NONLINEAR GAIN COEFFICIENTS IN SEMICONDUCTOR QUANTUM-WELL LASERS - EFFECTS OF CARRIER DIFFUSION, CAPTURE, AND ESCAPE

Effective nonlinear gain coefficients due to the effects of carrier di ffusion, capture, and escape are derived from the carrier transport eq uations, The quantum capture and escape processes between the confined states and the unconfined states are calculated from first principles by evaluating the carrier-polar longitudinal optical phonon interacti ons, The de and ac capture times and escape times are derived from eva luating the net capture current of carriers, The differences in captur e and escape times between de and ac operating conditions are numerica lly investigated, We find that both de and ac escape times are strongl y dependent on the quantum well structure, This differs from the de an d ac capture times that are not sensitive to the quantum well structur e. We also find that the de escape time predicted by the classical the rmionic emission theory will no longer be valid for narrow or shallow quantum wells, We show that both de and ac capture and escape time rat ios mill increase as the carrier temperature and the carrier density i n the quantum wed increase, Therefore, we suggest that the possible ca use of the resonant frequency degradation and dramatic increase in the damping rate results from the increase of the ac capture to escape ti me ratio by the effects of carrier heating, Two theoretical models (2N and 3N models) were used to study the effects of carrier diffusion-ca pture-escape on the modulation response of quantum-well lasers and a d istributed model of carrier transport in quantum-well lasers is propos ed, Their implications in designing high-speed quantum-well lasers are discussed.