THEORY OF ABSORPTION-SPECTRA FOR ABOVE-BARRIER EXCITONS IN SEMICONDUCTOR SUPERLATTICES

We present theoretical studies of absorption spectra associated with a bove-barrier.excitons in semiconductor superlattices. Using a k-space sampling technique combined with the recursion method, we obtain absor ption spectra of both type-I and type-II superlattices. Excitonic effe ct, valence-band mixing, and Fano resonances due to the interaction of discrete exciton states with continua are all properly taken into acc ount. We find hat electrons and holes localized in the barrier region of a superlattice do form quasibound exciton states that appear as pro minent features in the absorption spectra. Our calculation offers a di rect comparison between theory and experiment.