PHONON-ASSISTED GAMMA-X TRANSFER IN (001)-GROWN GAAS/ALAS SUPERLATTICES

A theory of phonon-assisted intervalley GAMMA-X transfer in periodic heterostructures GaAs/AlAs is developed on the basis of the envelope-function approximation. Matrix elements of intervalley transitions are expressed through the overlap integrals of GAMMA and X envelope functions with use of GAMMA-X intervalley deformation potential constants of bulk GaAs and AlAs. The phonon spectrum of an ideal GaAs/AlAs periodic heterostructure is studied in a microscopic approach, It is shown that phonons responsible for intervalley transitions are GaAs-like and AlAs-like X-point LO phonons, confined within GaAs and AlAs layers, respectively. GAMMA-X transfer times due to phonon-assisted scattering are calculated for the problem of photoexcited-electron relaxation in the type-II GaAs/AlAs superlattices and compared with the transfer times due to the phononless transition mechanism (GAMMA-X mixing). Both phonon-assisted GAMMA-X scattering and GAMMA-x mixing are important for the determination of GAMMA-X transfer times. The calculated values of GAMMA-X transfer times and their dependence on GaAs and AlAs layer thicknesses are in agreement with the experimental data.