Valence-band-mixing effects on the optical gain of GaAs/AlxGa1-xAs graded single quantum wells

Full text: In the last few years the semiconductor lasers have been attractive for research because they are both physically very interesting and technologically important. This is especially true for quantum well lasers since, with the current technology of quantum wells, it is possible to control the range, depth, and arrangement of quantum mechanical potential wells, which can be useful to make very good lasers. In the last decade the importance of the quantum well laser has steadily grown until today, where it is preferred for most semiconductor laser applications. This growing popularity is because, in almost every aspect, the quantum well laser is somewhat better than the conventional one with bulk active layers. In this work, we have calculated the optical gain spectra in the unstrained graded GaAs/Al0.2Ga0.8As single quantum well laser as a function of the energy of the radiation and the interface width. The calculation of the electronic structure was done using the parabolic band model. The calculation of the valence band structure was done taking into account the effects of sub-band mixing between the heavy and light holes, as well as by using an effective Hamiltonian approach based on the k-vector · p-vector Luttinger-Kohn method. The optical gain was calculated using the density matrix approach, considering all sub-band transitions in the quantum well. We consider both the transversal electrical and the transversal magnetic light polarization. Our results show that the peak gain is sensitive to the width and the graded profile of the interfaces, and the gain spectrum is blue-shifted as a function of the interface width. (author)