【Member Papers】High-field electron transport properties of α-Ga2O3

      Researchers from Hong Kong University of Science and Technology have published a dissertation titled " High-field electron transport properties of α-Ga₂O₃ " in Applied Physics Letters.

Background

      Alpha-phase gallium oxide (α-Ga₂O₃) with a corundum structure has attracted increasing attention as a promising ultra-wide- bandgap semiconductor for power electronics. Compared with the monoclinic b-Ga₂O₃ phase, α-Ga₂O₃ offers the advantage of heteroepitaxial growth on commercially available a-Al₂O₃ substrates using techniques such as Mist-CVD, enabling large-area, low-cost wafer production. Furthermore, controllable n-type doping via Sn, Si, or Ge incorporation has been experimentally demonstrated, establishing α-Ga₂O₃ as a viable platform for scalable device technologies. Previous studies on α-Ga₂O₃ have primarily focused on low-field electron transport, where polar optical phonon scattering was identified as the dominant mobility-limiting mechanism. Experimental and theoretical investigations have also reported anisotropic effective masses and phonon dispersions, suggesting a possible link between lattice dynamics and transport anisotropy. However, existing models largely rely on effective-mass approximations and simplified scattering treatments, which become inadequate under high electric fields where electrons have higher energy. A comprehensive microscopic understanding of high-field electron transport in α-Ga₂O₃—particularly the origin of transport anisotropy—remains lacking.

Abstract

      The high-field electron transport properties of alpha-phase gallium oxide (α-Ga₂O₃) under electric fields up to 1 MV/cm have been investigated using an integrated approach combining full-band first-principles calculations and Monte Carlo simulations. The electron–phonon scattering rates show strong temperature dependence at low electron energy, whereas at higher electron energy, the scattering rates become nearly temperature independent. At room temperature, the peak drift velocity reaches 2.5×10⁷ cm/s at 400 kV/cm along x and y directions, decaying to 1.0×10⁷ cm/s at 1 MV/cm. A drift velocity anisotropy emerges above roughly 200 kV/cm, with the drift velocity along the z direction consistently lower than that along x and y. Mode-resolved momentum relaxation analysis shows that A_g and E_g phonon modes are identified as the primary drivers of this anisotropy due to enhanced momentum randomization along the z direction. These results provide a comprehensive understanding of high-field electron transport in α-Ga₂O₃, offering valuable insights for optimizing high-power electronic devices.

Conclusion

      In summary, we have revealed the microscopic mechanism behind the high-field transport anisotropy in α-Ga₂O₃. Quantitative analysis confirms that the strong momentum relaxation caused by A_g and E_g phonons along the z direction is the root cause of velocity sup pression. By explicitly including secondary valleys and monitoring transitions in real-time, we have established the validity of the high- field electron transport model for fields up to 1 MV/cm. Combined with rigorous 200³ mesh convergence tests, this work provides a definitive physical picture of hot-carrier effects in ultra-wide-bandgap semiconductors and offers critical insights for device orientation optimization.

Project Support

      This work was supported by C. K. Tan start-up fund from the Hong Kong University of Science and Technology Guangzhou); Guangzhou Municipal Science and Technology Project (Nos. 2023A03J0003, 2023A03J0013, 2023A04J0310, and 2023A03J0152); Department of Education of Guangdong Province (No. 2024ZDZX1005); State Administration of Foreign Experts Affairs (No. Y20240005); Matching Funding for Selected Talent of National Programs (No. CZ118SC24007); National Major Talent Project (No. CZ118SC25005); Excellent Young Scientists Fund (overseas) (No. RK118QN24006); Materials Characterization and Preparation Facility (MCPF); and Green Materials Laboratory at the Hong Kong University of Science and Technology (Guangzhou).