Output power of a double tunneling-injection quantum dot laser.

We develop a comprehensive theoretical model for a double tunneling-injection (DTI) quantum dot (QD) laser. Both electrons and holes are injected into QDs by tunneling from two separate quantum wells (QWs). Ideally, out-tunneling of each type of carriers from QDs into the opposite-to-injection-side QW should be completely blocked; as a result, the parasitic electron-hole recombination outside QDs will be suppressed and the light-current characteristic (LCC) of a laser will be strictly linear. To scrutinize the potential of a DTI QD laser for high-power operation and the robustness of an actual device, our model includes out-tunneling leakage of carriers from QDs. We complement our calculations by an analytical model and derive closed-form expressions for the LCC and carrier population across the layered structure. We show that, even in the presence of out-tunneling leakage, the flux of parasitic recombination outside QDs remains restricted with increasing injection current. As a consequence, the LCC exhibits a remarkable feature distinguishing the DTI QD laser from other types of injection lasers--it becomes increasingly linear and the slope efficiency grows closer to unity at high injection currents. The linearity is due to the fact that the current paths connecting the opposite sides of the structure lie entirely within the QDs--in view of the three-dimensional confinement in QDs, the out-tunneling fluxes of carriers from dots are limited.