Tetrahedrally symmetric DX-like states of substitutional donors in GaAs and ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As alloys

The structural and electronic properties of Si, Ge, Sn, S, Se, and Te substitutional donors in GaAs are examined via self-consistent pseudopotential calculations. Two distinct negatively charged DX-like deep donor states are found. The first has a broken-bond atomic configuration while the second arises from a symmetric ‘‘breathing-mode’’ relaxation around the impurity. The energies of the two configurations are especially close for Sn, Se, and Te donors. Experimental data on DX centers in ${\mathrm{Al}}_{\mathit{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$As alloys are analyzed within this model.