Excitonic gain and laser emission in ZnSe-based quantum wells.

We show spectroscopically that the origin of optical gain and laser emission in (Zn,Cd)Se/ZnSe quantum wells at blue-green wavelengths is of excitonic nature. This circumstance derives from the large enhancement in the exciton binding and its oscillator strength which occurs in the quasi-2D case, so that an exciton gas is stable against ionization by optical phonons up to room temperature and that gain in the context of partial phase-space filling can develop at pair densities below the onset to an electron-hole plasma