NOVEL DESIGN SCHEME FOR HIGH-SPEED MQW LASERS WITH ENHANCED DIFFERENTIAL GAIN AND REDUCED CARRIER TRANSPORT EFFECT

We present a theoretical analysis exploring the optimum design of high -speed multiple-quantum-well (MQW) lasers for 1.55-mu m operation. Var ious combinations of well and barrier materials are examined for latti ce-matched, strained-layered (SL), and strain-compensated (SC) MQW las ers with InGaAsP and InGaAlAs barriers. The gain characteristics are i nvestigated for these MQW lasers with various barrier bandgap waveleng ths and are used to evaluate the modulation characteristics based on t he carrier dynamics model which includes a set of Poisson, continuity, and rate equations, The importance of band engineering aimed at simul taneously reducing the carrier transport effect and enhancing the diff erential gain is described. It is shown that SC-MQW lasers with InGaAl As barriers have an advantage in reducing the density of states in the valence hand by reducing the overlap integral between the heavy- and light-hole wave functions, which effect has previously been discarded as a minor correction in designing conventional InGaAsP-based MQW lase rs. Furthermore, the hole transport rate across the barriers can be dr astically reduced in SC-MQW lasers clue to the reduced effective barri er height for the holes. Based on this novel design scheme, a 3-dB ban dwidth approaching 70 GHz is expected for 20-well SC-MQW lasers with I nGaAlAs barriers as a result of both the large differential gain and r educed transport effect.