11:30 AM - I12.7
Localisation of Excitation in InGaN Epilayers and Quantum wells.
Kevin O'Donnell 1
1 Physics, University of Strathclyde, Glasgow United Kingdom
Show AbstractThe scalability of the excitation-emission spectra of InGaN epilayers and quantum wells provided early evidence for a common origin of the remarkable optical properties of these commercially important materials. Phase segregation on the nanoscale (accidental QD formation) has generally been accepted as the mechanism underlying this scalability (O’Donnell et al, PRL 82, 237 (1999)). Recently, however, the downsizing of the InN bandgap, from 2 to about 1 eV, has prompted a re-examination of the observations. Here, we present new structural evidence obtained from comparative Ga and In K-edge EXAFS studies across practically the whole composition range of InxGa1-xN epilayer samples. The mean In-Ga and Ga-In next-nearest-neighbour (NNN) separations are found to be unequal for In-poor samples. The degree of inequality, increasing with decreasing InN fraction x, correlates with luminescence efficiency in the range 0.1
11:45 AM - I12.8
Optical Properties of Gallium Nitride Microdisks Fabricated by Photoelectrochemical Etching.
Adele Tamboli 1 , Rajat Sharma 1 , Elaine Haberer 1 , Kwan Lee 2 , Shuji Nakamura 1 , Evelyn Hu 1
1 Materials, University of California, Santa Barbara, Santa Barbara, California, United States, 2 Physics, University of Oxford, Oxford United Kingdom
Show AbstractThe microdisk laser is a promising device geometry for studying material properties of gallium nitride and achieving low-threshold blue lasers. Because microdisks have a simple design and do not require mirror fabrication, they avoid many loss mechanisms common to other nitride lasers. Microdisk lasers have been studied in many material systems recently and have shown high quality optical modes and low lasing thresholds. Microdisks support whispering gallery modes (WGMs) in a circular resonant cavity where light is confined by total internal reflection. The modes propagate along the periphery of the disk, and light is emitted radially. Optical isolation is usually achieved by a dry etch step to form a pillar followed by a selective wet etch to undercut the active region. In GaN, this undercut step is difficult because of the lack of a wet etchant.In this work, we use bandgap selective photoelectrochemical (PEC) etching to undercut a GaN microdisk with InGaN active region[1]. Photoelectrochemical etching consists of an above-bandgap light source and an electrochemical cell. Light incident on the sample creates electron-hole pairs in layers with a bandgap smaller than the incident photon energy. Holes are driven to the surface, where they react with an electrolyte, allowing etching to occur. We use a Xe lamp to generate electron-hole pairs in an InGaN sacrificial layer, which is then etched in HCl. In this way, we are able to form an undercut, mushroom-shaped structure of high optical quality.Previous GaN microdisks fabricated in this manner have shown high quality modes and lasing[1]. We will focus on recent improvement to the fabrication process, leading to drastically reduced thresholds and more repeatable results. GaN microdisks in the size range of 1-8 μm were fabricated using electron beam or optical lithography, reactive ion dry etching, and PEC undercut etching. These disks were studied using room temperature microphotoluminescence measurements with a 325 nm He-Cd CW pump laser. Optical modes were observed with quality factors as high as several thousand. These modes were identified as WGMs and radial modes by FDTD simulations. Lasing characteristics of these devices were explored under CW conditions.Acknowledgments Funding provided by the Department of Defense/NDSEG fellowship and DMEA under the Center for Nanoscience Innovation for Defense.Reference[1] E. D. Haberer, R. Sharma, C. Meier, A. R. Stonas, S. Nakamura, S. P. DenBaars and E. L. Hu, Appl. Phys. Lett. 85 (2004) 5179.
12:00 PM - I12.9
Enhancement of Light Extraction in GaN using Photonic Crystals.
Kelly McGroddy 1 , Aurelien David 2 1 , Cedrik Meier 3 , Rajat Sharma 1 , Steven DenBaars 1 , Claude Weisbuch 2 1 , Evelyn Hu 1
1 Materials, University of California, Santa Barbara, Santa Barbara, California, United States, 2 , Laboratoire Charles Fabry de l'Institut d'Optique, Orsay France, 3 Experimental Physics, University of Duisburg-Essen, Duuisburg Germany
Show Abstract12:15 PM - I12.10
III-nitride Air-gap Microstructures for Optoelectronic Applications.
Rajat Sharma 1 , Yong-Seok Choi 2 , Chiou-fu Wang 3 , Shuji Nakamura 1 , Evelyn Hu 1 2
1 Materials Department, UCSB, Santa Barbara, California, United States, 2 California NanoSystems Institute (CNSI), University of California Santa Barbara (UCSB), Santa Barbara, California, United States, 3 Physics Department, UCSB, Santa Barbara, California, United States
Show Abstract12:30 PM - I12.11
Phonon Decay in GaN and AlN and Self-heating in Devices Based on These Materials.
Mark Holtz 1 , D. Song 1 , S. Nikishin 1
1 , Texas Tech University, Lubbock, Texas, United States
Show Abstract12:45 PM - I12.12
First-principles Study on the Direct/indirect Transiton of III-V Nitride Semiconductor Alloys.
Chang-Youn Moon 1 , Jingbo Li 1 , Su-Huai Wei 1 , Adele Lim 2 , Yuan Feng 2
1 , National Renewable Energy Laboratory, Golden, Colorado, United States, 2 Department of Physics, National University of Singapore, Kent Ridge Singapore
Show AbstractI13: Optical Devices
Session Chairs
Thursday PM, November 30, 2006
Room 311 (Hynes)
2:30 PM - I13.1
1.3 - 2.3 Micron Intersubband Transitions i GaN/Aln Superlattices.
Eric DeCuir 1 , Jinqiao Xie 2 , Emil Fred 1 , Avinash Muddasani 1 , Brandon Passmore 1 , Morgan Ware 3 , Omar Manasreh 1 , Hadis Morkoc 2 , Greg Salamo 3
1 Electrical Engineering, University of Arkansas, Fayetteville, Arkansas, United States, 2 Engineering School, VCU, Richmond, Virginia, United States, 3 Physics, University of Arkansas, Fayetteville, Arkansas, United States
Show AbstractIntersubband transitions in the1.3-2.5 micron spectral range were observed in Si-doped molecular beam epitaxy grown GaN/AlN superlattices using near infrared spectroscopy technique. The peak position of the intersubband transition is blue shifted as the GaN well width is decreased. Two intersubband transitions were observed in samples where the GaN well width is on the order of 1.0 nm, which indicates that three bound states exist in the well. The bound energy levels in the quantum wells were obtained from the transmission probability calculated by using the propagation matrix method (also know as transfer matrix method). The values of the calculated energy levels were found to be in good agreement with the measured values. The quantum structures were characterized using photoluminescence, optical absorption, TEM, AFM, and XRD techniques. The carrier concentrations in various samples were measured using the electrochemical capacitance-voltage technique. Modulation of the carrier concentration was not observed due to the diffusion of the dopants from the well to the barrier, which occurs during the high growth temperature of 800 - 850 oC. Furthermore, devices were fabricated using a reactive ion etching technique and the device photoresponse was measured using a Fourier-transform spectrometer. The dark current and the photoresponse of the devices were measured in the temperature range of 4.2-300K. For most devices tested, the photoresponse was obtained at low values of the bias voltages. In some cases the photoresponse was observed at zero bias voltage, which is an indication of the presence of photovoltaic effect
2:45 PM - I13.2
Enhancement of Light-extraction Efficiency in Light-emitting Diodes by Optimized Scattering Properties of Nanoparticle-loaded Encapsulants.
Frank Mont 1 , Hong Luo 2 , Jong Kyu Kim 1 , E. Fred Schubert 1 2
1 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Show Abstract3:00 PM - I13.3
Whispering-gallery Modes in GaN-based White-light-emitting Diode Lamps with Remote Phosphor.
Hong Luo 1 , Jong Kyu Kim 2 , E. Fred Schubert 2 , Jaehee Cho 3 , Cheolsoo Sone 3 , Yongjo Park 3
1 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Electrical, Computer, and Systems Engineering Department, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Photonics Program Team , Samsung Advanced Institute of Technology, Suwon Korea (the Republic of)
Show Abstract3:15 PM - I13.4
Emission Mediated by Cross Coupling of Surface Plasmons from Metal/GaN and Metal/ZnO for the Fabrication of Top-emitting Light Emitting Diodes.
Dang Yuan Lei 1 , Hock Chun Ong 1
1 Physics Dept., The Chinese Univ. of Hong Kong, Hong Kong China
Show Abstract3:30 PM - I13.5
Ultrathin AlN/GaN Heterojunctions by MBE for THz Applications.
Yu Cao 1 , Debdeep Jena 1
1 Electrical Engineering, Univ. of Notre Dame, Notre Dame, Indiana, United States
Show AbstractDyakanov and Shur have proposed that both gated and ungated 2D electron gases satisfying certain criteria can be used for generating terahertz radiation1. The basic requirements are that a) the electron density in the 2DEG should be large enough for ensuring that the electron-electron scattering mean-free path is much shorter than the distance between the contacts to ensure a viscous, fluid-like flow, and b) the mobility should be high enough such that the possible plasma modes are not strongly damped. To sustain plasma oscillations for a reasonably large number of periods, the plasma frequency and momentum scattering time (related to mobility) product should be much larger than 1. Since the plasma frequency increases with the 2DEG density, AlN/GaN heterojunction offer an attractive route to the generation of high-frequency THz radiation. The absence of alloy scattering in these binary heterojunctions that can result in high mobilities, coupled with the very high electron densities achievable (ranging from 1E13 cm-2 to 4E13 cm-2), provides a motivation for studying the growth and transport properties of ultrathin AlN/GaN heterojunctions. In addition, the location of the 2DEG very close to the sample surface will further enhance the emission by reducing losses incurred by absorption in the barrier layer. The plasma frequency achievable can reach ~100THz for 2DEG densities approaching 3e13/cm2, relaxing the requirements on the transport properties (mobility of ~1000cm2/Vs is needed, which is achievable at room temperature). The lattice mismatch between AlN and GaN limits the critical thickness for coherently strained AlN growth on GaN to ~5nm2. A series of AlN/GaN samples were grown by Nitrogen-source RFMBE with different substrate temperatures. The fluxes of Ga and Al were fixed at 1.56E-7 Torr and 1.48E-7 Torr respectively. The substrate temperatures were varied from 730-800C. 3nm AlN layers were grown on an undoped GaN layer, starting from a semi-insulating GaN substrate. The structural and electronic transport properties of the ultrathin AlN/GaN structures were characterized. AFM measurements show smooth surface morphologies with atomic steps and dislocation terminations, with surface roughness RMS in the 0.5nm range. Measured Hall mobilities were around 530 cm2/Vs (room temperature) and 860 cm2/Vs (77K), and 2DEG sheet carrier concentration in the 2.5e13 cm-2 range was achieved. The 2DEG is located only ~4nm below the sample surface and the transport properties show marked improvement with increasing growth temperatures. The extremely high carrier density, and improvements in transport properties with increasing growth temperature indicates that ultrathin AlN/GaN heterojunctions can provide an attractive route to future THz device applications. 1. Phys. Rev. Lett. 71, 2465 (1993) and Appl. Phys. Lett. 87, 111501 (2005)2. Appl. Phys. Lett. 77, 3998 (2000)
4:00 PM - I13:Devices
BREAK
I14: Electronic Device I
Session Chairs
Thursday PM, November 30, 2006
Room 311 (Hynes)
4:30 PM - I14.1
The Influence of Device Structure on High-electric-field Effects and Reliability of AlGaN/GaN HFETs.
Weiwei Kuang 1 , Robert Trew 1 , Griff Bilbro 1 , Yueying Liu 1
1 , North Carolina State University, Raleigh, North Carolina, United States
Show Abstract4:45 PM - I14.2
GaN/AlGaN Enhancement Mode HEMT's with in-situ Passivation.
Joff Derluyn 1 , Steven Boeykens 1 2 , Kai Cheng 1 , Dongping Xiao 1 , Anne Lorenz 1 , Krishnan Balachander 1 , Marianne Germain 1 , Ronnie Belmans 2 , Gustaaf Borghs 1
1 MCP/NEXT - ART, IMEC, Leuven Belgium, 2 ESAT/INSYS, KUL, Leuven Belgium
Show Abstract5:00 PM - I14.3
AlGaN/GaN-sensors for Monitoring of Enzyme Activity by pH-Measurements.
Gabriel Kittler 1 , Armin Spitznas 1 , Benedikt Luebbers 1 , Vadim Lebedev 1 , Dennis Wegener 2 , Michael Gebinoga 1 , Frank Weise 1 , Andreas Schober 1 , Oliver Ambacher 1
1 Institute for Micro- and Nanotechnologies, Technical University Ilmenau, Ilmenau Germany, 2 , Institute of Physical High Technology Jena, Jena Germany
Show AbstractThe enzyme activity and reaction kinetics of a lipase assay were monitored by continuous measuring of pH-value with novel optimized GaN-based sensors.
