Direct evidence of the indirect energy gap in InAlAs/AlAsSb multiple quantum wells by time-resolved photoluminescence

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Abstract
Time-resolved photoluminescence spectroscopy has been applied to determine the nature of the energy gap of InAlAs/AlAsSb multiple quantum well structures. While the InAlAs buffer layer exhibits a decay time of the order of 1 ns, which is typical for direct gap semiconductors, the decay time of the InAlAs/AlAsSb multiple quantum well structures is prolonged by more than two orders of magnitude. This observation is direct evidence for the presence of an indirect energy gap. The decay time increases with increasing InAlAs layer thickness indicating the decreasing overlap of electron and hole wave functions.