RECOMBINATION PROCESSES IN SHORT-PERIOD GAAS-ALAS SUPERLATTICES OF TYPE-II

An extensive study of time-resolved photoluminescence is made in the temperature range 1.8 to 50 K on nine samples of type-11 GaAs-AlAs (001) superlattices. In previous publications, the region is identified where the states derived from X(z). valleys are lower than those derived from X(xy) valleys, in agreement with a simple model involving the competition between X-type valley anisotropy and X valleys splitting caused by the small lattice mismatch between AlAs and GaAs. An analysis is given of the luminescence processes and of their evolution with temperature, as a function of AlAs and GaAs layer thicknesses. Excitons localized by interface roughness are found to decay through radiative processes at low temperature. A model of thermal excitation from the tail of localized exciton states is introduced, which helps to identify the pertinent parameters of temperature behaviour in these samples.