Group-III nitrides are pyroelectric materials, i.e. they show spontaneous and piezoelectric polarization. The difference of polarization within an AlGaN/GaN-heterostructure leads to local fixed polarization charges screened by the accumulation of free carriers close to the interface [1]. The carrier density of the two-dimensional electron gas (2DEG) is very sensitive to any manipulation of surface potential. Therefore this heterostructure can be used to develop sensors for the detection of ions, gases, and polar liquids [2]. The optical transparency of the GaN-based sensors can be used to combine electrical with optical measurements with wavelengths above 360 nm.The sensitivity of AlGaN/GaN-heterostructures caused by changing the surface potential were already demonstrated for H+-ions [3], cell action potential [4], and even for immobilized proteins [5]. GaN-based sensors were calibrated with different buffer solutions. At room temperature the sensitivity of pH-sensors is around 59 mV/pH showing Nernstian behavior. In order to determine the sensitivity and the operation point of the sensors IDS-URef-characteristics were measured at different pH-values. The measured reference potential showed a linear dependence from the pH-value.We present the monitoring of an enzymatic lipase assay and of reaction kinetics by continuously measuring the pH-value. Lipases are the most versatile biocatalysts used for many biotransformation reactions such as alcoholysis, acidolysis, and hydrolysis. In our experiments lipase reacted with 4-nitrophenyl caprylate producing caprylic acid. The changing of pH is measured for different enzyme concentrations resulting in different reaction velocities. The AlGaN/GaN-sensors are well suited for these measurements with a total reaction volume of about 35 µl.Another application is monitoring the enzymatic release of acetate by histone deacetylases (HDAC) by measuring changes in pH in order to identify new inhibitors for these actual and promising target enzymes in cancer therapy. Utilisation of this pH-sensor would give the chance to identify these inhibitors directly without other (bio-)chemical reactions in a homogeneous format by continuously monitoring the target enzyme. This work was supported by the Thuringian ministry of culture (TKM) and the European Union (EFRE program: B 678-03001, 6th framework program: GaNano NMP4-CT2003-505614).
References:
[1] O. Ambacher et al., J. Appl. Phys. 85, 3222 (1999).
[2] R. Neuberger, G. Müller, O. Ambacher, and M. Stutzmann, phys. stat. sol. (a) 185, 85 (2001).
[3] G. Steinhoff, M. Hermann, W. J. Schaff, L. F. Eastman, M. Stutzmann, and M. Eickhoff, Appl. Phys. Lett. 83, 177 (2003).
[4] G. Steinhoff et al., Appl. Phys. Lett. 86, 033901 (2005).
[5] B. S. Kang et al., Appl. Phys. Lett. 87, 023508 (2005).
5:15 PM - I14.4
Application of n+ GaN Cap in AlGaN/GaN HEMT
Yi Pei 1 , Dario Buttari 1 , Tomas Palacios 1 , Likun Shen 1 , Rongming Chu 1 , Nick Fichtenbaum 1 , Lee McCarthy 1 , Sten Heikman 1 , Arpan Chakraborty 1 , Stacia Keller 1 , Steven DenBaars 1 2 , Umesh Mishra 1
1 ECE Department, Univeristy of California, Santa Barbara, Santa Barbara, California, United States, 2 Materials Department, Univeristy of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractAlGaN/GaN high electron mobility transistors (HEMTs) have significantly advanced during the past years leading to exceptional high frequency performance. Record f_T (180 GHz) and f_MAX (230 GHz) have been reported . Further reduction of parasitic resistances will lead to even better high frequency performance from these devices. In this paper we will report on the design space, technology and device results of the use of n+ GaN cap layers to reduce the access resistances and achieve non-alloyed ohmic contacts in AlGaN/GaN HEMTs.AlGaN/GaN HEMT samples with 500 Angstroms n+ GaN cap were grown by metal-organic chemical vapor deposition. The main challenge in these samples with n+ GaN cap layers is to achieve good communication between the GaN cap and the 2-dimensional electron gas (2DEG). The direct growth of a heavily n-type GaN cap layer on top of AlGaN/GaN HEMTs results in large conduction band discontinuities and polarization fields at the heterointerfaces. To mitigate this problem, in this paper we propose the use of Si-delta doping with a concentration of 10^13 cm-2 at the n+ GaN/AlGaN interface and 2×10^12 cm-2 at the AlGaN/GaN interface.During the processing of the ohmic contacts, Ti/Ni/Au was used as metal stack. The non-alloyed ohmic contact resistance significantly improves if the surface oxide is removed prior to the deposition with a BCl3 plasma etch. A contact resistance as low as 0.4 Ωmm was measured with the n+ cap removed from the source to drain region. After the sample is annealed, even lower contact resistance is achieved. To study the communication between the n+ cap layer and the 2DEG, the n+ layer was removed from small trenches between TLM patterns and the sheet resistance was compared. The results demonstrate excellent communication between the n+ cap layer and the channel which renders a sheet resistance of 100 ohm/sq.The processing of transistors in samples with n+ cap layer is difficult due to the trade off between gate leakage and gate-to-n+ cap layer distance. Different technologies have been studied in this work, including gate realignment, dielectric sidewalls and differential lateral etch. The use of a selective etch during the gate recess to assure the correct removal of the n+ cap layer below the gate has also been necessary.The DC performance in n+ GaN HEMTs was measured (I_ds=1.1 A/mm at V_g=1V). 25% lower access resistance was achieved compared to a standard AlGaN/GaN HEMT sample. f_T of 23 GHz and f_max of 55 GHz were measured in unpassivated devices.In conclusion, a highly doped GaN cap has been used to significantly decrease the access resistances and to achieve non-alloyed ohmic contacts in AlGaN/GaN HEMTs. These results show the great potential of these structures for improving high frequency performance, though further optimization of gate leakage is required, .This work has been partially funded by the ONR CANE and MINE projects, monitored by Dr. H. Dietrich and Dr. P. Maki.
5:30 PM - I14.5
High performance Enhancement-mode AlGaN/GaN Junction Heterostructure Filed Effect Ttransistors with p-type GaN Gate Contact.
Motoaki Iwaya 1 2 , Takahiro Fujii 1 2 , Satoshi Kamiyama 1 2 , Hiroshi Amano 1 2 , Isamu Akasaki 1 2
1 Department of Materials Science and Engineering, Meijo University, Nagoya Japan, 2 21st-Century COE Program “Nano-Factory”, Meijo University, Nagoya Japan
Show Abstract5:45 PM - I14.6
Electrical Detection of Deoxyribonucleic Acid Hybridization With AlGaN/GaN High Electron Mobility Transistors
Byoungsam Kang 1 , Jaujiun Chen 1 , Fan Ren 1 , Stephen Pearton 2
1 Chemical Engineering, University of Florida, Gainesville, Florida, United States, 2 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show AbstractAu-gated AlGaN/GaN High Electron Mobility Transistor structures were functionalized in the gate region with 3'-thiol modified oligonucleotides. This serves as a binding layer to the AlGaN surface for hybridization of matched target DNAs. X-ray photoelectron spectroscopy (XPS) shows that immobilization of thiol modified DNA covalently bonded with gold on the gated region. Hybridization between probe DNA and matched or mismatched target DNAs was shown by electrical measurements. The HEMT drain-source current showed a clear decrease of 115 µA as this matched target DNA was introduced to probe DNA in the surface, showing the promise of DNA sequence detection approach for biological sensing.
I15: Poster Session II
Session Chairs
Friday AM, December 01, 2006
Exhibition Hall D (Hynes)
9:00 PM - I15.1
Magnetic and Optical Properties of Eu-doped GaN
J. Hite 1 , G. Thaler 1 , J. Park 2 , A. Steckl 2 , J. Zavada 3 , C. Abernathy 1 , Stephen Pearton 1
1 Materials, Univ.Florida, Gainesville, Florida, United States, 2 Nanoelectronics Laboratory, University of Cincinnati, Cincinnati, Ohio, United States, 3 Electronics Division, US Army Research Office, Research Triangle Park, North Carolina, United States
Show AbstractThere is continued strong interest in the properties of rare-earth doped wide bandgap nitrides for their potential application in visible lasers that can be grown on Si substrates. In particular, the large bandgaps of GaN, AlN and their alloys allow emission of higher energy rare earth transitions that are otherwise absorbed in smaller bandgap host materials. Therefore, these materials may have application in visible displays or in white light systems that employ color-combining techniques. GaN films were doped with Eu during growth at 800C by MBE, with the Ga cell temperature held constant at 470C. All samples were post-annealed at 675C. The films exhibited strong photoluminescence in the red (620 nm) whose absolute intensity was a function of the Ga flux during growth, which ranged from 3-5.4x10-7 Torr. The maximum PL intensity was obtained at a Ga flux of 3.6x10-7 Torr. The samples showed room temperature ferromagnetism for the samples grown with the lowest Ga fluxes, with saturation magnetization of ~0.5 emu/cm3, consistent with past reports where the Eu was found to be predominantly occupying substitutional Ga sites. XRD showed the presence of small concentrations of EuGa phases under all of our growth conditions.
9:00 PM - I15.10
High Light-Extraction Efficiency in GaInN Light-Emitting Diode with Pyramid Reflector
Jingqun Xi 1 , Hong Luo 1 , Jong Kyu Kim 2 , E. Fred Schubert 2 1
1 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Insititute, Troy, New York, United States, 2 Department of Electrical, computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractA new type of reflector with a 3-dimensional pyramidal structure consisting of an array of SiO2 pyramids and a reflective Ag layer is used to increase the light-extraction efficiency of a GaInN LED. The multi-quantum well GaInN LEDs used in this study are grown by metal-organic vapor phase epitaxy and have a peak emission wavelength of 400 nm. An array of pyramids is fabricated on p-type GaN by plasma enhanced chemical vapor deposition of a 1.2 μm thick SiO2 layer followed by wet chemical etching. Each SiO2 pyramid has a base width of 3.5 μm and a slope angle of 25 degree. The spacing between pyramids is 2.5 μm and serves for ohmic contact formation. Ag is deposited on top of the SiO2 pyramids and used as a reflective layer. A reference multi-quantum well GaInN LED with planar Ag reflector is fabricated for comparison. The GaInN LED employing the pyramid-patterned Ag reflector is demonstrated to have a 14% higher light-output compared to the LED with a planar Ag reflector. The higher light output of the pyramid-patterned LED is attributed to enhanced light-extraction efficiency enabled by the change in propagation direction of light rays when reflected by the 3-dimensional structure of the pyramid reflector. Due to total internal reflection, GaInN LEDs with planar reflector have an escape cone angle of 0 degree-23.6 degree. A GaInN LED with 3-dimensional pyramid reflector is shown to have an additional escape cone of 25.5 degree – 36.0 degree, that is enabled by the 3-dimensional pyramid structure. Optical ray-tracing simulations are performed on both the GaInN LED with a pyramid reflector and the LED with a planar Ag reflector. In the simulation, the pyramid’s base length is lb = 3.5 μm, and the spacing is s = 2.0 μm. The square-shaped 100-μm-thick GaInN LED chip has a lateral dimension of 300 μm × 300 μm. The simulation results show that the pyramid reflector, with optical pyramid slope angle of 30 degree, increases the LED’s bottom emission by 27.6%, and total emission by 14.1%, consistent with our experimental results. The current-spreading length for the p-type GaN beneath each SiO2 pyramid is calculated to be few micrometers, which is comparable with the base dimension of a single SiO2 pyramid. This shows our GaInN LED with pyramid reflector has very reasonable current spreading beneath the SiO2 pyramid.
9:00 PM - I15.11
Electrical Properties, Deep Levels Spectra and Luminescence of Undoped GaN/InGaN Multi-quantum-well Structures as Affected by Electron Irradiation.
Alexander Polyakov 1 , Nikolai Smirnov 1 , Anatoliy Govorkov 1 , Alexander Markov 1 , Jong Baek 2 , Cheul-Ro Lee 3 , In-Hwan Lee 3 , Nikolai Kolin 4 , Denis Merkurisov 4 , Vladimir Boiko 4 , Lars Voss 5 , Stephen Pearton 5
1 , Institute of Rare Metals, Moscow Russian Federation, 2 , Center of Technology Strategy Development, Korea Photonics Technology Institute, Gwangju Korea (the Republic of), 3 , School of Advanced Materials Engineering and Research Institute of Advanced Materials Development, Chonbuk National University, Chonju Korea (the Republic of), 4 , Obninsk Branch of Federal State Unitary Enterprise, Karpov Institute of Physical Chemistry, Obninsk Russian Federation, 5 , Department of Materials Science and Engineering, University of Florida, Gainesville, Gainesville, Florida, United States
Show Abstract9:00 PM - I15.12
Temperature Dependence of the Quantum Efficiency in Green and Deep Green GaInN/GaN Light Emitting Eiodes.
