Multiple-quantum-well structures show thermally activated quenching of the photoluminescence.There are also small changes in photoluminescence intensity as carriers emitted from one well are retrapped in another. We present a coupled-well rate-equation theory which successfully models these changes in intensity in In~Ga&~As/GaAs and In~Ga&~As/GaAs/Al"Ga& "As structures. In both structures, the dominant nonradiative carrier loss from the wells is due to thermal excitation to the barriers; retrapping in the wells can be observed and is included in the model. In contrast, in In~Ga&~As/Al Ga, "As quantum wells, a defect-related nonradiative mechanism dominates even with an Al content in the Al"Gal As of only 5%.
We have studied the intrinsic factors which determine the threshold current and its temperature dependence in 160-Å-wide In0.2Ga0.8As single well quantum lasers with GaAs barriers, grown by molecular beam epitaxy on GaAs substrates. By measuring the relative temperature dependence of the spontaneous emission intensity at threshold we show that radiative transitions between higher order (n=2,3) electron and heavy hole subbands make a significant contribution to the threshold current and its temperature sensitivity, even in devices where the laser transitions are between n=1 subbands. These higher transitions will also influence the dependence of threshold current and its temperature sensitivity on well width.
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