(Zn,Cd)Se/ZnSe quantum-well lasers: Excitonic gain in an inhomogeneously broadened quasi-two-dimensional system

Optical properties of a strongly excitonic quasi-two-dimensional system in a wide-band-gap II-VI semiconductor heterostructure are investigated in terms of the relationship between absorption and stimulated emission. In particular, the optical gain in (Zn,Cd)Se/ZnSe quantum-well lasers is demonstrated to be of excitonic nature over a wide range of temperatures, and to occur at electron-hole pair densities below the exciton-electron hole plasma transition. Both steady-state and transient (picosecond and femtosecond) spectroscopic techniques have been applied to detail exciton kinetics within the n=1 heavy-hole exciton resonance. A phenomenological model of optical gain is proposed, originating from an inhomogeneously broadened exciton resonance and including the effects of exciton-phonon interaction.