Yufeng Li 1 2 , Wei Zhao 1 2 , Yong Xia 1 2 , Mingwei Zhu 1 2 , Jayantha Senawiratne 1 2 , Theeradetch Detchprohm 1 2 , E. Fred Schubert 1 2 3 , Christian Wetzel 1 2
1 Future Chips Constellation, Rensselaer Polytechnic Institute, Rensselaer Polytechinic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechinic Institute, Troy, New York, United States, 3 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechinic Institute, Troy, New York, United States
Show Abstract9:00 PM - I15.13
Estimation of Junction Temperature in Operating Light Emitting Diodes.
Md. Shahrukh Sakhawat 1 , Arindra Guha 1 , Okechukwu Akpa 1 , Ping Hagler 2 , Dake Wang 2 , Minseo Park 2 , Kalyankumar Das 1
1 Department of Electrical Engineering, Tuskegee University, Tuskegee, Alabama, United States, 2 Department of Physics, Auburn University, Auburn, Alabama, United States
Show Abstract9:00 PM - I15.14
Performance of InGaN/GaN Light-emitting Diodes with Different Active Region Structures.
Yun-Li Li 1 , Yun-Chorng Chang 2
1 Graduate Institute of Electro-Optical Engineering, National Taiwan University , Taipei Taiwan, 2 Institute of Electro-Optical Science and Engineering, National Cheng-Kung University, Tainan Taiwan
Show Abstract9:00 PM - I15.15
Recombination Dynamics at Dislocations in GaInN-based Light-Emitting Diodes
Jayashis Das 1 2 , Jong Kyu Kim 1 3 , Yangang Xi 1 2 , E. Schubert 1 2 3 , Peter Mensz 4
1 The Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Department of Electrical Computer and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 4 High Pressure Institute, Polish Academy of Sciences, Warsaw Poland
Show AbstractThe dynamics of radiative and non-radiative recombination near dislocation line charges in III–V nitride semiconductors is investigated by the analysis of carrier concentrations in close proximity to dislocations. It is shown that the analysis provides significant insight into efficiency of GaInN light-emitting diodes (LEDs); specifically, the well-known “efficiency droop” found at high current densities in III–V nitride LEDs can be fully explained by the model presented. The product of electron concentration (n) and hole concentration (p), which is directly proportional to the radiative recombination rate, has, near a dislocation line, a distinct dependence on position. We consider two cases: In the first case the electronic states are outside the forbidden gap [1] and in the second case, the states are inside the forbidden gap [2]. Independently, we also consider low-excitation and high-excitation conditions representing low and high injection-current densities. It is shown that for low excitation densities in n-type GaN with a negative line charge caused by a dislocation line, the np product decreases in the vicinity of a dislocation line, particularly when the electronic states are located outside the forbidden gap. The decrease is the result of the very dissimilar dependence of the electron and hole concentration on the magnitude of the potential perturbation caused by the dislocation line charge. This clearly shows that dark spots found in cathodoluminescence spectroscopy in the vicinity of dislocations can be an indication of the absence of radiative recombination rather than the presence of non-radiative recombination (as commonly assumed).We find a distinctly different behavior at high excitation densities, where the np product in the vicinity of a dislocation line depends on position to a much weaker degree than at low-excitation densities. The approximate constancy of the np product with position (at high excitation densities) enables a strong influence of a dislocation on recombination, namely a much greater strength of non-radiative recombination.We will discuss the results in relation to the previously-reported efficiency droop that is demonstrated in GaInN light-emitting-diodes grown on a sapphire substrate when injected with a high current density. We quantify the efficiency droop for several devices and show that our model can fully explain the long-standing puzzle of the efficiency droop.References:[1]D.C. Look and J. R. Sizelove, “Dislocation Scattering in GaN” Physical Review Letters, 82, 1237, (1999)[2] P. J. Hansen, Y. E. Strausser, A. N. Erickson, E. J. Tarsa, P. Kozodoy, E. G. Brazel, J. P. Ibbetson, U. Mishra, V. Narayanamurti, S. P. DenBaars, and J. S. Speck, “Scanning capacitance microscopy imaging of threading dislocations in GaN films grown on .0001. sapphire by metalorganic chemical vapor deposition” Applied Physics Letters, 72, 2247,(1998)
9:00 PM - I15.16
Analysis of the Schottky Barrier Height of W2B-based Rectifying Contacts to p-GaN.
Luc Stafford 1 , Lars Voss 1 , Steve Pearton 1 , Jau-Jiun Chen 2 , Fan Ren 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract9:00 PM - I15.17
Investigation of Boride based High Thermal Stability Contacts to AlGaN/GaN HEMT.
Rohit Khanna 1 , S. Pearton 1 , T. Anderson 2 , L. Stafford 1 , F. Ren 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Department of Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract At present there is great interest in wide-bandgap GaN and related materials because of their exciting applications in visible and ultraviolet (UV) lasers and light-emitting diodes (LEDs) for display and data storage, high electron mobility transistors (HEMTs) for high-temperature and high-power electronics, and solar-blind UV detectors. One of the remaining obstacles for commercialization of GaN HEMTs power amplifiers is the development of more reliable and thermally stable Ohmic contacts. In this work, a novel metallization scheme for source and drain contact (Ti/Al/TiB2/Ti/Au) and also for gate metallization to AlGaN/GaN HEMT using a high temperature boride was studied using contact resistance, scanning electron microscopy and Auger Electron Spectroscopy measurements and electrical characterization of HEMT. TiB2 was chosen based on the study done on different boride schemes and choosing the one which was most stable and had minimum contact resistance. A minimum contact resistance of 7x10-6 Ω.cm2 was achieved for W2B based scheme at an annealing temperature of 800°C. For TiB2 it was of 2x10-6 Ω.cm2 at 800°C and 900°C and 8x10-6 Ω.cm2 for CrB2 at 800°C. Contact resistances were found to be essentially independent of measurement temperature, indicating that tunneling plays a dominant role in the current transport. The outdiffusion of Ti to the surface at temperatures of ~500°C, and at 800°C the onset of intermixing of Al within the contact was found to occur. By 1000°C, the contact showed a reacted appearance and AES showed almost complete intermixing of the metallization. The variation in saturated drain-source current of HEMTs as a function of aging time at 350°C for different gate metallurgies using Ti/Al/TiB2/Ti/Au as the Ohmic contacts was studied. The results for conventional metallurgies (Ti/Al/Pt/Au for the drain and source and Pt/Au for the gate) were also studied for comparison. Boride-based Ohmic contacts clearly show a much more stable evolution upon aging time than the conventional Ti/Al/Pt/Au contacts. The results show promise for operation in environment at around 350°C, which simulates the type of device operating temperature that might be expected for operation of GaN-based power electronic devices.
9:00 PM - I15.18
Solid-state Reaction-optimization for Ohmic Contacts on AlGaN/GaN HEMTs
Fitih Mohammed 1 2 , Liang Wang 1 2 , Ilesanmi Adesida 1 2 3
1 Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show AbstractAlGaN/GaN HEMTs are uniquely suited for applications in microwave power amplification due to the properties of III-Nitride materials. Low-resistance Ohmic contacts are needed for enhanced performance of these devices. In this paper, we present the processing of excellent Ohmic contacts, and demonstrate a thermally-activated solid-state reaction optimization process for control and enhancement of contact properties. In the design of Ohmic contacts, metals such as Ti and Ta are of interest due to their reaction with N atoms from the AlGaN layer. The N-vacancies, thus created, have the effect of rendering the epilayer beneath n-type doped and enhancing the tunneling probability of carriers. A comparative investigation of Ti/Al/Mo/Au and Ta/Al/Mo/Au schemes has been carried out to examine the efficacy of nitride-formation reactions in enabling low-resistance Ohmic contact formation. Lower contact resistances have been obtained for Ti/Al/Mo/Au than Ta/Al/Mo/Au. Microstructural analyses using Auger electron spectroscopy (AES) and Transmission electron microscopy (TEM) have revealed a high degree of complexity in the intermetallic and interfacial reactions, and distinct types of contact formation mechanisms. While current transport is limited to tunneling in Ta/Al/Mo/Au, in Ti/Al/Mo/Au, there is an added low Schottky barrier assisted mechanism via reaction products containing TiN that penetrate into and make direct contact with the 2DEG at the AlGaN/GaN interface. Optimally annealed contacts contained a nonuniform and aggressive interfacial TiN and minimal TaN formation. This is attributed to the lower heat of formation for TiN than TaN. Microstructural analyses have also indicated that AlAux formation takes place in both schemes despite the usage of Mo to prevent the indiffusion of Au and outdiffusion of Al. This presents the possibility of inducing reactions of Al and Au with other elements, such as Si, to explore low-temperature eutectic alloy formation. Electrical characteristics of Si-containing Ti/Al/Mo/Au schemes show that Si-incorporation induces a significant reduction in the contact resistance and makes possible a wide processing temperature window. The insertion of Si prior to the deposition of the metal stacks has also enhanced the interfacial thermal stability and surface morphology of the contacts. Characterization of these Si-containing schemes indicated that the intermetallic and interfacial solid-state reactions and Ohmic contact formation mechanisms vary considerably depending on the distribution and total thickness of the inserted Si layers. Cases of suppression of TiN formation, AlN interfacial layer formation, Al-Au-Si solid solution formation, and/or MoSix and TiSix formation have been observed. These results demonstrate a novel approach for controlling and optimizing interfacial solid-state reactions in order to obtain low-resistance Ohmic contacts, large processing window, and high-temperature thermal stability.
9:00 PM - I15.19
Electronic Structure of Fe in GaN.
Piotr Boguslawski 1 , Jerry Bernholc 2 , Agnieszka Wolos 3 , Hanka Przybylinska 1 3 , Wolfgang Jantsch 3 , Michal Bockowski 4 , Izabella Grzegory 4 , Sylwester Porowski 4
1 Institute of Physics , Polish Academy of Sciences, Warsaw Poland, 2 Center for High Performance Simulation and Department of Physics, North Carolina State University, Raleigh, North Carolina, United States, 3 Institute of Semiconductor and Solid State Physics, Johannes Kepler University, Linz Austria, 4 Institute of High Pressure Physics, Unipress, Warsaw Poland
Show AbstractFe, as an impurity in GaN, introduces both a magnetic moment and deep electronic defect levels. Doping of GaN with Fe is thus recently considered in the context of obtaining room-temperature ferromagnetism as well as fabricating semi-insulating GaN substrates.In order to investigate the nature of Fe in GaN, single-crystal GaN samples doped with 5*1018 cm-3 Fe ions have been grown by the high-pressure technique. The crystals are n-type due to unintentional co-doping with oxygen. In optical absorption measurements the presence of a photoionization band with an onset at the optical energy of 1.9 eV is observed. The band is identified as due to the electronic transition from the Fe2+/3+ level to the GaN conduction band. The analysis of the shape of the band versus the temperature reveals large lattice relaxation effects, resulting in relaxation energy for the above transition of 0.6 eV. The thermal energy, i.e., the location of the Fe2+/3+ level with respect to the bottom of GaN conduction band, is determined as 1.3 eV. The effects of bond relaxation are discussed. The electronic structure of Fe in GaN was studied within the density functional theory using the generalized gradient approximation. The impact of the Fermi energy on the levels of Fe is analyzed by considering Fe4+, Fe3+, and Fe2+ configurations. These three charge states correspond to the cases of p-codoped, intrinsic, and n-codoped samples, respectively. Both the crystal field splitting and the exchange energy of Fe levels is well accounted for. Fe introduces a triplet in the band gap. The change of the charge state from Fe4+ to Fe2+ increases the triplet energy from 0.5 to 0.9 eV, while the exchange splitting between the spin-up and spin-down states increases from 0.8 to 1.6 eV. The spin-forbidden origin of the observed intra-center optical transitions of Fe3+ at 1.3 and 2.0 eV is confirmed. The calculations agree well with results of optical studies of bulk GaN:Fe. The experimentally determined location of the thermal Fe2+/3+ level is well accounted for. Significant atomic relaxation effects and their role in determining the energy levels in GaN:Fe are also recognized in the calculations. The relaxations induce energy changes of about 0.5 eV, accompanied with changes of bond lengths of a few percent. Thus, inclusion of relaxations is necessary for a consistent interpretation of the experimental data.
