Cumulant expansion approach to stimulated emission in semiconductor lasers

We present a simple model of absorption and gain spectra in highly excited semiconductor systems that incorporates interactions between electrons and holes. The scattering of the recombining electron-hole pair by charge fluct uations in the plasma is treated to infinite perturbation order by summing the corresponding cumulant series. We further show that the lowest cumulant in our expansion is simply related to the self-energy operator in the GW a pproximation. Our results therefore predict correctly the energy gap renorm alization and the proper line shape of the emission spectra, including the exponential behavior of the spectral edge in the low-energy limit. Numerica l results obtained within the plasmon pole approximation match experimental data in heterojunction lasers without adjustable parameters. Our procedure is sufficiently accurate and simple that it can be used in practical model s of linear and nonlinear gain.