GAMMA-X MIXING EFFECTS ON PHOTOLUMINESCENCE INTENSITY IN GAAS/ALAS TYPE-II SUPERLATTICES

We have investigated GAMMA-X mixing effects on the no-phonon assisted (pseudodirect) transition between the n=1 X(z)-electron and the n=1 GAMMA-heavy-hole states in [001]-(GaAs)m/(AlAs)m type-II superlattices (m=8-13 monolayers) by using photoluminescence (PL) and PL-excitation (PLE) spectroscopies. We have estimated the relative oscillator strength of the pseudodirect transition to the direct transition between the n=1 GAMMA-electron and GAMMA-heavy-hole states from the relative PLE intensity and the extrapolated relative PL intensity at infinite temperature. It is found that the relative oscillator strength is almost constant value of approximately 3x10(-4) for each sample. According to a first-order perturbation theory, we evaluate a GAMMA-X mixing factor as a function of the layer thickness from the relative oscillator strength, and show that the mixing factor, which gradually increases from approximately 0.8 to approximately 1.9 meV with decreasing the layer thickness, is mainly determined by the envelope-function overlap of the GAMMA and X(z) electrons.