Controlling doping in Ga₂O₃ and AlGaO₃ alloys

The properties of gallium oxide make it particularly suitable for applications in power electronics. Ga₂O₃ has a large band gap (4.8 eV) but can also be highly n-type doped. Control of doping is crucial for devices: it should be possible to control the carrier concentrations all the way from semi-insulating to highly conductive n-type material. In addition, doping of AlGaO₃ alloys is required for the modulation-doped heterostructures used in devices. First-principles modeling, using advanced hybrid functional calculations within density functional theory, can greatly help in resolving experimental puzzles and guiding optimal doping conditions. I will present comprehensive first-principles studies of dopant impurities and of point defects and unintentional impurities that can act as compensating centers. Compensation of n-type doping may occur due to the formation of gallium vacancies, which have an unusual split-vacancy structure [1,2]. In (Al_xGa_1-x)₂O₃ alloys, controlled doping at low concentrations has proven difficult, and native-defect compensation and DX-center formation limit doping at higher Al concentrations. I will particularly focus on the role of unintentional carbon and hydrogen impurities, which are unavoidably present during growth by chemical vapor deposition [3]. Device structures also require semi-insulating layers, in which the Fermi level is pinned far from the band edges. I will discuss how this can be implemented by doping with Mg or N dopants [4]. Diffusion of these dopants during growth or subsequent processing is a major problem, which requires detailed understanding and control of point defects.



[1] J. B. Varley, H. Peelaers, A. Janotti and C. G. Van de Walle, J. Phys. Condens. Matter 23, 334212 (2011).

[2] J. M. Johnson, Z. Chen, J. B. Varley, C. M. Jackson, E. Farzana, Z. Zhang, A. R. Arehart, H.-L. Huang, A. Genc, S. A. Ringel, C. G. Van de Walle, D. A. Muller, and J. Hwang, Phys. Rev. X 9, 041027 (2019).

[3] S. Mu, M. Wang, J. B. Varley, J. L. Lyons, D. Wickramaratne , and C. G. Van de Walle, Phys. Rev. B 105, 155201 (2022).

[4] H. Peelaers, J. L. Lyons, J. B. Varley, and C. G. Van de Walle, APL Materials 7, 022519 (2019).