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

We have measured the absolute absorption coefficient of optical transi tions in type-II short period GaAs/AlAs superlattices, on a broad spec tral range, at low temperature. The transmission experiments have been performed in a waveguiding configuration. Photoluminescence excitatio n 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 ex citon resonance frequency are presented, taking explicitely into accou nt the GAMMA-X mixing of electronic states at heteroboundaries. From c omparison between the experimental and theoretical values of the absor ption coefficients, we have deduced a value of the GAMMA-X coupling co efficient for the studied superlattices.