Gain and Threshold of Quantum Dot Lasers: Theory and Comparison to Experiments

A theory for gain and threshold of quantum dot lasers operating with inhomogeneously broadened dot ensembles is developed. Separate vs. simultaneous electron and hole capture and thermal vs. non-thermal carrier distributions and vertically coupled stacks are considered. In realistic lasers thermally distributed carriers allow lower threshold currents than non-thermal ensembles. Stacked quantum dots provide larger maximum gain but have a priori a higher threshold. However, vertical coupling leads to a redistribution of the carrier population and subsequently to similarly low thresholds as for lasers operating with single sheets of dots. Theoretical predictions are compared to experiments on quantum dot lasers operating on self-organized InAs/GaAs quantum dots.