Four-dimensional picosecond exciton capture at the interface in symmetric and asymmetric quantum wells

Abstract

Exciton dynamics at the interface have been investigated in symmetric and asymmetric GaAs quantum wells by means of four-dimensional picosecond time-resolved photoluminescence spectroscopy at different temperatures. The spectral and temporal resolutions of the system are 2.5 nm and 9.7 ps, respectively. Twenty-five periods of Al0.3Ga0.7As-GaAs-Al0.3Ga0.7As symmetric quantum wells (SQWs) and Al0.3Ga0.7As-GaAs-AlAs asymmetric quantum wells (AQWs) grown on GaAs substrates by a molecular-beam epitaxy Method were investigated. The thicknesses of the layers are 200, 50, and 200 A, respectively. The temporal profile of photoluminescence for SQWs is singleexponential, with a 260 ps decay time, whereas a two-exponential decay profile is observed for AQWs, which have a fast decay of 90 ps and slow decay of 950 ps. The fastdecay component arises from excitonic recombination in the quantum well, which is dominated by nonradiative capture at the interface between GaAs and AlAs and its alloys. These results suggest that the roughness of the interface between GaAs and AlAs has been found to produce more nonradiative pathways than that between GaAs and AlGaAs. It is also found that the bound states with a binding energy of 3.5 meV are responsible for the exciton capture process at the interface.