Photoluminescence dynamics due to exciton and free carrier transport in GaAs/AlAs superlattices

Photogenerated carrier transfer is investigated in a set of three GaAs/AlAs short-period superlattices (SPSs) with different barrier thicknesses by steady-state and time-resolved photoluminescence (PL) spectroscopy at 15-20 K as a function of excitation power. The tunneling transport of carriers is evaluated by detecting excitonic PL signals from an embedded GaAs single quantum well (SQW) in the middle of the SPS layer. We find that, as the barrier thickness is decreased, the PL intensity ratio of SQW/SPS increases systematically due to enhanced tunneling efficiencies of both electrons and holes. However, the PL intensity ratio significantly increases with decreases in the excitation power by more than two orders of the magnitude. We attribute the enhanced PL intensity of SQW relative to the SPS to the faster transport of electrons that can recombine with residual holes to form excitons in SQW. The PL dynamics of SQW and SPS thus shows unique density-dependent PL intensity and time behaviors due to variations in relative amounts of excitons and free carriers to be transported into the SQW layer. (C) 2009 Elsevier B.V. All rights reserved.