Optical properties in type-II GaAs/AlAs superlattices

An extensive study of time-resolved photoluminescence is made at low temperature in short -period GaAs-AlAs Superlattices of Type II. We have 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 as a function of AlAs and GaAs layer thicknesses. Excitons localised by interface roughness are found to decay through radiative processes at low temperature.