9:00 PM - I15.2
Optical and X-ray Experimental Probes of Rare Earth Nitride Film Band Structures
Tony Bittar 1 , Ben Ruck 2 , Andrew Preston 2 , Simon Granville 2 , Joe Trodahl 2 3 , James Downes 4 , Kevin Smith 5
1 , Industrial Research Limited, Lower Hutt New Zealand, 2 MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington New Zealand, 3 Laboratoire de Céramique, École Polytechnique Fédérale de Lausanne, Lausanne Switzerland, 4 Physics Department, Macquarie University, Sydney, New South Wales, Australia, 5 Physics Department, Boston University, Boston, Massachusetts, United States
Show AbstractThursday, 11/30ReinstatedPoster I15.2Optical and X-ray Experimental Probes of Rare Earth Nitride Film Band Structures. Tony Bittar1, Ben J Ruck2, Andrew Preston2, Simon Granville2, Joe Trodahl2,3, James Downes4 and Kevin Smith5; 1Industrial Research Limited, Lower Hutt, New Zealand; 2MacDiarmid Institute for Advanced Materials and Nanotechnology, Victoria University of Wellington, Wellington, New Zealand; 3Laboratoire de Céramique, École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland; 4Physics Department, Macquarie University, Sydney, New South Wales, Australia; 5Physics Department, Boston University, Boston, Massachusetts.Calculations of the rare earth nitride band structures predict variously metallic or semiconducting ground states, and a strong dependence of these and their magnetic properties on the lattice constants. Experimental confirmations of these band structures are surprisingly rare, due in large part to their instability in the presence of air. Here we will report optical reflection-transmission and ellipsometric measurements on rare-earth nitride films grown with passivating capping layers by deposition both in a pure nitrogen atmosphere and in the presence of nitrogen ions. The data reveal band-gaps in the visible, with no evidence of an intraband Drude absorption at low energy, thus confirming their semiconducting nature. The direct band gaps probed by this technique lie in the range of 1.0 -2.5 eV at ambient temperature. The optical studies have been supported in some cases by x-ray absorption and emission spectroscopies, which directly probe the density of empty and filled states.
9:00 PM - I15.20
500 K operation AlGaN/GaN HFETs with a large current and a high breakdown voltage.
Hiroshi Kambayashi 1 , Jiang Li 1 , Nariaki Ikeda 1 , Seikoh Yoshida 1
1 , The Furukawa Electric Co., Ltd., Yokohama, Kanagawa, Japan
Show AbstractAlGaN/GaN heterojunction field effect transistors (HFETs) have outstanding features such as being able to operate under high-temperature, high-frequency, and high-power conditions, and it is therefore expected to find wide applications in power conversion devices, etc. In this paper, it is reported that we demonstrated a large current operation AlGaN/GaN HFET with a low-on state resistance and a high breakdown voltage operation at 500 K. A heterostructure of undoped Al0.22Ga0.78N (30 nm) / GaN (3000 nm) / buffer layer was grown on a sapphire substrate using a metal organic chemical vapor deposition (MOCVD) method. In order to improve the HFET performance, the reduction of on-state resistance is necessary, and for that purpose, it is required to be decreased contact resistance between the ohmic electrode and the the AlGaN layer. We previously used selective area growth (SAG) technique to decrease the contact resistance of HFET. But in this case, the breakdown voltage was lower due to the roughness of interface between an AlGaN layer and an SAG layer. In order to improve the breakdown voltage and the on-state resistance, we have applied a new ohmic contact using a Ti/AlSi/Mo metallization on the AlGaN layer without an SAG technique. In this metallization, the contact resistance was lower to be 1/3 compared with that of a Ti/Al. Furthermore, we investigated the dependence between the breakdown voltage and the distance from the gate electrode to the drain electrode (Lgd) by fabricating small scale (gate length = 400 μm) AlGaN/GaN HFETs. As the Lgd was increased, the breakdown voltage was increased, resulting in obtaining 1000 V in the case of the Lgd of 15 μm.We next fabricated the large scale AlGaN/GaN HFET using Ti/AlSi/Mo ohmic electrode and applying the Lgd of 15 μm. In order to suppress the increase of on-resistance, the gate width of 240 mm was selected. The gate length was 2 μm and the distance from the gate electrode to the source electrode (Lgs) was 3 μm. The maximum drain current of over 50 A was obtained at room temperature and also, that of over 25 A was obtained at 500 K. The minimum on-resistance was less than 70 mohm at room temperature and 160 mohm at 500 K, respectively. The off-state breakdown voltage was obtained about 800 V at room temperature and about 600 V at 500 K, although Si-based FETs can not operate in such a high temperature. These results suggest that an AlGaN/GaN HFET is very promising for a very low loss and high efficiency device.
9:00 PM - I15.21
Reduction of the Dispersion by Passivation of in-situ Silicon Nitride of AlGaN/GaN HEMTs.
Anne Lorenz 1 2 , Joachim John 2 , Joff Derluyn 2 , Stefan Degroote 2 , Maarten Leys 2 , Kai Cheng 1 2 , Marianne Germain 2 , Gustaaf Borghs 1 2
1 , Katholic University of Leuven, Leuven Belgium, 2 , IMEC, Leuven Belgium
Show Abstract9:00 PM - I15.22
Ion-Implanted GaN/AlGaN/GaN HEMTs with Extremely Low Gate Leakage Current
Kazuki Nomoto 1 , Tomoyoshi Mishima 2 , Masataka Satoh 1 , Tohru Nakamura 1
1 EECE, Hosei University, Koganei, Tokyo, Japan, 2 , Hitachi Cable, Tuchiura, Ibaraki, Japan
Show Abstract In this paper, we demonstrate the realization of compatibility of extremely low gate-leakage current and low source resistance with novel ion-implanted (I/I) GaN/AlGaN/GaN HEMTs without any recess etching process. The AlGaN/GaN HEMTs have been studied as candidates for high power devices for the RF and power electronics systems. However, there are gate leakage current and current collapse as a major problem of the device with this AlGaN/GaN structure. The leakage current originates from piezoelectrically induced polarization charge appears on the lattice-strained AlGaN. Although a practical method to decrease gate leakage current and current collapse is to grow the GaN cap layer onto the AlGaN, precise etching technology is needed to reduce source/drain resistance of GaN/AlGaN/GaN double-heterojunction barriers. In this study, we decreased source/drain resistance without etching by forming the heavily doped source/drain regions by using ion implantation. The ion implantation is one of the most indispensable technologies for impurity doping especially in silicon based integrated circuits. Recently, it is widely recognized that the ion implantation is an effective technology to the improvement of the GaN device characteristics, and the characteristics become also more than equivalent as compared with the conventional AlGaN/GaN HEMT with a gate recess structure. A 2 um thick undoped GaN buffer layer, a 25 nm undoped Al0.25Ga0.75N layer and a 5 nm undoped GaN layer was grown on a sapphire substrate by MOVPE. Silicon ions are implanted into source/drain regions at a dose of 1 x 1015 /cm2 at the energy of 80 keV through a 30 nm thick SiNx layer. This process was followed by the activation annealing at 1200 oC for 2 min. The SiNx layer was removed using diluted HF and a SiNx layer for surface passivation was deposited again. Source/drain ohmic contacts were formed by depositing Ti/Al (50/200 nm) layers, followed by the annealing at 600 oC for 3 min. Finally, gate schottky contacts were formed by depositing Ni/Al (50/200 nm) layers. Devices with 2 um gate length and 10 um gate width were tested. Gate-source and gate-drain spacing were 1 um. DC characteristics of I/I AlGaN/GaN HEMTs and I/I GaN/AlGaN/GaN HEMTs were measured. Maximum drain current of 527 mA/mm at Vg= 1 V and maximum transconductance of 84 mS/mm were obtained for I/I GaN/AlGaN/GaN HEMTs, while those of I/I AlGaN/GaN HEMTs were 379 mA/mm and 100 mS/mm, respectively. The reversed gate leakage current for I/I GaN/AlGaN/GaN HEMTs was only 0.4 nA at 100 V, while the same current was observed at 8 V for I/I AlGaN/GaN HEMTs.
9:00 PM - I15.23
Low-voltage Avalanche in AlGaN Multi-quantum Wells.
Shengkun Zhang 1 , Xecong Zhou 1 , Wubao Wang 1 , Robert Alfano 1 , A m Dabiran 2 , A. Osinsky 2 , A m Wowchak 2 , B. Hertog 2 , C. Plaut 2 , P p Chow 2
1 , City College of New York, New York, New York, United States, 2 , SVT Associates, Inc., Eden Prairie, Minnesota, United States
Show AbstractAlGaN avalanche devices are difficult to be realized due to the large band gaps of AlGaN materials. Since extremely high electric fields are required to accelerate carriers in conduction band to reach threshold energy for impact ionization from valence band, avalanche in AlGaN diodes requires a voltage as large as 100 V in normal case.In this work, avalanche and avalanche luminescence have been observed in AlGaN multi-quantum wells (MQWs) under voltages down to 9 V. The investigated device is a AlGaN p-i-n diode. The active i-region consists of Al0.1Ga0.9N/Al0.15Ga0.85N MQWs. Strong interband avalanche luminescence from the Al0.1Ga0.9N active layers was observed when the applied bias was larger than 9 V. This indicates that the impact ionization coefficient of electrons is greatly enhanced in these Al0.1Ga0.9N/Al0.15Ga0.85N MQWs comparing to AlGaN bulk materials. Polarization-induced electric fields in the Al0.1Ga0.9N well layers are believed to be responsible for the enhancement of the ionization coefficient. In a control sample that has higher defect density, the electroluminescence was dominated by long-wavelength emissions, which results from impact ionizations of the defect levels.
9:00 PM - I15.24
Characterization of (Sc2O3)x(Ga2O3)1-x as a Gate Dielectric for GaN MOS Diodes.
Mark Hlad 1 , Cammy Abernathy 1 , Steve Pearton 1 , Brent Gila 1 , Jerry Thaler 1
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract9:00 PM - I15.26
n-AlGaAs/p-GaAs/n-GaN HBTs Exhibiting Current Gain of 10 Prepared by Wafer Fusion.
Chuanxin Lian 1 , Huili (Grace) Xing 1 , Chad Wang 2
1 , U. of Notre Dame, Notre Dame, Indiana, United States, 2 , U. of California, Santa Barbara, Santa Barbara, California, United States
Show AbstractAlGaAs/GaAs/GaN heterojunction bipolar transistors (HBTs) have been proposed and demonstrated recently, by direct wafer fusion, to harvest the high quality p-type GaAs and the large bandgap properties of GaN for high speed high power devices. [1,2] Employing a lower fusion temperature of 600 C and inserting a UID setback layer, a current gain of ~ 2 was obtained. [3] In this paper, we show the influence of different fusion conditions and etch stop layers on the device performance. By improving the fusion process and device structures, we demonstrate fused HBTs with current gain of up to 10.All AlGaAs/GaAs samples were grown by MBE, consisting of a 0.5 μm AlGaAs etch stop layer followed by Si heavily doped GaAs layer for emitter contacts, graded Al0.3GaAs:Si (~ 5e17 cm-3) emitter, and a 100 nm carbon doped GaAs (~ 1e19 cm-3) p-base capped with a 30 nm GaAs:C (~ 1e17 cm-3) setback layer. The GaN samples were grown by MOCVD on c-plane sapphire, consisting of 1 μm GaN:Si (~ 5e16 cm-3) collector on 1.5 μm GaN:Si (~ 4e18 cm-3). After solvent clean in acetone and isopropanol, both the AlGaAs/GaAs and GaN samples were soaked in NH4OH to remove the oxide. The samples were then immediately joined in methanol in order to prevent oxidation. After a uniaxial pressure of 5 Mpa was applied at room temperature, two wafers underwent a one-hour annealing in a N2 atmosphere at ~ 500 mTorr and the temperature varied from 550 C to 650 C. After the wafer fusion, the GaAs substrate was removed by spray etch in H2O2:NH4OH (= 30:1), followed by a selective removal of the AlGaAs etch stop layer in HF. It was observed the resultant GaAs thin films were as rough as > 10 nm when Al0.98GaAs etch stop was used. On the other hand, when employing Al0.9GaAs as etch stop, a much smoother film was obtained with an rms of ~ 1 nm. In comparison, the rms values of as-grown GaAs and GaN wafers are 0.3 and 0.5 nm, respectively. X-ray and TEM were also used to characterize the fusion interface and the resultant thin film.Mesa structure HBTs were fabricated and tested. It shows that a lower fusion temperature tends to render better electronic operations. The HBTs fused at 550 C show a current gain of ~ 5-10 and those fused at 600 C and 650 C exhibit similar gains ~ 2-3. The ideality factors of the p-GaAs/n-GaN base/collector junctions fall between 1 and 2. The temperature dependent device characterization was also carried out, in comparison with as-grown AlGaAs/GaAs HBTs with similar structures, which will be presented.[1] Estrada et al., APL 83(3): P. 560-562, 2003[2] Estrada et al., Int. J. of High Speed Electronics and Systems 14(1): P. 265-284, 2004[3] Estrada et al., MRS Proc. 798, Y10-20-1, 2004
9:00 PM - I15.27
Influence of Overheating Effect on Transport Properties of AlGaN/GaN Heterostructures
Andriy Kurakin 1 , Svetlana Vitusevich 1 , Mykhailo Petrychuk 2 , Hilde Hardtdegen 1 , Serhiy Danylyuk 1 , Alexander Belyaev 3 , Norbert Klein 1
1 ISG-2, Forschungszentrum Juelich, Juelich Germany, 2 , Taras Shevchenko National University, Kiew Ukraine, 3 , V.Lashkaryov Institute of Semiconductor Physics, NASU, Kiew Ukraine
Show AbstractAlGaN/GaN heterostructures can operate at very high power in dc and rf regimes due to the superior properties of III-nitride materials. At the same time, the higher level of dissipated power causes higher overheating in the structures. Considering the fact that the temperature is a driving force for aging processes in devices, it is clear that the investigations of thermal effects in 2DEG of GaN-based structures are of great importance. Additionally, such studies result in a better understanding of the transport features which affect device performance, and allow us to determine the conditions under which hot-electron effects play the dominant role in electron transport.In this report we focus on thermal effects in transmission line model (TLM) patterns. The experimental results and numerical simulations of self-heating effects in TLM patterns processed on heterostructures with different layer design (different Al mole fraction of barrier layer, different substrates) are analyzed. The GaN-based heterostructures were grown by MOCVD. One of the investigated samples consists of a nucleation layer of AlGaN (16% Al), an undoped GaN buffer layer and an AlGaN (33%) undoped barrier layer. This type of structure was formed on sapphire and SiC substrates. Additionally, another two types of structures were grown on sapphire substrate: with wide bandgap barrier layer (with Al mole fraction of 75%), and with a thin AlN spacer layer (5nm) in between the AlGaN barrier layer (23 nm) and the GaN buffer layer (1300 nm). All samples were processed with TLM patterns with standard Ti/Al/Ti/Au contact metallization and annealed for 40s at 800° C. The conducting channel of the devices has a width W = 100 μm with intercontact lengths L of 5, 10, 15, 20, 25, 30, 35 μm. The average overheating temperature over the active channel area for each structure type is estimated. The strong influence of the Al mole fraction of the barrier layer and also the substrate type of the structure on noise and transport properties is revealed and analyzed. It was shown that the implementation of wide bandgap barriers and high thermal conductance substrates allows us to improve the overall performance of the structures significantly. Optimal conditions for the observation of hot-electron effects are determined.
