Excitonic and biexcitonic recombination in undoped and modulation-doped ${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Cd}}_{\mathrm{x}}$Se/ZnSe quantum-well structures

Undoped and modulated-doped ${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{Cd}}_{\mathrm{x}}$Se/ZnSe multiple quantum wells have been investigated in order to elucidate the role of biexcitons in the physical mechanism responsible for stimulated emission. Though biexcitons are clearly observed in undoped samples at 10 K, the temperature and density dependence of the intensity of the biexcitonic features clearly shows that in the normal operating conditions of quantum-well lasers biexcitons are not stable. Comparison of the energy of the stimulated emission in undoped versus modulation-doped samples allowed us to attribute the origin of lasing to the recombination of localized excitons.