Density-dependent transition from electron to ambipolar vertical transport in short-period GaAs-AlGaAs superlattices

Using time-resolved photoluminescence the authors have studied vertical transport in a series of superlattices with a large included 1 mu m away from the sample surface. With a streak camera, photoluminescence (PL) decays for excitation densities as low as a few 1013 cm-3 photocarriers per pulse can be recorded. At such low densities, the electrons are the minority carriers in residual p-type MBE materials. They can move without being slowed down by the holes. By varying the excitation density one is able to observe the transition from an electron transport regime to an ambipolar one. The use of a one-dimensional diffusion model for the photocreated carriers and the excitons enables one to obtain the diffusion coefficients of electrons, holes and excitons in these structures at different temperatures.