9:00 PM - I15.28
Persistent Photoconductivity in High-mobility AlxGa1-xN/AlN/GaN Heterostructures Grown by Metal-organic Vapor-phase Epitaxy.
Necmi Biyikli 1 , Cagliyan Kurdak 2 , Umit Ozgur 1 , Xiangfeng Ni 1 , Yi Fu 1 , Hadis Morkoc 1
1 Electrical & Computer Engineering, Virginia Commonwealth University, Richmond, Virginia, United States, 2 Department of Physics, University of Michigan, Ann Arbor, Michigan, United States
Show Abstract9:00 PM - I15.29
Electrical Activation Studies of Silicon Implanted AlxGa1-xN.
Timothy Zens 2 1 , Mee-Yi Ryu 1 , Yung Kee Yeo 1
2 SNHC, AFRL, Hanscom AFB, Massachusetts, United States, 1 ENP, AFIT, Dayton, Ohio, United States
Show AbstractElectrical activation studies of silicon implanted AlxGa1-xN grown on sapphire substrates were conducted as a function of ion dose, anneal temperature, and anneal time. Due to increasing demand for robust electrical and optical systems it is imperative to understand the optimal methods for repairing damage done to group-III nitrides during ion implantation. Silicon ion doses of 1x1013, 5x1013, and 1x1014 cm-2 were implanted in AlxGa1-xN samples with aluminum x = 0.1 and x=0.2 at an energy of 200 keV at room temperature. The average depth of implantation was 150 nm and the films were grown 1 µm thick by MBE. The samples were proximity cap annealed at temperatures from 1100 to 1350 °C and anneal times of 20 to 40 minutes with a 500 Å thick AlN cap in a nitrogen environment. The Hall coefficient and resistivity were measured using room temperature Hall effect measurements. From this data the Hall mobility, sheet carrier concentration, and electrical activation efficiencies were calculated. These studies showed that although lower mobilities are observed in Al-rich AlxGa1-xN , higher activation efficiencies can be achieved because the substrates can endure higher annealing temperatures. Activation efficiencies of 95 to 99% were achieved for Al0.2Ga0.8N samples having doses of 5x1013 and 1x1014 cm-2 after annealing at 1350 and 1300 °C, respectively, for 20 minutes. The highest mobility for Al0.2Ga0.8N was 75.7 cm2/V●s for the sample having an ion dose of 1x1014 cm-2 and annealed at 1350 °C for 20 minutes. On the other hand, after annealing at 1250 °C for 20 minutes, 87% activation efficiency was achieved for Al0.1Ga0.9N implanted with 1x1014 cm-2 silicon ions. The largest observed mobility was 89 cm2/V●s for Al0.1Ga0.9N implanted with 1x1014 cm-2 and 5x1013 cm-2 silicon ions and annealed at 1250 °C for 20 minutes and at 1200 °C for 40 minutes, respectively.
9:00 PM - I15.3
Evaluation on Crystal and Optical Properties of AlN:Er Prepared by RF magnetron sputtering method
Shin-ichiro Uekusa 1 , Takahiko Ohno 1 , Hiroshi Miura 1
1 School of Science and Technology, Meiji University, Kawasaki, kanagawa, Japan
Show AbstractThe Er that is rare earth element causes luminescence at 1.54 μm, which is a low loss transmission window in silica-based fibers used in optical communications. Moreover, it is known that the temperature quenching of the luminescence of Er becomes smaller with the wide band gap of the host material. We report on the Photoluminescence (PL) characteristic and X-Ray Diffraction (XRD) of AlN:Er thin films which is grown by RF reactive magnetron co-sputtering method. All the films were deposited by RF reactive magnetron co-sputtering method from Al target (99.999%) and Er chips (99.99%) in the nitrogen gas (99.9998%) atmosphere. All depositions were achieved with a discharge power of 250W, a total pressure of 0.05 Pa, and the deposition times were one hour. We applied annealing for 30 minutes in the temperature range from 400 to 1000 oC in a nitrogen gas (99.999%) atmosphere with an infrared rays lamp. PL spectra of AlN:Er were measured using the 325nm line of a He-Cd laser at 15K. Consequently, we observed PL spectra around 1.5μm. The strong peak wave length luminescence at 1538nm is based on the intra-4f emitting centers of Er. We report systematically the experimental results of PL and XRD.
9:00 PM - I15.30
Traps in Si-doped AlxGa1-xN Grown by Molecular Beam Epitaxy on Sapphire Characterized by Deep Level Transient Spectroscopy.
Mo Ahoujja 1 , Said Elhamri 1 , Michael Hogsed 2 , Yung Kee Yeo 2 , Robert Hengehold 2
1 Physics, University of Dayton, Dayton, Ohio, United States, 2 ENP, Air Force Institute of Technology, WPAFB, Ohio, United States
Show Abstract9:00 PM - I15.31
Investigation of Electrical Properties in Si Ion Implanted GaN Layer as A Function of Dose and Energy.
Masataka Satoh 1 , Tomohiro Saitoh 1 , Kazuki Nomoto 1 , Tohru Nakamura 1
1 Dept. of EECE & I.B. Tech., Hosei University, Koganei, Tokyo Japan
Show AbstractThe ion implantation technique is a useful method to fabricate the various conductive regions in the GaN devices. We have reported that the ion implantation technique is able to be applied to the fabrication of the active layer and the considerable reduction of the contact resistance in the electrode region in MESFET[1,2]. However, there are a few papers about the application of ion implantation technique to the fabrication of active layer in GaN devices except for the isolation regions[1-3]. In this study, electrical properties of n+ layer in GaN produced by Si ion implantation are investigated as a function of Si dose and energy. Sample in this study was undoped GaN grown on sapphire with an AlN buffer layer. Thickness of GaN layer was 2 μm. Si ions are implanted at the energy ranging from 30 to 120 keV and at dose from 1 x 1014 to 5 x 1015 /cm2. The implanted samples were annealed at 1200 oC for 10 s in N2 gas flow with a cap film of SiNx with a thickness of 50 nm. The sheet resistance and sheet carrier concentration are evaluated by means of Van der Pauw and Hall effect measurement. Ohmic electrodes are formed by depositing Ti(50)/Al(200nm) layer on corners of sample and subsequently annealing at 600 oC for 5 min in N2 gas flow. For the constant Si ion energy of 30 keV, lowest sheet resistance of 56 Ω/sq. is obtained for Si ion dose of 2 x 1015 /cm2. In this sample, the sheet carrier concentration is estimated to be 1 x 1015 /cm2, which corresponds to the electrical activity of 50 % for implanted Si. However, by increasing Si ion dose, sheet carrier concentration seems to be saturated at the range from 0.8 to 1 x 1015 /cm2 for Si dose above 2 x 1015 /cm2 (electrical activity decreases). Sheet resistance is increased to 80 Ω/sq with slight decrease of mobility of electrons. The experimental results describe above are consistent to the published papers[4].For the constant Si ion dose of 2 x 1015 /cm2, the samples implanted by 50, 80 and 120 keV Si ion show also the sheet carrier concentration of 1 x 1015 /cm2 as well as sample implanted by 30 keV Si. In this study, the electrical activity of implanted Si depends on only Si ion dose rather than the energy and the maximum Si concentration at projected range (6 x 1020 /cm3 for energy of 30 keV, 2 x 1020 /cm3 for 120 keV). The mobility of electrons decreased from 110 to 80 cm2/Vs as Si ion energy increased from 30 to 120 keV. The decrease in mobility may be attributed to the residual defects even after annealing at 1200 oC, which do not affect the activity of implanted Si impurity. The investigation of structural properties is in progress using ion scattering and transmission electron microscope.[1] K. Nomoto et al., MRS Proceedings Vol. 892 (in press).[2] N. Itoh et al., MRS Proceedings Vol. 892 (in press).[3] H. Yu et al., IEEE Electron Dev. ED-26, 283(2005). [4] J.A. Fellows et al., Appl. Phys. Lett. Vol. 80, 1930(2002).
9:00 PM - I15.32
Structural Properties of AlxIn1-xN films Grown by Metalorganic Chemical Vapor Deposition
Ryo Kajitani 1 , Misaichi Takeuchi 2 1 , Koji Kawasaki 1 , Yoshinobu Aoyagi 1 2
1 , Tokyo Institute of Technology, Yokohana, Kanagawa, Japan, 2 , RIKEN, Wako, Saitama, Japan
Show AbstractWe studied on the structural properties of thin AlxIn1-xN layer grown on c-plane sapphire substrate with GaN buffer layer by metalorganic chemical vapor deposition (MOCVD) using X-ray diffraction (XRD) measurements and Atomic force microscopy (AFM). AlxIn1-xN (x=0.88-0.98) layer was grown at 725oC. The surface morphology and Al composition of AlxIn1-xN layer strongly depend on the V/III molar ratio, and the roughness of the surface morphology of the AlxIn1-xN layer was decreased as the Al molar fraction decreased. However, the FWHM of XRD (002) rocking curve of these AlxIn1-xN layer remains equal to the value of 140-160 arcsec, and these values were smaller than that of the value of GaN layer, 280 arcsec. These results of XRD (0002) rocking curve are very similar to AlN films. Therefore, the AlxIn1-xN layers tended to be grown in the three-dimensional growth mode.
9:00 PM - I15.33
Polarization Induced p-type Doping in N-face graded AlGaN-GaN p-n junctions.
