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.
Optical properties of blue AlInGaN/InGaN quantum well (QW) structures with a quaternary AlInGaN well layer were investigated by using the non-Markovian gain model with many-body effects. The band-gap expression of the AlInGaN materials was determined through a comparison with experimental results. We found that the emission peak can be enhanced by using quaternary AlInGaN well and is sensitive on In composition in the InGaN barrier. For example, the spontaneous emission coefficient for Al0.08In0.22Ga0.67 N/InxGa1−xN QW structures shows a maximum at In composition of 0.13 in the barrier and gradually decreases with increasing In composition. This is attributed to the fact that the quasi-Fermi-level separation linearly decreases with increasing In composition in the barrier due to the decrease in the conduction and valence band offsets. The AlInGaN/InGaN system with zero internal field is found to have smaller emission peak than the AlInGaN/InGaN system with nonzero internal field due to smaller band offsets.
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