Anomalous damping in MQW lasers due to slow inter-well transport

The authors present a model for MQW (multiple quantum well) lasers, using the laser rate equations, which includes transport of carriers between the individual wells of MQW lasers. This model provides the first consistent explanation for the anomalously high damping in MQW lasers. It is found that, while electron and hole transfer times both are of the order of 3 ps for typical InGaAs/InGaAlAs structures, hole transfer is much slower than electron transfer in InGaAs/InGaAsP structures, with the hole transfer time being of the order of 100 ps. Since the stimulated recombination times are of the order of 100 ps, this means that one may expect an inhomogeneous hole distribution for the latter case, whereas the carrier distribution is homogeneous for the former case. The effective differential gain derived from the resonance frequency vs. power is found to be almost equal for the two types of lasers. There is a significantly higher damping for the InGaAs/InGaAsP laser, which can be described by an effective gain compression factor almost four times higher than for InGaAs/InGaAlAs.