Periodic behavior of the exciton oscillator strength with AlAs thickness in type II GaAs/AlAs heterostructures

For a single GaAs/AlAs/GaAs type II pseudodirect double quantum well, as we ll as for superlattices it was predicted that the oscillator strength of th e lowest optical transition has a periodic dependence on the number of AlAs monolayers. The oscillator strength depends on the coupling between the Ga mma and X electron states. We use samples containing a single GaAs/AlAs/GaA s double quantum well with thickness gradient to show experimental evidence of this effect. The results concerning the Gamma -X coupling are obtained from the study of the ratio of photoluminescence intensities of the zero-ph onon line and the phonon replica and from their time decay. They show the m onolayer dependence of the Gamma -X mixing potential. We extend the model d escribing the Gamma -X coupling for ideal interfaces in the frame of the en velope approximation to the case of non-abrupt interfaces and exciton local ization. The amplitude of variation of the radiative recombination time due to the Gamma -X mixing is well reproduced within this model.