Excited states ofDXinGa1−xAlxAs

The photoexcited neutral states of the Sn donors in ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Al}}_{\mathit{x}}$As alloys are studied both experimentally and theoretically. Two types of donor states are evidenced: a deep strongly localized one, ${\mathit{D}}^0$, as well as a delocalized effective-mass state ${\mathit{d}}^0$. Both belong to the principal donor ${\mathrm{Sn}}_{\mathrm{Ga}}$, as confirmed by EPR measurements on ${}_{}{}^{119}{}_{}{}^{}\mathrm{enriched}$ samples. The ${\mathit{D}}^0$ state is consistently modeled as the ${\mathit{A}}_1$(ab) antibonding donor state. Theory predicts the coexistence of both states ${\mathit{D}}^0$,${\mathit{d}}^0$ in an intermediate alloy-composition range. This level scheme also explains the results of the Si and Te donor reported previously.