John Simon 1 , Huili Xing 1 , Debdeep Jena 1
1 E.E., University of Notre Dame, Notre Dame, Indiana, United States
Show AbstractIII-V nitrides display high polarization fields due to their wurtzite crystal structure. Recent developments have demonstrated the use of the spatially varying polarization in graded heterostructures to induce 2- and 3-D electron slabs in nitride heterojunctions1, implying that mobile electrons can be induced without impurity dopants. This same method can be applied to produce regions of mobile holes. Regions of high p-type conductivity are essential to bipolar and optical devices2. High activation energies of acceptor dopants have limited the performance of many nitride based devices. By using polarization-induced p-type doping, the absence of activation energy and impurity scattering can improve p-type conductivity. The technique we demonstrate offers a novel and attractive route to efficiently generate n- and p-type doping of high-Al composition AlGaN layers that are important in UV-emitters and HBTs. Before these layers can be utilized in the base layer of an npn HBT, a p-n junction is studied where the p-layer is polarization-doped without acceptor atoms. Graded AlGaN-GaN p-n junctions were grown by RF-MBE on (0001bar) n+ GaN substrates. A 200nm n-GaN was grown, followed by a 200nm 0-30% linearly graded AlGaN layer, and a 5nm Al0.3Ga0.7N:p++ cap layer for ohmic contacts. The graded AlGaN layer was coherently strained as determined by X-ray diffraction measurements. Samples with Mg-doped GaN layers were also grown on both Ga and N-face substrates as control samples to compare to the polarization-doped junction. These growth conditions typically produce n and p doping levels of ~7x1017cm-3 and ~5x1017cm-3 respectively. The junctions were processed by etching mesas using reactive ion etching, and Ni/Au contacts were deposited and annealed in a N2/O2 ambient at 640oC for 30sec for ohmic contact to the p-type layers. Al/Au contacts were used for ohmics to the n-type etched areas. Transport measurements were performed on both types of p-n junctions (with polarization-doped and acceptor doped p-layers). The current across both junctions exhibited rectification. The on/off ratio for the graded junction at 4V/-4V was found to be ~3x105, which is ~104 times larger than the acceptor-doped junctions. Ideality factors ranging from 2-4 were observed. Temperature-dependent IV’s were performed on all three structures. The leakage current in all three junctions exhibited thermionic behavior with an activation energy of ~150meV. The forward bias current remained relatively constant with changing temperature for the graded junction, indicating the fundamentally different nature of minority carriers in the polarization-doped junctions. This bodes well for devices that undergo large temperature gradients. This indicates that polarization-induced doping may be an attractive alternative route for solving various doping problems plaguing III-V nitrides. 1.Appl. Phys. Lett. 88(4), 042109 (2006) 2.J. Phys.: Condens. Matter 13 (2001) 7139
9:00 PM - I15.34
Au/Ni/GaN/SiNx Nanonework/sapphire Schottky I-V Characteristics.
Jinqiao Xie 1 , Hadis Morkoç 1
1 , Virginia Commonwealth University, Richmond, Virginia, United States
Show Abstract9:00 PM - I15.35
Development of Aluminum Nitride/Platinum Stack Structures for Enhanced Piezoelectric Response
Adam Kabulski 1 , Sridhar Kuchibhatla 1 , Vincent Pagan 1 , Parviz Famouri 1 , Dimitris Korakakis 1
1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, West Virginia, United States
Show Abstract Aluminum nitride (AlN) films have been developed for piezoelectric and high temperature applications, but the piezoelectric response is still much lower than that of more common piezoelectric materials such as lead zirconate titanate (PZT). However, a method of increasing the apparent piezoelectric coefficient d33 of aluminum nitride has been explored by depositing stack structures composed of aluminum nitride and platinum. These stack structures were created by depositing a thin, ~50nm, metal layer in between thicker, ~150-250nm, layers of the piezoelectric film. Platinum was chosen as the metal layer as well as the topside electrical contact because of an increased piezoelectric response resulting at the interface of aluminum nitride and a high work function metal. The thickness of the aluminum nitride films was also varied for each stack structure. An electric field was applied across the structure and displacements were measured using a Laser Doppler Vibrometer. The structures were found to have two distinct regions of piezoelectricity with the piezoelectric coefficient becoming much greater when the applied electric field exceeded 300kV/cm. For the maximum electric field of 400kV/cm, d33 values were observed to be as high as 8.0pm/V, more than twice that of the theoretical limit for polycrystalline aluminum nitride (3.9pm/V). The influence of the thickness of the aluminum nitride layers on the piezoelectric response of the structure has also been explored. In microelectromechanical systems (MEMS) applications, bimorph and trimorph structures are often developed to strengthen the structure or as protective barriers. In this case, the structures have been developed to not only protect the piezoelectric film, but also as a method of engineering band alignments. A model will be discussed that explains the band alignments as well as the relationships between the aluminum nitride/platinum interfaces and the thickness of the piezoelectric film on the enhanced piezoelectric effect.
9:00 PM - I15.36
Electroreflectance Spectra of InGaN/AlGaN/GaN p-n-Heterostructures.
Alexander Yunovich 1 , L. Avakyants 1 , M. Badgutdinov 1 , P. Bokov 1 , A. Chervyakov 1 , S. Shirokov 1 , E. Vasileva 2 , A. Feopentov 2 , F. Snegov 2 , D. Bauman 2 , B. Yavich 2
1 Department of Physics, M.V.Lomonosov Moscow State University, Moscow Russian Federation, 2 , “Svetlana-Optoelectroniks” JSC, S.-Petersburg Russian Federation
Show Abstract9:00 PM - I15.37
Scanning Electroluminescence Microscopy of Blue InGaN Light Emitting Diodes on Si-substrate: Current Injection Inhomogeneity and Local Heating.
Lars Reissmann 1 , Juergen Christen 1 , Thomas Hempel 1 , Armin Dadgar 1 2 , Alois Krost 1 2
1 Institute of Experimental Physics, Otto-von-Guericke-University, Magdeburg Germany, 2 , AZZURRO Semiconductors AG, Magdeburg Germany
Show Abstract9:00 PM - I15.38
Characterization of Epitaxial GaN/Si Using Capacitance Spectroscopies.
Steven Smith 1 , John Roberts 2 , P. Rajagopal 2 , J. Cook 2 , E. Piner 2 , K. Linthicum 2
1 Materials & Manufacturing Directorate, Air Force Research laboratory, Wright-Patterson AFB, Ohio, United States, 2 , Nitronex, Raliegh, North Carolina, United States
Show AbstractLayers of GaN deposited on Si substrates have been studied using Thermal Admittance Spectroscopy (TAS), Deep Level Transient Spectroscopy (DLTS), and Optical Admittance Spectroscopy (OAS). Transparent front-side contacts were used to facilitate the optical measurements, while both front-side and front+back-side contacts were used to study the electrically active levels in the bandgap and differentiate between those levels in the substrate and those in the GaN layer. The optical measurements revealed the interesting phenomenon of negative persistent photo conductance (PPC) at room temperature in some of the specimens when the illumination photon energy was less than the bandgap. At lower temperatures, below 100 K, the negative aspect was diminished, but the time constant was still long. Double beam methods were used to help characterize the state(s) responsible for the PPC. A shallow level at EC – 0.051 eV was found in all the specimens using TAS. In some specimens this peak was asymmetric, indicating more than one level near this energy. Deeper levels were also seen in the high-temperature portion of the spectra, but were poorly resolved in some specimens. DLTS measurements were used to study the electrically active deep levels not observable by TAS.
9:00 PM - I15.39
Vertically Increasing Well Thickness and In Content in GaInN MQW's due to V-shaped Pits.
Heiko Bremers 1 , Lars Hoffmann 1 , Daniel Fuhrmann 1 , Uwe Rossow 1 , Andreas Hangleiter 1
1 Institute of applied physics, Technical Unversity of Braunschweig, Braunschweig Germany
Show Abstract9:00 PM - I15.4
Photoluminescence Characteristics of InGaN/InAlGaN Multiple Quantum Wells for Blue LEDs
Sung-Bum Bae 1 , Ho-Sang Kwack 1 2 , Yong-Hoon Cho 2 , Chang-Soo Kim 3 , Kyu-Seok Lee 1
1 IT Convergence & Components Laboratory , Electronics and Telecommunications Research Institute, Daejeon Korea (the Republic of), 2 Department of Physics, Chungbuk National University, Cheongju Korea (the Republic of), 3 Division of Advanced Technology, Korea Research Institute of Standard and Science, Daejeon Korea (the Republic of)
Show AbstractBlue light emitting diodes(LEDs) based on InGaN/GaN multiple quantum wells(MQWs) with a p-AlGaN carrier-blocking layer can be degraded due to large differences in the lattice parameter and the thermal expansion coefficient of the epi-layer. To overcome these problems, various schemes for the active layer of GaN-based LEDs have been subjects of recent researches. Here, we report on photoluminescence properties of InGaN/InAlGaN MQWs grown on sapphire substrates by metal-organic chemical vapor deposition. The samples for this study consist of a 30-nm-thick GaN buffer, a 2-μm-thick undoped GaN, and 5 periods of 3/15-nm-thick In0.14Ga0.86N/InAlGaN MQWs. A series of samples having InAlGaN barriers with different compositions were prepared and investigated by using photoluminescence(PL), X-ray diffraction, and atomic force microscopy. For In0.14Ga0.86N/GaN MQWs, the TMGa and the TMIn flows for the growth of In0.14Ga0.86N wells were 40 and 20 μmoles, respectively, and the TMGa flow for the growth of GaN barriers was 40 μmoles. The center wavelength of the PL line originated from In0.14Ga0.86N MQWs is 453 nm at room temperature, and its full width at half maximum is 19 nm. In0.14Ga0.86N/InxGa1-xN MQWs whose barrier layers were grown at TMIn flows of 2.5, 3.8, 5.0 and 7.5 μmoles have indium compositions of the barrier x = 0.039, 0.055, 0.073, and 0.089, respectively, and the center wavelengths of the PL emission from the MQWs are 453, 452, 450 and 445 nm, respectively. The blue shift with the increase of the indium composition of barriers can be explained by the effect of piezoelectric polarization to the quantum confinement. In0.14Ga0.86N/AlyGa1-yN MQWs( y = 0.025 and 0.05) grown at TMAl flows of 1 and 2 μmoles for AlGaN barriers show PL spectra with the center wavelength of 461 and 471 nm, respectively. The piezoelectric and spontaneous polarization in AlGaN plays an important role for a red shift of about 18 nm with increasing the Al composition from 0 to 0.05. On the other hand, the PL of In0.14Ga0.86N/InAlGaN MQWs with InAlGaN grown at a TMIn flow of 7.5 μmoles and a TMAl flow of 1 μmole have a center wavelength of 449 nm, showing a small blue shift of 4 nm from the PL peak of the InGaN/GaN sample, whereas the PL intensity of the InGaN/InAlGaN MQWs is enhanced in comparison with that of InGaN/GaN MQWs. These results demonstrate that InGaN/InAlGaN MQWs are good candidates for blue LEDs.
9:00 PM - I15.40
Real Time Spectroscopic Ellipsometry Investigation of the Synthesis of Mg-Doped GaN Using Plasma-assisted Molecular Beam Epitaxy.
Tong-Ho Kim 1 , Soojeong Choi 1 , Inho Yoon 1 , Changhyun Yi 1 , April Brown 1 , Maria Losurdo 2 , Giovanni Bruno 2 , Akihiro Moto 3
1 Electrical and Computer Engineering, Duke University, Durham, North Carolina, United States, 2 Institute of Inorganic Methodologies, IMIP-CNR, Bari Italy, 3 , Innovation Core SEI, Inc, Santa Clara, California, United States
Show AbstractAchieving high quality Mg-doped GaN is crucial for the development of nitride-based optoelectronic and electronic devices, such as light emitting diodes, lasers, and heterojunction bipolar transistors. Plasma-assisted molecular beam epitaxy (PAMBE) provides some advantages for Mg doping over metalorganic vapor phase epitaxy (MOVPE) since the formation of compensating Mg complexes is lower and sharper doping profiles are possible. One of the most important issues is the role of excess Ga on the growth surface of GaN during Mg doping and how this relates to polarity inversion that leads to roughening of the morphology, increasing defect densities, and lowered incorporation of Mg. We have studied the relationships between Mg doping parameters using PAMBE, specifically Mg flux and Ga/N ratio, on the incorporation, morphology, and polarity inversion using in-situ SE. SE spectra of the Mg:GaN pseudodielectric function recorded in real time during Mg:GaN growth show a red shift of the fundamental absorption edge with increasing Mg incorporation and Mg flux, which is supported by post-growth second ion mass spectroscopy (SIMS) measurements of Mg concentration. This result shows that monitoring the energy position of the fundamental absorption edge by real time SE spectra is a good means of probing variations of band gap due to variation of the incorporated Mg concentration. In fact, we observed that the in-situ SE spectra can measure a gradual reduction in Mg incorporation, observed also with SIMS, due to Mg accumulation at the sample surface. Furthermore, in order to investigate the role of excess Ga during Mg doping, we studied three Mg doping cases for growth of Mg:GaN on an HVPE grown GaN template using a fixed Mg BEP of 4e-9 Torr and Ga BEP 18% higher than the droplet boundary condition, i.e. (1) direct Mg:GaN growth, (2) Mg:GaN growth after first depositing 6.8 ML on the surface of the GaN template, and (3) Mg:GaN growth after growth of a 25 nm thick undoped GaN layer. We found the direct Mg:GaN growth led to the polarity inversion from Ga-polar to N-polar. This result is verified by a 3x3 reflection high electron energy diffraction (RHEED) reconstruction at low temperature and atomic force microscopy (AFM) and chemical characterization. Correspondingly, the SE data monitored during the direct Mg:GaN case show different kinetic and pseudodielectric function spectra from the other cases. This indicates that the excess Ga layer and its thickness is critical to maintaining the growth kinetics of Mg:GaN epilayer after an undoped GaN growth We also present the effects of growing with Ga above the Ga droplet boundary on the Mg incorporation. In addition, we found that the Ga/N ratio under Ga-rich condition was the most important parameter in controlling the surface morphology through the real time SE monitoring of roughening, which was corroborated by post-growth measurements of AFM.
