Physics Of Gain And Stimulated-Emission In Znse-Based Quantum-Well Lasers

Spectroscopic work is reviewed which focuses on the microscopic mechanism of gain in ZnSe-based quantum well (QW) lasers, under optical and electrical injection, respectively. In particular, the lasing process in optically pumped ZnCdSe/ZnSe QW lasers at cryogenic temperatures is shown to be entirely an excitonic process. This conclusion is supported by results from resonant pumping experiments and femtosecond pump-probe measurements. A phenomenological model is presented, which can explain the experimental observation rather well. More strikingly for this strong quasi-two-dimensional (2D) exciton system, recent studies on room temperature ZnCdSe/ZnSSe/ZnMgSSe diode lasers show that pairwise electron-hole Coulomb correlation remains relevant in this case as well.