Band Offsets at β/γ-$\mathrm{Ga}_{2}\mathrm{O}_{3}$ Interface

Abstract: Ultrawide bandgap semiconductor gallium oxide (Ga2O3) and its polymorphs have recently attracted increasing attention across physics, materials science, and electronics communities. In particular, the self-organized formation of the beta/gamma-Ga2O3 double polymorph structures was demonstrated recently [A. Azarov et al., Nat. Commun. 14, 4855 (2023)], paving the way for prospective applications of such structures in electronics. Consequently, determining the conduction band offset in such structures is crucial since it dictates the behavior of conduction electrons at the interface and, consequently, the potential functionality of such interfaces. Thus, in this work, we calculate the band offsets at the beta/gamma-Ga2O3 interface using density functional theory in correlation with the data provided by the experimental atomistic interface analysis. Specifically, to unravel the strain state of the beta/gamma-Ga2O3 interface, nanoscale strain maps were recorded using high-resolution transmission electron microscopy. In its turn, theoretically, lineup potential and vacuum alignment methods were used to analyze the band offsets, with and without strain, at the beta/gamma-Ga2O3 interface. Altogether, the collected results suggest that the band offsets between the beta and gamma phases are likely not exceeding a few hundred meV, remaining highly sensitive to the strain state at the interface. At this end, we conclude that even though the formation of a two-dimensional electron gas (2DEG) at the beta/gamma interface is theoretically possible, the gradual strain relaxation--if it occurs as a function of the distance from the interface--poses a significant challenge, as it may shift the 2DEG localization or even reduce the overall probability of its formation.