Monoclinic β-Ga2O3 and its Al alloy (AlxGa1-x)2O3 are wide-bandgap materials and are of active interest due to their promising applications in power electronics. Several polymorphs (α,β,γ,κ) are known and are being pursued due their potential advantages for applications. A thorough understanding of the stability of the competing phases in Ga2O3 and (AlxGa1-x)2O3 is needed to promote the formation of the desired phase for device applications. We employ density functional theory to investigate the phase stability of Ga2O3 and (AlxGa1-x)2O3 at both zero temperature and finite temperature. We reveal that a unique configurational entropy is present in the γ phase due to cation vacancy disorder, and that it substantially contributes to stabilizing the γ phase in (AlxGa1-x)2O3 at finite temperature.
We have used first-principles calculations, based on advanced hybrid density functional theory, to accurately model diffusion of point defects and impurities in Ga2O3. 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. I will discuss impurities used for donor doping, deep acceptors, as well as unintentional contaminants such as carbon and hydrogen. The results provide important guidance for incorporating Ga2O3 into devices.
The wide-bandgap semiconductor Ga2O3 is a promising candidate for high-power electronics. Alloying with Al for (AlxGa1-x)2O3 films enables heterostructures that are essential for device applications. However, the limited thickness of (AlxGa1-x)2O3 films grown on Ga2O3 substrates is a serious obstacle. Here we employ first-principles calculations to determine the brittle fracture toughness of such films for three growth orientations of the monoclinic structure: [100], [010] and [001]. Surface energies and elastic constants are computed for the end compounds—monoclinic Ga2O3 and Al2O3—and used to interpolate to (AlxGa1-x)2O3 alloys. The appropriate crack plane for each growth orientation is determined, and the corresponding critical thicknesses of (AlxGa1-x)2O3 films are calculated based on Griffith’s theory. Our in-depth analysis of surface energies for both relaxed and unrelaxed surfaces provides important insights into the factors that determine the relative stability of different surfaces. We conclude that the critical thickness is largest for (AlxGa1-x)2O3 films grown along [100].
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