ANALYSIS OF DIFFERENTIAL GAIN IN GAAS/ALGAAS QUANTUM-WELL LASERS

The differential gain of a quantum-well laser is studied theoretically with use of both a parabolic band model and a valence-band-mixing model. In the valence-band-mixing model, the gain profile is derived from the multiband effective mass theory (k.p method) as well as the density matrix formalism. The peak gain including the band-mixing effect is significantly reduced to 1.5-2 times when compared to the conventional parabolic band model. There is still a larger differential gain using the parabolic band model than using the band-mixing model. The magnitudes of differential gains for these two models give the order of 10(-16)-10(-15) cm2, which is in agreement with the experimental results. Besides, the quantum-well thickness also influences the differential gain, which is enhanced by a thinner quantum-well structure.