GAMMA-X MIXING IN TYPE-II GAAS/ALAS SHORT-PERIOD SUPERLATTICES

We have measured the absolute absorption coefficient of optical transitions in type-II short period GaAs/AlAs superlattices, on a broad spectral range, at low temperature. The transmission experiments have been performed in a waveguiding configuration. Photoluminescence excitation experiments show as well the characteristics of the pseudodirect HH1-X(z) excitonic transition. Theoretical calculations of the effective dielectric tensor and absorption coefficient in the vicinity of the exciton resonance frequency are presented, taking explicitely into account the GAMMA-X mixing of electronic states at heteroboundaries. From comparison between the experimental and theoretical values of the absorption coefficients, we have deduced a value of the GAMMA-X coupling coefficient for the studied superlattices.