THE THEORY OF STRAINED-LAYER QUANTUM-WELL LASERS WITH BANDGAP RENORMALIZATION

A theoretical model for the strained-layer quantum-well laser is presented taking into account the valence-band mixing and the bandgap renormalization. Our theoretical approach for the electronic properties is based on the Luttinger-Kohn Hamiltonian, including the strains and the carrier-induced bandgap shifts using the Hartree-Fock approximation. The effects of the biaxial compressive and tensile strains on the gain, the output characteristics, the bandgap renormalization, and the modulation response of strained-layer quantum-well lasers are studied. We present new results incorporating the many-body effects in the form of the bandgap renormalization with the valence-band mixing and the multisubband effects. It is found that the bandgap renormalization depends strongly on the nature of strain applied to the quantum well. The differential gain that determines the upper frequency limit of the direct current modulation is calculated from the total derivative of the equigain surface with respect to the carrier- and the photon-densities near the threshold condition. Our approach to the differential gain yields reasonable agreement between theory and experiment for the 3-dB modulation bandwidth. Both InGaAs-AlGaAs and InGaAs-InP strained quantum-well systems are considered.