Effect of Out-Tunneling Leakage and Electron-Hole Asymmetry on Modulation Response of Semiconductor Double Tunneling-Injection Quantum Dot Lasers

In this thesis, our primary objective was to theoretically analyze the real world modulation bandwidth of a DTI QD laser and this was done by analyzing the effect of out-tunneling leakage of carriers from QDs, and by analyzing the effect of electron-hole asymmetry on the device characteristics. We are confronted with the following results:

1. Effect of Out-Tunneling Leakage on Modulation Bandwidth in Double Tunneling Injection Quantum Dot Lasers

To purely focus on this effect, the conditions of instantaneous carrier exchange between the OCL and QW (on each side of the structure) and tunneling injection into QDs are assumed and closed-form analytical expressions for modulation bandwidth are obtained. The relative decrease in modulation bandwidth, due to this effect, in a DTI QD laser (from plots of modulation bandwidth vs j on increasing wout) is then shown to be small, and at ranges of injection currents of operational interest, nearly negligible. Consequently, it is shown that the DTI laser is a robust device in terms of sensitivity to out-tunneling leakage i.e. much effort need not be paid in suppressing this phenomenon.

1. Effect of Electron-Hole Asymmetry on Modulation Bandwidth of Double Tunneling Injection Quantum Dot Lasers

On analyzing the effect of electron-hole asymmetry on the device characteristics of a DTI QD laser, it can be noted (from plots of modulation bandwidth vs injection current) that there is no reduction in the maximum modulation bandwidth i.e. electron-hole asymmetry does not indicate a reduction in the effectiveness of such a DTI design. This is shown to occur as the maximum modulation bandwidth depends on both, the effective differential non-stimulated recombination time as well the photon lifetime in the optical cavity. The photon lifetime being much smaller than the former acts as the dominating factor, and hence we see no appreciable change in the maximum modulation bandwidth.

In the course of this analysis, we also see that the actual condition i.e. that of electron hole asymmetry is closer, among the cases of symmetry, to symmetry assuming hole parameters rather than electron parameters. As such, in cases where electron-hole symmetry must be used (in order to facilitate numerical simplifications), a recommendation of this study is to use hole parameters instead.