Localized and extended states inGaAsAlxGa1−xAssuperlattices probed by resonant optical excitation

Using the excitation energy dependence of luminescence spectra of purposely disordered short-period $\frac{\mathrm{GaAs}}{{\mathrm{Al}}_x{\mathrm{Ga}}_{1-x}\mathrm{As}}$ superlattices, we demonstrate the existence of localized states in the miniband structure. We present for the first time a clear indication of the existence of different energy regions corresponding to spatially confined (localized) and extended states. We show the saturation of the localized states by increasing the intensity of the exciting light.