ANALYSIS OF DIFFERENTIAL GAIN IN INGAAS INGAASP COMPRESSIVE AND TENSILE STRAINED QUANTUM-WELL LASERS AND ITS APPLICATION FOR ESTIMATION OF HIGH-SPEED MODULATION LIMIT

A simplified model, which furnishes an intutitive insight for the change in quantum-well (QW) laser gain, due to QW strain and quantum confinement, is presented. Differential gain, for InGaAs-InGaAsP compressive and tensile strained multi-quantum-well (MQW) lasers, is studied using the model. The comparsion, between the calculated and experimental results for lattice-matched and compressive strained MQW lasers, shows that this model also gives quantitatively reasonable results. It is found that the valence-band harrier height strongly affects the differential gain, especially, for compressive strained MQW lasers. The tensile strained MQW lasers are found to have quite high differential gain, due to large dipole matrix element for the electron-light hole transition, in spite of the large valence-band state density. Furthermore, a great improvement in the differential gain is expected by modulation p doping in the tensile strained MQW lasers. Finally, the ultimate modulation bandwidth for such lasers is studied, using the above results.