Synergistic effects of pressure and hole doping on polymorphism of Ga2O3

Control of polymorphism in ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ poses a significant challenge. In this study, we investigate the phase stability and transitions of \ensuremath{\alpha}-, \ensuremath{\beta}-, and \ensuremath{\kappa}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ structures using first-principles calculations. Our analysis of the pressure and energy relationship of ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ polymorphs demonstrates that external pressure can induce the transition from the ground-state monoclinic \ensuremath{\beta} to the corundum \ensuremath{\alpha} phase, but not to the orthorhombic \ensuremath{\kappa} phases because of the small volumetric changes and relatively large energy differences. However, taking \ensuremath{\kappa}-${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ 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 \ensuremath{\kappa} phase are higher than those in the \ensuremath{\alpha} and \ensuremath{\beta} phases. These findings not only rationalize the absence of direct observation of the \ensuremath{\beta}\ensuremath{\rightarrow}\ensuremath{\kappa} 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 ${\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$.