Synergistic effects of pressure and hole doping on polymorphism of Ga2O3

Control of polymorphism in Ga₂O₃ poses a significant challenge. In this study, we investigate the phase stability and transitions of {α}-, {β}-, and {κ}-Ga₂O₃ structures using first-principles calculations. Our analysis of the pressure and energy relationship of Ga₂O₃ polymorphs demonstrates that external pressure can induce the transition from the ground-state monoclinic {β} to the corundum {α} phase, but not to the orthorhombic {κ} phases because of the small volumetric changes and relatively large energy differences. However, taking {κ}-Ga₂O₃ as an example, we propose that introducing holes (e.g., substituting Ga with a valence II ion) can stabilize the metastable phases in combination with pressure because the valence bands of the {κ} phase are higher than those in the {α} and {β} phases. These findings not only rationalize the absence of direct observation of the {β}{→}{κ} transitions with conventional external pressure, but also offer insights into the underlying physical mechanism behind the experimentally observed ion irradiation-induced transitions to metastable phases in Ga₂O₃.