Abstract
InAs QD lasers grown on GaAs substrates have already been demonstrated to have very low threshold currents and current densities [1-3], but until recently their To’s have not been much higher than that of InP-based lasers. The 1.3-micron QD lasers have also been unable to demonstrate the predicted high modulation bandwidths, and in fact are inferior to planar quantum well lasers in this respect. We believe that the cause, as opposed to a relaxation problem such as a phonon bottleneck, lies in the electronic structure of the InAs QDs that also limits their optical gain. The problem essentially is due to closely spaced hole levels that destroy the otherwise ideal performance expected of QD lasers. In self-assembled InGaAs QDs, the electron energy level spacing is much greater than that of holes, and can be as much as ~80 meV for electrons and only ~10 meV for holes. As a result, at and above room temperature, injected holes are distributed over a number of energy levels, which leads to the decrease in the optical and differential gain. Consequently, the threshold and differential gain become very temperature sensitive, and the modulation bandwidth is lowered.
© 2003 Optical Society of America
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