9:00 PM - I15.41
Characterisation of Epitaxial Lateral Overgrown GaN by Electron Backscatter Diffraction Correlated with Cross-Sectional Cathodoluminescence Spectroscopy.
Francis Sweeney 1 , Carol Trager-Cowan 1 , Paul Edwards 1 , Angus Wilkinson 2 , Ian Watson 3
1 SUPA,Physics, University of Strathclyde, Glasgow, Lanarkshire, United Kingdom, 2 Materials, University of Oxford, Oxford, Oxfordshire, United Kingdom, 3 SUPA, Institute of Photonics, University of Strathclyde, Glasgow, Lanarkshire, United Kingdom
Show AbstractManufacturers of nitride based LEDs and LDs are seeking ways to increase device efficiency and longevity. To achieve this dislocation densities in nitride films have to be reduced; typically a GaN epilayer grown heteroepitaxially on a sapphire substrate can have a dislocation density as high as 1010cm-2. A common growth method for reducing dislocation densities in GaN is Epitaxial Lateral Overgrowth (ELO). Using this method a 103 reduction in the dislocation density in the ELO regions above the mask can be achieved.In this presentation we shall report on our strain investigations of a just-coalesced 4μm thick ELO GaN epitaxial layer. In our study we used two independent techniques: Cathodoluminescence (CL) hyper-spectral imaging and Electron Backscatter Diffraction (EBSD). CL allows us to attain a wealth of information about the optical properties of a crystalline semiconductor with sub-micron resolution. The width and position of a peak in a luminescence spectrum is sensitive to strain, crystallinity, defects, doping and free carrier concentrations. EBSD is a technique for probing the structural properties with high spatial resolution (~50 nm). An EBSD pattern is a direct 2-D gnomonic projection of the crystal structure and is therefore suitable for the observation of changes in the crystal structure due to strains, tilts and rotations. The EBSD strain resolution achieved in this work is ± 2×10-4.EBSD strain profiles reveal a difference of approximately 6×10-3 (3×10-3) in the a-axis (c-axis) or in-plane (out of plane) compressive (tensile) strain between the seed-wing interface and the wing-wing coalescence boundary. Using these differences a strain shift of ~ 50 meV in the CL near band-edge peak (NBEP) position is predicted. CL hyper-spectral imaging of the ELO sample was carried out in cross-section. In a CL spectrum the NBEP position is affected by strain and by carrier concentration. The CL data revealed that the NBEP changed both in position and width between the seed-wing interface and the wing-wing coalescence boundary by ~15 meV and ~ 38 meV, respectively. Previous reports show that changes in free carrier concentration in GaN between approximately 1016cm-2 and 1020cm-2 results in an increase in the NBEP width and a red-shift (to longer wavelengths) in the NBEP position. From the 38 meV increase in CL peak width observed between the seed-wing interface and the wing-wing coalescence boundary, we estimate using experimentally derived models, that the carrier concentration varies by three orders of magnitude and the resulting red shift in the NBEP due to carrier concentration variation is ~ 33 meV. Using this value to derive the shift of the CL peak due to strain alone gives a strain shift of 48 meV. This is in very good agreement with the EBSD predicted shift of 50 meV and demonstrates that by using a multi-technique approach the effects of carrier concentration and strain on the luminescence properties can be deconvoluted.
9:00 PM - I15.43
XPS Analysis of Aluminum Nitride Films Deposited by Plasma Source Molecular Beam Epitaxy.
Leland Rosenberger 1 , Ronald Baird 2 , Gregory Auner 2 , Gina Shreve 1
1 Chemical Engineering & Materials Science, Wayne State University, Detroit, Michigan, United States, 2 Electrical and Computer Engineering, Wayne State University, Detroit, Michigan, United States
Show AbstractX-ray Photoelectron Spectroscopy (XPS) has been widely used to characterize aluminum nitride (AlN) as interest in this semiconductor material has increased over the past years. Obtaining consistent chemical binding energy information has been hampered in some studies by the resolution limits of data taken with non-monochromatized x-ray sources, by the effects of sample charging on peak location/shape and by variability in the method of data curve fitting. This study attempts to address these issues by reporting on the results of the XPS depth profile of ten samples of aluminum nitride thin films prepared and analyzed under similar conditions.The aluminum nitride films were deposited using a plasma source molecular beam epitaxy system. Two samples were deposited on a Si (111) substrate and eight on c-plane (0001) sapphire. X-ray diffraction results established that all ten samples of AlN had a wurtzite crystal structure with the c-axis oriented perpendicular to the surface. The XPS depth profile spectra of the films were obtained by alternating argon ion sputter etching and multiplex data acquisition cycles using a monochromatized Al Kα x-ray source. Data collection was done at cumulative sputter times of 0, 1, 2, 5, 10, 20 and 40 minutes with a sputter rate of ~1.4 nm/min. The effects of sample charging were addressed by performing an alignment on the sample before each data acquisition cycle. The alignment was done by adjusting the output of an electron neutralizer gun in order to keep the binding energy position of the alignment peak (C 1s or N 1s) constant with respect to time during x-ray exposure. For peak fitting, all sub-peaks were fitted using a symmetric, mixed Gaussian-Lorentzian model with the percentage Gaussian remaining constant for each particular element throughout the entire analysis. For any given peak, the full width at half maximum of all sub-peaks were made equal.By using a consistent peak fitting methodology applied to all ten samples, sub-peak description was less arbitrary. The use of ten samples also permitted the incorporation of basic statistical methods in the peak fitting and analysis. Some oxygen was seen in the samples and the results show that oxygen decreases exponentially with increasing depth. All sub-peaks were observed to shift to a lower binding energy as sputtering proceeded. Bulk film conditions are seen at ~40 min sputter depth. In the bulk film the results suggest that oxygen replaces nitrogen in the lattice as substitutional point defects. The sub-peak binding energies (adjusted to C1s or Ar2p references) and their proposed chemical bond assignments are reported.
9:00 PM - I15.44
Characterization of High-Al-Content AlGaN Layers Formed During the Growth of AlN/GaN Strain Reduction Layer on Si(111) Substrate by Ammonia-MBE.
Toshimasa Suzuki 1 2 , Shota Oishi 1 , Kenta Yoshino 1 , Takanori Sasaki 1 , Seong-Woo Kim 1
1 , Nippon Institute of Technology, Miyashiro, Saitama, Japan, 2 , Epitec, Inc., Kasukabe, Saitama, Japan
Show Abstract9:00 PM - I15.45
Low-Temperature Cathodoluminescence Mapping of Green, Blue, and UV GaInN/GaN LED Dies
Yong Xia 1 2 , Theeradetch Detchprohm 1 2 , Senawiratne Jayantha 1 2 , Yufeng Li 1 2 , Wei Zhao 1 2 , Mingwei Zhu 1 2 , Christian Wetzel 1 2
1 Future Chips Constellation, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractGaInN based light emitting diodes (LEDs) play an important role as energy efficient light sources in solid state lighting. While UV, blue, and green devices are available commercially in large volumes, substantial performance improvements are anticipated, once the role of defects and inhomogeneities in the radiative recombination processes are fully understood. A controversial discussion addresses the origin of lateral light emission variations and their correlation with either of the identified defects, e.g., threading dislocations and V-defects. The wide variety of findings suggests that among a strong variation of actual growth techniques, there can be a relevant dependence on the peak wavelength of the emission. For this reason we compare data of UV, blue and green LED dies, each optimized to its individual best performance regime. In order to establish any possible correlation of defects and luminescence centers, we analyze dies of all three wavelength regions by microscopic mapping of spectroscopic cathodoluminescence and secondary electrons at variable low temperature from 7 K to room temperature. Particular effort is being placed on a quantitative analysis of the luminescence signal. Images intensities are not being scaled and offset for highest contrast as otherwise typical for imaging modes. This allows meaningful comparisons and quantitative statistical analysis, e.g. of the temperature behavior. In standard configuration we analyze image areas of (0.037 mm)2 with pixel resolution of 72 nm. By following regions of strong and weak emission we so find a maximum intensity variation of merely 20 % of the average intensity. The peak wavelength is found to vary within 0.5 %. This in particular bears relevance to the discussion of emission enhancing localization centers. Furthermore, bright and darker areas remain so throughout the temperature range studied. While for the UV range a trend is not apparent, for both, the blue and green LED dies, we find that the peak wavelength is longer in the darker spots than in the bright ones. This finding corresponds to the general trend when comparing the lower efficiency in longer wavelength green emitters to the blue ones. From this and further analysis we anticipate guidelines on how to improve further the performance of green and deep green light emitters.
9:00 PM - I15.46
Contact Metallurgy for High Al-Fraction AlxGa1-xN.
Mary Miller 1 , Suzanne Mohney 1
1 Materials Science and Engineering, Penn State University, University Park, Pennsylvania, United States
Show AbstractHigh Al-fraction AlxGa1-xN is a promising choice for short wavelength devices due to its wide band gap. One of the challenges in realizing these devices is the high resistance of the ohmic contacts to n- and p-type AlxGa1-xN as the Al fraction increases. Our group has previously studied Ni ohmic contacts to p-type Al0.45Ga0.55N. It was found that annealing at temperatures of 800°C or greater is required for ohmic contact formation1. Characterization of the metal/semiconductor interface, carried out by x-ray photoelectron spectroscopy and analytical transmission electron microscopy (TEM), showed preferential reaction of Ni with Ga, leaving behind an Al-enriched layer2. This change in composition of the AlxGa1-xN beneath the metal contact correlated to a reduced contact resistance, possibly due to the formation of Ga vacancy acceptors. We now focus on the reactions of metals that are important for ohmic contacts to n-type AlxGa1-xN, in particular for Ti- and V-based ohmic contacts. In contrast to the preferential reaction of Ni with GaN in AlxGa1-xN alloys, n-Al0.58Ga0.42N beneath Ti and V films annealed at 700, 800 and 900°C for 30s in N2 exhibited greater compositional stability. The differences in the reaction are consistent with the thermodynamic driving forces in these systems. Because of the availability of N2 in the annealing environment for nitridation of Ti and V, only modest consumption of the semiconductor through reaction with the metal films was observed using cross-sectional TEM. Reaction of the Ti films and the Al0.58Ga0.42N occurred at 700°C and became more pronounced with increasing temperature. After annealing at 900°C for 30s, a 20 nm thick Ti-Al-Ga-N layer was found beneath a thick TiN layer. Vanadium films show minimal reaction with the semiconductor when annealed at 700°C, a shallow patchy reaction after annealing at 800°C, and a 10-nm thick uniform V-Al-Ga-N phase beneath a thick layer of VN after a 900°C anneal. Cross-sections of low-resistance V/Al/V/Au contacts with a specific contact resistance of 2.6x10-4 Ohm-cm2 revealed only a shallow reaction with the semiconductor and no observable shift in the composition of the AlxGa1-xN alloy. Three phases (V-Al-Au-N, V-Al-Au and Al-Au) were found distributed throughout the contact, all of which could be detected at different locations along the contact interface. Both Au and Al were always found at the contact interface. Controlling the metallization composition to produce single-phase contacts may help further elucidate the mechanism of ohmic contact formation.1. B.A. Hull, S.E. Mohney, U. Chowdhury, and R.D. Dupuis, J. Appl. Phys. 96, 7325 (2004).2. B.A. Hull, S.E. Mohney, U. Chowdhury, and R.D. Dupuis, J. Vac. Sci. Technol. B 22, 654 (2004).
9:00 PM - I15.47
Thermal Stability of Boride-based Rectifying Contacts to p-GaN.
Lars Voss 1 , L. Stafford 1 , S. Pearton 1 , J. Chen 2 , F. Ren 2
1 Materials Science and Engineering, University of Florida, Gainesville, Florida, United States, 2 Chemical Engineering, University of Florida, Gainesville, Florida, United States
Show Abstract9:00 PM - I15.48
Active Role of the Barrier Layer in the Interfacial Reaction of Ti/Al/X/Au (X=Ni, Mo, Ti, and Ir) Ohmic Contacts to AlGaN/GaN.
