Momentum-dependent CPA approach to disorder-induced intervalley scattering in AlxGa1-xAs

The alloy disorder scattering potential can introduce large k-vector scattering transitions, which are responsible for intervalley scattering. Disorder-induced scattering in AlxGa1-xAs is investigated in reciprocal-lattice space by calculating the (momentum) wave-vector components of the self-energy correction to the virtual-crystal model, using the coherent-potential approximation. The imaginary part of the coherent potential (the self-energy) is responsible for disorder-induced energy-level broadenings as a result of the scattering. The calculated disorder-induced intervalley scattering potential for -X transitions is found to be near the observed experimental value. The results for the disorder-induced L-X intervalley scattering potential are incorporated into an ensemble Monte Carlo simulation of a time-resolved optical pump-probe experiment in Al0.6Ga0.4As. It is found that disorder-induced L-X intervalley scattering lifetimes are 35 times larger than the phonon-induced intervalley scattering lifetimes.