Orthorhombic alloys of Ga2O3 and Al2O3

Abstract

Ga 2 O 3 has attracted significant attention as a wide-bandgap material for electronic applications. The orthorhombic κ phase is of interest due to its large predicted spontaneous electrical polarization. Here, we use density functional theory and hybrid functionals to investigate how alloying Ga2O3 with Al2O3 can be used to modify lattice constants, bandgaps, and conduction-band offsets. We find that increasing the Al content decreases lattice constants linearly, but that the increase in bandgaps and conduction-band offsets is non-linear, with a bowing of 1.41 eV. Structurally, there is a strong energetic preference of Al atoms to occupy octahedrally coordinated sites, and of Ga atoms to occupy tetrahedral sites. Ga will also occupy pentahedral sites, but at a small energy cost. The formation enthalpy of alloys is smaller than that of the pure materials, with ordered alloys with 50% Al having especially low formation enthalpies. These quantitative results can be used to guide experimental device design.