Liang Wang 1 3 , Fitih Mohammed 1 3 , Ilesanmi Adesida 1 2 3
1 Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 3 Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States, 2 Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois, United States
Show Abstract9:00 PM - I15.49
Recessed Gate Processing for GaN/AlGaN-HEMTs,
Wilfried Pletschen 1 , Rudolf Kiefer 1 , Brian Raynor 1 , Fouad Benkhelifa 1 , Stefan Mueller 1 , Ruediger Quay 1 , Michael Mikulla 1 , Michael Schlechtweg 1 , Guenter Weimann 1
1 , Fraunhofer Institute of Applied Solid State Physics, Freiburg Germany
Show AbstractGaN/AlGaN HEMTs have been shown to be promising candidates for future microwave power devices. So far, most of the devices fabricated do not utilize a recessed gate configuration although it can be expected that gate recessing will improve performance significantly.For the fabrication of recessed gate GaN/AlGaN-HEMTs a dry etch process based on Cl2/SF6 using an ECR etcher has been developed to selectively remove GaN over AlGaN. In this study, etching parameters were varied over a wide range to investigate etch rate, selectivity and damage potential. Using pure chlorine GaN and AlGaN are etched equally well even for small RF powers. Small amounts of SF6 added to Cl2 (5% of total gas flow) reduce the GaN etch rate significantly while the AlGaN is not etched at all. The etch selectivity of GaN over AlGaN amounts to 15:1 and is independent of RF power in the range 40 to 84 W (DC=-72 to –120 V). Despite the low SF6 content the AlGaN barrier is not etched even for long overetch times (100%) and high RF power (84W).Recessed gate devices were fabricated on 2-inch wafers in a two-step process. First, a wide recess, typically 500 nm wider than the footprint of the gate, was prepared by electron beam lithography and Cl2/SF6 etching. The etching parameters were chosen such that bias voltage was kept rather low at a reasonable etch rate. In order to provide a fair comparison of transistor data recessed and non-recessed areas were prepared side by side resulting in a chess board pattern. In the second step, gates were defined using standard electron beam lithography and Ni/Au was used for the gate metal.Recessed gate FETs fabrictated by this process having a gatelength of 0.15 µm show cutoff frequencies of 83 and 200 GHz for fT and fmax, respectively. As expected, transconductance increases from 340 to 390 mS/mm due to the smaller channel-gate separation. Furthermore, breakdown is largely improved as compared to their non-recessed counterparts. Our study also indicates that plasma damage does not occur.More details on etching process and transistor performance will be given at the conference.
9:00 PM - I15.5
The PL Mapping Analysis Under the Condition of Selective Excitation on the Epitaxial Wafer with InGaN-LED Structure.
Kazuyuki Tadatomo 1 , Osamu Shimoike 1 , Hiromichi Noda 1 , Masahiro Hiraoka 1 , Masakazu Yoshimura 2 1 , Katsuyuki Hoshino 1
1 Graduate School of Science and Engineering, Yamaguchi University, Ube Japan, 2 , Yamaguchi Prefectural Industrial Technology Institute, Ube Japan
Show AbstractPhotoluminescence (PL) measurement is very useful to characterize epitaxial wafers with optical device structure, such as light emitting diodes (LEDs) and laser diodes (LDs). Moreover, PL mapping measurement is very useful to evaluate growth conditions including the distribution of growth temperature on the wafer and the fluctuation in gas flow in the reactor of a metal-organic vapor phase epitaxy (MOVPE) system. Because the distribution of device performance in the wafer affects the yield of device production, it is very important to evaluate and control growth conditions. Usually, to characterize the InGaN-LED wafer by the conventional PL measurement system, a He-Cd laser with a wavelength of 325 nm is applied to excite the wafer.In this study, we compared the PL mappings on a blue LED wafer using the He-Cd laser (325 nm) and a LD with a wavelength of 405 nm and a electro-luminescence (EL) mapping on the same wafer. Though the He-Cd laser mainly excites a p-GaN layer in the LED wafer, the LD selectively and directly excites the wells of multiple quantum wells (MQWs) in the wafer. After the PL mapping measurement, the wafer was fabricated into LED devices with the size of 350 μm × 350 μm. EL mapping measurement at the injection current of 20 mA using a probing machine was then carried out.We found that the regions with high EL intensity in the EL mapping were more consistent with the regions with high PL intensity in the PL mapping excited by the LD (405 nm) on the same wafer than those of PL mapping excited by the He-Cd laser (325 nm). Therefore the He-Cd laser is not suitable to characterize the MQWs or light emitting devices in the PL mapping system.These results suggest the PL mechanism under the condition of excitation using the He-Cd laser is as follows: Because the photon energy of the 325 nm wavelength (3.81 eV) is larger than the band gap of GaN (3.39 eV), the majority of pairs of electron and hole (carriers) are generated in the surface p-GaN layer. The carriers diffuse to MQWs from the p-GaN layer, and then radiatively recombine. Because some of the carriers are trapped by non-radiative recombination centers in the p-GaN layer, the PL mapping depends on not only the quality of MQWs but also the quality of the p-GaN layer. To characterize the LED wafer and to predict the device performance correctly, the PL mapping measurement must be carried out under the condition of selective and direct excitation on the wells in the MQWs.This work is partially supported by “Knowledge Cluster Initiative”, MEXT.
9:00 PM - I15.50
Vanadium Based Ohmic Contacts to n-AlGaN in the Entire Alloy Composition.
Ryan France 1 , Tao Xu 1 , Papo Chen 1 , Theodore Moustakas 1
1 Electrical and Computer Engineering, Boston University, Boston, Massachusetts, United States
Show Abstract9:00 PM - I15.51
GaAsN Thin Ffilm Growth by Chemical Beam Epitaxy with Source Gas Flow Rate Modulation.
Yoshio Ohshita 1 , Kenichi Nishimura 1 , Kenji Saito 1 , Hidetoshi Suzuki 1 , Masafumi Yamaguchi 1
1 , Toyota Technological Institute, Nagoya Japan
Show Abstract9:00 PM - I15.52
Investigation of Optical Properties of Nitrogen Incorporated Sb based Quantum Well and Quantum Dots for Infrared Sensors Application
Seongsin Kim 1 , Homan Yuen 1 , Fariba Hatami 2 , James Harris 1
1 EE, Stanford University, Stanford, California, United States, 2 Physics, Humboldt-University at Berlin, Berlin Germany
Show Abstract9:00 PM - I15.53
Low-temperature Growth of III-V Compound Semiconductors for Organic/inorganic Hybrid Device Applications.
Shanthi Iyer 1 , Liangjin Wu 1 , Kellen Gibson 1 , Jia Li 1 , Jay Lewis 2
1 E.E, North Carolina A&T State Univ., Greensboro, North Carolina, United States, 2 , Research Triangle Institute, RTP, Durham, North Carolina, United States
Show Abstract9:00 PM - I15.54
Investigation of Band Lineup in GaAsSb(N)/GaAs Strained Epilayers using X-ray Photoelectron Spectroscopy and Photoluminescence.
Sudhakar Bharatan 1 , Kalyan Nunna 1 , Shanthi Iyer 1 , Jia Li 1 , Ward Collis 1 , William Mitchel 2
1 Electrical Engineering, North Carolina A&T State University, Greensboro, North Carolina, United States, 2 , Wright-Patterson Air Force Laboratory, Wright-Patterson AFB, Ohio, United States
Show Abstract9:00 PM - I15.55
In- Situ Electrical and Mechanical Characterization of Group III- Nitride Films
David Vodnick 1 , Ryan Major 1 , James Burkstrand 1 , Peter Chow 2
1 , Hysitron, Inc., Minneapolis, Minnesota, United States, 2 , SVT Associates. Inc., Eden Prairie, Minnesota, United States
Show AbstractThe group III- nitrides are the most popular system for wide- band gap semiconductor applications and are particularly important for the fabrication of a range of optoelectronic and high- temperature/ high- power electronic devices. Successful development and integration of these materials depends heavily on the ability to quantitatively assess and tailor their electrical and mechanical properties. Although initial research was predominantly focused on electrical properties, more recently the importance of mechanical properties has become apparent to enable long-term reliability predictions.Epitaxial growth-related strain in addition to external applied stress during fabricationcreates defects such as dislocations and micro-cracks within the epilayers. Thin films are also known to differ in mechanical properties when compared to large single crystals due to the confined geometrical dimensions and the materials intrinsic defect structure.Using a novel nanoscale probe technique which utilizes nanoindentation hardware coupled with a conductive diamond indenter probe and a current and voltage source, these important electro-mechanical measurements can be obtained simultaneously.Electrical contact resistance, I-V characteristics, hardness, and modulus were correlated to film chemistry and to doping type and concentration on several film types.The measurements were made on GaN, AlGaN, and InGaN epitaxial layers grown by PA-MBE to find time dependent correlations between force, displacement, current, and voltage all measured simultaneously. The electrical behavior of these thin films as a function of mechanical deformation and indentation depth will be discussed.
9:00 PM - I15.56
Omni-directional Reflectors for GaInN Vertical-structure Light-emitting Diodes.
Roya Mirhosseini 1 , Jong Kyu Kim 1 , Hong Luo 2 , Jaehee Cho 3 , Cheolsoo Sone 3 , Yongjo Park 3 , E. Fred Schubert 1 2
1 Department of Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York, United States, 3 Photonic Program Team, Samsung Advanced Institute of Technology, Yongin, Kyungki-Do, Korea (the Republic of)
Show Abstract9:00 PM - I15.6
Cap Thickness Dependence of Photoluminescence and Phonon Satellites in InGaN/GaN Single Quantum Wells.
Lay-Theng Tan 1 , Robert W Martin 1 , Kevin P O'Donnell 1 , Ian M Watson 2
1 Physics, University of Strathclyde, Glasgow United Kingdom, 2 Institute of Photonics, University of Strathclyde, Glasgow United Kingdom
Show Abstract9:00 PM - I15.7
Resonant Energy Transfer due to Exciton Coupling in Hybrid Persovskites Conjugated to GaN Semiconductors.
Arup Neogi 1 , Jianyou Li 1 , Teruo Ishihara 2
1 Department of Physics, University of North Texas, Denton, Texas, United States, 2 Exciton Engineering Laboratory, RIKEN, Wako, Saitama, Japan
Show Abstract9:00 PM - I15.8
Effects of Surface Treatments on Optical Properties of GaN.
Gakuyo Fujimoto 1 , Hiroki Goto 1 , Katsushi Fujii 1 , Takenari Goto 1 , Cho Meoungwhan 1 , Takafumi Yao 1
1 Center for Interdisciplinary Research, Tohoku University, Sendai, Miyagi, Japan
Show Abstract9:00 PM - I15.9
Light Intensity Noise in GaInN/GaN Green Light Emitting Diodes.
Sergey Rumyantsev 1 2 , Christian Wetzel 3 , Michael Shur 1
1 Electrical, Computer, and Systems Engineering, Rensselaer Polytechnic Institute, Troy, New York, United States, 2 , Ioffe Institute of Russian Academy of Sciences, St.Petersburg Russian Federation, 3 Future Chips Constellation and Department of Physics, Rensselaer Polytechnic Institute, Troy, New York, United States
Show AbstractGaN/AlGaN and GaN/GaInN light emitting diodes (LEDs) are finding applications as a superior light source in solid-state lighting, communications, chemical synthesis, and biomedical diagnostics. An important advantage of LEDs is their potential as highly stable light sources with intensity fluctuations below those of incandescent lamps. Moroever, we find that a wavelength dependent analysis of the light noise in green GaInN/GaN LEDs reveals aspects of the carrier injection mechanism. The method is therefore suited to further optimize the performance of green and deep green LEDs.Here we study the low-frequency light noise in 515 nm green GaInN/GaN quantum well LEDs. Similar to other green LEDs, the spectral line width at room temperature is about 30-45 nm, which corresponds to (5.4-6.4) x kT. This high value is ~3 times larger than the theoretical limit when controlled by the thermal distribution of carriers. We find that the noise spectrum is predominantly a 1/f noise. A wavelength resolved measurement, however, finds important details. Most interestingly, the noise is substantially smaller for the long wavelength side of the spectrum than for the short wave length side. Overall we find that the noise level has a strong correlation with the quantum efficiency of the LED. LEDs with higher efficiency show a lower level of light intensity noise. This strongly suggests that a non-radiative recombination path may also act as a noise generating trapping site. This correlation should be most helpful to improve device performance. Next, by help of the wavelength resolved data, we find that the noise fluctuations are highly correlated in time all across the emission spectrum. This is thought to be a result of the fast spreading of carriers along the quantum wells... Altogether, our spectrally resolved noise analysis holds promise for further device improvements of green and deep green LEDs.