INTERFACE INDUCED ANISOTROPIC SPLITTING OF EXCITON-STATES IN GAAS/ALAS SHORT-PERIOD SUPERLATTICES

A lifting of degeneracy of the two radiative heavy exciton states was recently put in evidence in GaAs AlAs short period pseudodirect superlattices. Moreover, it was shown that the two sublevels correspond to excitonic electric dipoles aligned along the 〈110〉 crystallographic directions. The two sublevels can be coherently excited by a picosecond pulse polarized along the [100] or the [010] direction. From the time period of the quantum beats between the two sublevels observed during the decay of photoluminescence, we determine the splitting energy. Taking into account a perturbation Hamiltonian of the appropriate symmetry together with the electron-hole exchange interaction, we calculate the splitting energy and find that it is equal to 4EZ √3Δlh where E is the exchange energy, Δlh the energy separation between light and heavy excitons and Z the amplitude of the perturbation. From the experimental results, Z is found to be the same for all the samples studied with a value of 14.5±1.5 meV. The possible physical origins of the splitting are discussed. © 1992.