Optical nonlinearities and lasing in II–VI multiple quantum wells

We investigated optical nonlinearities and stimulated emission in Zn 1−xCdxSe/ZnSe multiple quantum well structures by using pump and probe transmission and high intensity photoluminescence (PL) measurements with or without magnetic field. We found that the origin of stimulated emission in the investigated samples depends on the exciton stability which can be increased by localization due to compositional and structural parameters. Exciton localization is directly demonstrated by time resolved PL measurements. A complex dynamics between excitons and free-carriers governs the physical mechanisms responsible for stimulated emission. This has been elucidated in detail by a many body theoretical model which has been used to analyze the experimental data based on an equilibrium phase diagram between excitons and free-carriers. Evidence of biexciton recombination is also given, and the stability of such excitonic molecules is investigated in modulation-doped quantum well structures.