Available on-demand - S.EL15.01.07
MOCVD Epitaxy of β-Ga2O3 Thin Films with Record Mobilities
Zixuan Feng1,A F M Anhar Uddin Bhuiyan1,Md Rezaul Karim1,Yuxuan Zhang1,Hongping Zhao1
The Ohio State University1
β-Ga2O3 with an ultra-wide bandgap of 4.5-4.9 eV and capability of n-doping promises its applications for high power electronics. β-Ga2O3 is predicted to have high breakdown field (6-8 MV/cm) with room temperature mobility of ~200 cm2/Vs. The Baliga figure of merit (BFOM) of β-Ga2O3 for power electronics is predicted to be 2 to 3 times higher than that of GaN and SiC. More advantageously, the availability of high-quality native Ga2O3 substrates produced from melt growth techniques is critical for large scale production. High voltage (>1 kV) devices, as well as RF devices with 27 GHz cut-off frequency, have been demonstrated recently [1, 2]. Nevertheless, development of high-quality β-Ga2O3 thin film growth technology is the cornerstone for high-performance device applications. Epitaxy of β-Ga2O3 has been investigated via different methods, including MBE, MOCVD, LPCVD, PLD, ALD and etc. Recently, MOCVD grown β-Ga2O3 has exhibited record high electron mobilities in both unintentionally doped (UID)  and Si-doped films .
In this work, we continue optimizing the MOCVD β-Ga2O3 homoepitaxial process on (010) Ga2O3 crystal orientation, and expand our investigation of β-Ga2O3 MOCVD growth along different orientations including (-201), (001) and (100). Key growth parameters, including growth temperature, growth pressure, Ga/O molar ratio, and substrate preparation, were investigated. For films grown on semi-insulating Fe doped (010) Ga2O3, the epi-film exhibit low background doping. From secondary ions mass spectroscopy (SIMS) depth profile, impurities such as hydrogen (H), carbon (C), chlorine (Cl), iron (Fe) were all below the detection limit. With low intentional Si doping, we demonstrated (010) β-Ga2O3 films with controllable doping between 1016 to 1019 cm-3. From temperature dependent Hall measurements and analysis taking into account various carrier scattering mechanisms, we extracted a very low compensation level of Na < 1×1015 cm-3. Peak electron mobility reaches ~9500 cm2/Vs at T~45 K for an unintentionally doping (010) β-Ga2O3 film. We demonstrated record high room temperature mobility of ~194 cm2/Vs with n = 8×1015 cm-3. The superior transport properties of the MOCVD grown (010) β-Ga2O3 films demonstrated high purity MOCVD epitaxy process with low defects densities.
For films grown along different crystal orientations, we use scanning electron microscopy (SEM) and atomic force microscopy (AFM) to characterize the surface morphologies, which have shown significant dependence on substrate orientation. Film growth rate, doping incorporation and transport properties are investigated.
In summary, we demonstrated superb electrical transport properties from MOCVD grown (010) β-Ga2O3 thin films with high purity and low defect densities. Growth mechanisms will be investigated for films grown along other orientations. The results from this study will provide fundamental understanding of the material properties of β-Ga2O3, which determines its potential for power device applications.
Acknowledgment: The authors acknowledge the funding support from the Air Force Office of Scientific Research No. FA9550-18-1-0479 (AFOSR, Dr. Ali Sayir).
1. Z. Hu, K. Nomoto, W. Li, N. Tanen, K. Sasaki, A. Kuramata, T. Nakamura, D. Jena and H. G. Xing, IEEE Electron Device Lett. 39, 869 (2018).
2. Z. Xia, H. Xue, C. Joishi, J. F. McGlone, N. K. Kalarickal, S. H. Sohel, M. Brenner, A. Arehart, S. Ringel, S. Lodha, W. Lu, and S. Rajan, IEEE Electron Device Lett. 40, 1052 (2019).
3. Y. Zhang, F. Alema, A. Mauze, O. S. Koksaldi, R. Miller, A. Osinsky, and J. S. Speck, APL Materials 7, 022506 (2019).
4. Z. Feng, A F M A. U. Bhuiyan, M. R. Karim, H. Zhao, Appl. Phys. Lett., 114, 250601 (2019).