Efficient $p$-type doping in wide-band-gap (WBG) oxides is fundamentally hindered by their low-lying and localized valence-band maximum (VBM). One promising approach to overcome this limitation is to elevate the VBM through alloy formation. Although the tuning of electronic structures in semiconductor alloys has been widely explored, the defect behavior in such systems remains poorly understood. Here, using first-principles calculations, we investigate the electronic structure and acceptor behavior of dilute α-$\mathrm{G}{\mathrm{a}}_2{\left({\mathrm{S}}_x{\mathrm{O}}_{1-x}\right)}_3$ anion alloys. We show that S incorporation significantly raises the VBM of $\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$, thereby creating favorable conditions for $p$-type doping. Among eight candidate acceptors, $\mathrm{B}{\mathrm{e}}_{\mathrm{Ga}}, \mathrm{M}{\mathrm{g}}_{\mathrm{Ga}}, \mathrm{C}{\mathrm{a}}_{\mathrm{Ga}}, \mathrm{S}{\mathrm{r}}_{\mathrm{Ga}}, \mathrm{Z}{\mathrm{n}}_{\mathrm{Ga}}$, and $\mathrm{C}{\mathrm{d}}_{\mathrm{Ga}}$ remain deep acceptors in the alloy, whereas the very deep $\mathrm{A}{\mathrm{g}}_{\mathrm{Ga}}$ and, notably, $\mathrm{C}{\mathrm{u}}_{\mathrm{Ga}}$ levels in α-$\mathrm{G}{\mathrm{a}}_2{\mathrm{O}}_3$ become much shallower upon alloying. Charge-density analysis reveals that the former six defects form hole-polaron states strongly coupled to the VBM, while $\mathrm{A}{\mathrm{g}}_{\mathrm{Ga}}$ and $\mathrm{C}{\mathrm{u}}_{\mathrm{Ga}}$ are decoupled from the VBM.

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• Defects
• Doping effects
• Electronic structure
• Phase transitions
• Polarons
• Alloys
• Wide band gap systems
• Density functional theory
• First-principles calculations