Study of type-I and type-II strained quantum-well lasers

Semiconductor lasers with three types of quantum wells (QWs) (type-I, staggered type-II, and broken-gap type-II QWs) are studied. For a type-I QW structure, the 1.55-pm InGaAsP and InGaAlAs QW lasers are investigated both in the steady-state and high-speed modulation schemes. We show excellent agreement of our experimental data with the results of our theoretical gain model with many-body effects. The temperature-dependent characteristics of both material systems are compared. The InGaAsP laser has a better performance in terms of high-modulation bandwidth. But this advantage, is offset by severe Auger recombination rate. A new technique based on injection locking for measuring the linewidth enhancement factor is developed, and we extract the linewidth enhancement factor for the above three lasers. They are also calculated using the same parameters extracted from the gain spectra and agree with the experimental results very well. For a staggered type-II QW structure, the GaAs _1−xSb_x/GaAs QW lasers at 1.3 μm for VCSELs are studied. We present a comprehensive model for determining the band-edge profile of the GaAs_1−xSb _x QW systems by fitting a large set of experimental data. Then a self-consistent model for the band structure with carrier population is used in the calculation of the optical gain. We find that a sufficient gain can be achieved for lasing action with these type-II QW lasers due to the free-carrier screening effect. For a broken-gap type-II QW structure, the interband Sb-based quantum-cascade lasers at mid-IR range are studied. We use a block-diagonalized 8 x 8 Hamiltonian based on the k·p method, taking account of the coupling between the conduction and valence bands, and apply a self-consistent treatment to obtain the band structure. Numerical results are presented and compared with experimental data. It is shown that the self-consistent model is necessary to give a better agreement with the experimental results.