Periodic and purposely disordered superlattices: The effect of continuous and discrete disorder distribution

Selective-excitation photoluminescence measurements were performed on purposely disordered superlattices to study the energy dependence of the motion of resonantly photocreated excitons in disordered superlattices. The disorder was introduced as a random succession of different well widths distributed according to a Gaussian function. We compare the continuous and the discrete Gaussian distributions of the disorder. In the latter case, we report the existence of different energy regions in the superlattice bands, corresponding to extended and spatially confined (localized) states. A calculation of the superlattice miniband spectrum and of the localization lengths for the different energy states suggests that the coupling between similar wells, although on different spatial regions, allows excitonic diffusion for some energies in the discrete Gaussian-disordered superlattice. According to calculations, a continuous Gaussian distribution yields only localized states.