Microscopic theory of gain, absorption, and refractive index insemiconductor laser materials-influence of conduction-bandnonparabolicity and Coulomb-induced intersubband coupling

摘要

The influence of the conduction-band nonparabolicity and Coulombncoupling between different electronic subbands and different holensubbands on gain, absorption, and refractive index in semiconductornheterostructures is investigated. We implement these features into anfully microscopic approach. At low carrier densities, thennonparabolicity leads to a steeper increase of the absorption fornincreasing transition energy. In this regime, the Coulomb subbandncoupling allows for a shift of oscillator strength to energeticallynlower transitions. In the gain regime, the conduction-bandnnonparabolicity is shown to reduce the gain width for a given carrierndensity and to strongly modify the corresponding refractive index. ThenCoulomb coupling is especially important to determine the correctnenergetic position and density dependence of the gain maximum. Innaddition, it leads to a steeper transition from the gain to thenabsorptive region