Role of Interface Imperfections on Intervalley Coupling in GaAs/AlAs Superlattices

We present a systematic study of the intervalley couplings $\Gamma -X_{1z}$, $\Gamma -X_{3z}$, $X_{1x}-X_{1y}$, and $X_{3x}-X_{3y}$ in GaAs/AlAs superlattices using the tight-binding formalism. We find that a $\Gamma -X_{1z}$ coupling is obtained by a modification of the first-neighbor hopping at the interface. All four couplings scale inversely with the superlattice period, in agreement with experiment. We calculate the effect of interface alloying on the couplings, considering both even and odd monolayer numbers for GaAs and AlAs. Remarkably, all intervalley couplings are independent of the degree of interface alloying when averaged over the four possible even/odd configurations.