at the conference.
9:00 PM - D7.6
Correlation between Ferroelectric and Fluorescent Properties by introducing Eu Atoms into Strontium Bismuth Tantalate Films.
Koji Aizawa 1 , Yusuke Ohtani 1 Show Abstract
1 OEDS R&D Center, Kanazawa Institute of Technology, Ishikawa Japan
Rare-earth-ion (Ln3+)-doped strontium bismuth tantalate (SBT) films have also attracted much attention as a promising candidate for optoelectronic applications because of the luminescence of Ln3+ as well as for memory application due to excellent fatigue property. We investigated the crystallinity, electrical and fluorescent properties of Eu-doped SBT (Eu-SBT) films deposited by spin-coating. Particularly, effects of Eu-doping on ferroelectricity and photoluminescence (PL) of these films were studied. Sr-deficient Eu-SBT films were formed on Pt (200 nm)/Ti (50 nm)/SiO2/Si substrates by using (1-x)SrBi2Ta2O9 and xSr0.8(Bi2, Eu0.2)Ta2O9 (x=0-1) mixed precursor solutions with a concentration of 0.33 mol/kg, in which Bi content was fixed. On the other hand, Bi-excess Eu-SBT films were formed by using (1-x)Sr0.8Bi2.2Ta2O9 and xSr0.8(Bi2, Eu0.2)Ta2O9 solutions, in which Sr content was fixed at 0.8. The precursor solutions were spin-coated at 2000 rpm for 30 s and the coated films were dried at 140oC for 5 min in air due to the evaporation of the solvent. To remove the organic elements, the dried films were calcined at 350oC for 5 min in air. The thickness of these films was approximately 50 nm after calcination and this procedure was repeated until the required thickness was obtained. Finally, the deposited films were annealed at a temperature of 850oC for 30 min in air at an atmospheric pressure due to crystal growth.From X-ray diffraction analysis, the diffraction peaks from Aurivillius phases were observed in the Eu-SBT films as well as in the SBT films. In addition, these diffraction peak positions were shifted to larger angle direction than that of a pure SBT film. In Sr-deficient Eu-SBT films, the lattice parameters along a- and c-axes at the mixing ratio x=1 in comparison with x=0 decreased approximately 0.36 and 0.19 %, respectively. The remnant polarization (Pr) values of the Sr-deficient Eu-SBT films with mixing ratio x of 0 and 1 were approximately 6.6 and 5.8 μC/cm2, respectively. From PL measurement at a wavelength of 615 nm as a function of mixing ratio, the PL intensity increased without changing the remnant polarization until mixing ratio x=1. On the other hand, the PL intensity of the Bi-excess Eu-SBT films was also proportional to the mixing ratio, whereas, the Pr values were decreased by Eu-doping. In conclusion, the PL intensity of the Sr-deficient Eu-SBT films was increased by Eu doping without almost changing the remnant polarization.The authors thank K. Murata and H. Watanabe for their technical assistant. This work was partly supported by a High-Tech Research Center Project Grant from the Ministry of Education, Culture, Sports, Science and Technology, a Grant-in-aid for Scientific Research (No. 18560316) from the Japan Society for the Promotion of Science, and a Grant (Research for Promoting Technological Seeds, No. 06-014) from the Japan Science and Technology Agency.
9:00 PM - D7.7
Energy Transfer from the Er3+ to Ge Nanocrystals During Electroluminescence in MOSLEDs.
Aloke Kanjilal 1 , Lars Rebohle 1 , Matthias Voelskow 1 , Wolfgang Skorupa 1 , Manfred Helm 1 Show Abstract
1 Semiconductor Materials Division (FWIM), Forschungzentrum Dresden-Rossendorf (FZD), Dresden Germany
It is well established that Si nanocrystals (NCs) can act as sensitizers in Er-doped SiO2 during optical pumping [1-3]. In fact, following the recombination of excitons (electron-hole pairs) in optically excited Si NCs the energy is transferred to the higher energy levels of the nearby Er3+ ions, which subsequently decay to the ground state by intra-4f transitions. Among those, the 4I13/2 → 4I15/2 radiative transition has attracted substantial interest since the respective luminescence at ~ 1.53 μm corresponds to the maximum transparency window of silica-based optical fibers . Ge is another group-IV element with similar electronic properties to that of Si. We have examined the impact of Ge NCs in Er-doped SiO2 layers by investigating electroluminescence (EL) of the metal-oxide semiconductor (MOS) structures, where the Er-doped Ge-rich SiO2 layers have been prepared by ion implantation technique combined with rapid thermal annealing (RTA). The samples have been prepared by two steps: (i) 130 keV Ge ions have been implanted with a dose of 2 × 1016 ions/cm2 in a 200 nm thick thermally grown SiO2 layers