Optical gain of a quantum-well laser with non-Markovian relaxation and many-body effects

In this article, a theoretical description of the optical gain of a quantum-well laser is developed taking into account non-Markovian relaxation and many-body effects. Single-particle energies are calculated using the multiband effective mass theory, and the valence-band mixing including the spin-orbit (SO) split-off band coupling is considered in the formulation. The Coulomb enhancement and the band-gap renormalization are also considered within the Hartree-Fock approximation. The gain spectra calculated with the Lorentzian line shape function show two anomalous phenomena: unnatural absorption region below the band-gap energy and mismatch of the transparency point in the gain spectra with the Fermi-level separation, the latter suggesting that the carriers and the photons are not in thermal (or quasi-) equilibrium. It is shown that the non-Markovian gain model with many-body effects removes the two anomalies associated with the Lorentzian line shape function. It is also found that the optical gain spectra depend strongly on the correlation time of the system which can be determined by the intraband frequency fluctuations.