Studies of donor states in Si-doped Al_xGa_1-xAs using optically detected magnetic resonance with uniaxial stress

Optically detected magnetic resonance experiments with uniaxial stress along the (110) and (100) directions have been performed on Si-doped epitaxial layers of AlAs and Al0.4Ga0.6As grown on (001) GaAs substrates. These studies enable the symmetry of the donor wavefunction to be probed in detail. The results obtained with T mod mod (100) confirm the independent valley description for Si donor states in AlAs. The lack of a response to uniaxial stress along (110) provides evidence against the contribution of donor states derived from the L-point conduction band minima and against a purely spin-valley coupled state at x=0.4.