Epitaxial strain effect on the band gap of a Ga2O3 wide bandgap material

The effects of a uniform and biaxial strain on the electronic structure of wide-bandgap orthorhombic Ga2O3 are studied using density-functional theory with the generalized gradient approximation (GGA) and the meta-GGA. Under uniform strain, as the strain increases, the lattice constants of the system decrease and the bandgap increases. However, under epitaxial strain, the bandgap increases with increasing compressive strain up to a certain level, and further increasing the compressive strain decreases the bandgap. This phenomenon is closely related to Poisson's ratio and increases of the lattice constant along the c-axis, which is not constrained by the epitaxial strain.