Computational Design of Optimal Heterostructures for Β-Ga_2o_3

Ga_2O_3 is a wide-bandgap material of interest for a wide variety ofdevices, many of these requiring heterostructures, for instance to achievecarrier confinement. A common method to create such heterostructures is toalloy with In_2O_3 or Al_2O_3. However, the lattice constants of thesematerials are significantly different from those of Ga_2O_3, leading tolarge amounts of strain in the resulting heterostructure. If the thickness ofthe heterostructure is increased, this can lead to cracking. By consideringalloys of In_2O_3 and Al_2O_3, the lattice constants can be tailored tothose of Ga_2O_3, while still keeping a sizable conduction-band offset. Weuse density functional theory with hybrid functionals to investigate thestructural and electronic properties of In_2O_3 and Al_2O_3 alloys inthe bixbyite, corundum, and monoclinic structures. We find that the latticeconstants increase with In incorporation. Bandgaps decrease nonlinearly withincreasing In concentration. We find the (In_ 0.25Al_ 0.75)_2O_ 3 monoclinic structure to be of particular interest, as it closelymatches the Ga_2O_3 lattice constants while providing an indirect/directbandgap of 5.94/5.70 eV and a conduction-band offset of 1 eV compared toGa_2O_3.