Computational design of optimal heterostructures for β-Ga_2O_3

Ga_2O_3 is a wide-bandgap material of interest for a wide variety of devices, many of these requiring heterostructures, for instance to achieve carrier confinement. A common method to create such heterostructures is to alloy with In_2O_3 or Al_2O_3. However, the lattice constants of these materials are significantly different from those of Ga_2O_3, leading to large amounts of strain in the resulting heterostructure. If the thickness of the heterostructure is increased, this can lead to cracking. By considering alloys of In_2O_3 and Al_2O_3, the lattice constants can be tailored to those of Ga_2O_3, while still keeping a sizable conduction-band offset. We use density functional theory with hybrid functionals to investigate the structural and electronic properties of In_2O_3 and Al_2O_3 alloys in the bixbyite, corundum, and monoclinic structures. We find that the lattice constants increase with In incorporation. Bandgaps decrease nonlinearly with increasing In concentration. We find the (In_ 0.25Al_ 0.75)_ 2O_ 3 monoclinic structure to be of particular interest, as it closely matches the Ga_2O_3 lattice constants while providing an indirect/direct bandgap of 5.94/5.70 eV and a conduction-band offset of 1 eV compared to Ga_2O_3.