Tailoring light holes in β − Ga 2 O 3 via anion-anion antibonding coupling

A significant limitation of wide-band-gap materials is their low hole mobility related to localized holes with heavy effective masses $({m}_{h}^{*})$. We identify in low-symmetric wide-band-gap compounds an anion-anion antibonding coupling (AAAC) effect as the intrinsic factor behind hole localization, which explains the extremely heavy ${m}_{h}^{*}$ and self-trapped hole (STH) formation observed in gallium oxide $(\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3})$. We propose a design principle for achieving light holes by manipulating AAAC, demonstrating that specific strain conditions can reduce ${m}_{h}^{*}$ in $\ensuremath{\beta}\text{\ensuremath{-}}{\mathrm{Ga}}_{2}{\mathrm{O}}_{3}$ along ${c}^{*}$ from 4.77 ${m}_{0}$ to 0.38 ${m}_{0}$, making it comparable to the electron mass $(0.28 {m}_{0})$ while also slightly suppressing the formation of self-trapped holes, evidenced by the reduction in the formation energy of hole polarons from \ensuremath{-}0.57 to \ensuremath{-}0.45 eV under tensile strain. The light holes show significant anisotropy, potentially enabling two-dimensional transport in bulk material. This study provides a fundamental understanding of hole mass enhancement and STH formation in novel wide-band-gap materials and suggests new pathways for engineering hole mobilities.