Symmetry of the Si shallow donor state in AlAs/GaAs and ${\mathrm{Al}}_{\mathrm{x}}$${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As/GaAs heterostructures

Optically detected magnetic resonance experiments performed on Si-doped epitaxial layers of AlAs and ${\mathrm{Al}}_{\mathrm{x}}$ ${\mathrm{Ga}}_{1\mathrm{-}\mathrm{x}}$As with x≥0.4 grown on (001) GaAs substrates reveal the donor state to have the symmetry of the X point in the conduction band. The heteroepitaxial strain raises the $X_z$ valley relative to the $X_x$ and $X_y$ valleys. The donor g values for the AlAs/GaAs heterostructure are as follows: $g_{\perp }$=1.976±0.001 and $g_{\perp }$=1.917±0.001 with respect to the long axis of an ellipsoid. The alloy results suggest the importance of spin-orbit interactions in coupling the valley-degenerate shallow-level states.