films*

The wide-bandgap semiconductor Ga₂O₃ is a promising candidate for high-power electronics. Alloying with Al for (Al_xGa_1-x)₂O₃ films enables heterostructures that are essential for device applications. However, the limited thickness of (Al_xGa_1-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].¹ Surface energies and elastic constants are computed for the end compounds—monoclinic Ga₂O₃ and Al₂O₃—and used to interpolate to (Al_xGa_1-x)₂O₃ alloys. The appropriate crack plane for each orientation is determined, and the corresponding critical thicknesses 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. A key conclusion is that the critical thickness is largest for (Al_xGa_1-x)₂O₃ films grown along [100].

1. Sai Mu, Mengen Wang, Hartwin Peelaers, Chris G. Van de Walle, APL Materials 8, 091105 (2020).