Abstract
In this study, the optical properties of InAs quantum dots (QDs) were characterized using photoluminescence (PL) measurements. The QDs, capped with GaAs and GaAs1−xSbx (x = 6%) strain-reducing layer (SRL), were grown by Molecular Beam Epitaxy. Temperature-dependent photoluminescence (TDPL) of both ground state (GS) and first excited state (ES) was carried out through the analysis of the PL peak position as well as the integrated PL intensity. The temperature dependence of the integrated PL intensity shows the carrier trapping in the potential barrier at the interface between the capping layer and QDs in both samples at low temperatures for the GS and ES. The Excitation density dependent photoluminescence (EDPL) showed a redshift of the GS and ES PL peak energies with increasing excitation density. We attribute this variation to the bandgap renormalization (BGR) effect. The potential barrier reduction for the GaAsSb-capped QDs increases carrier injection efficiency inside the QDs, giving rise to a larger BGR effect compared to the QDs capped with GaAs. With increasing temperature, BGR redshift varies considerably for the GaAs- capped QDs but less for the Q with GaAsSb SRL. This effect was explained using the population rate of carriers inside the QDs while taking into account the nonradiative recombination process for the two samples. Furthermore, the variation of the integrated intensity with the excitation power density grows superlinearly for the two samples for a temperature range from 10 K to 220 K. This behavior was explained by the random capture of carriers in the dots. The sample with GaAsSb SRL having a smaller potential barrier has reduced superlinear dependence at low temperatures. Losses mechanism has a significant impact on increasing the superlinear dependence at high temperatures. The ES showed a stronger superlinearity compared to the GS. This study helps to understand the optical mechanisms in some devices, such as QD lasers.
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