TENSILE STRAIN AND THRESHOLD CURRENTS IN GAASP-ALGAAS SINGLE-QUANTUM-WELL LASERS

The effects of tensile strain on threshold current in GaAsP-AlGaAs qua ntum well lasers are studied theoretically and experimentally. A compr ehensive model for the light-current characteristics of separate-confi nement strained-layer lasers, which is based on a six-band Luttinger-K ohn valence dispersion model, is first developed, Theoretical and expe rimental results for broad stripe single-well laser diodes with a cons tant well width of 115 Angstrom are then presented, Experimentally obs erved variations in threshold currents and TE/TM polarization switchin g are accurately described by the model for phosphorus compositions in the quantum-wed ranging from 0 to 0.30 and cavity lengths ranging fro m 300 to 1500 mu m, Constant-gain contours generated from the theoreti cal model are shown to provide a simple and powerful guide to various regimes of operation, Our studies show that tensile strain-related eff ects lower threshold currents in GaAsP-AlGaAs only in the high gain (s hort cavity) regime, and suggest more generally that the threshold adv antages offered by tensile strain are conditional.