INFLUENCE OF COULOMB CORRELATIONS ON GAIN AND STIMULATED-EMISSION IN (ZN,CD)SE ZN(S,SE)/(ZN,MG)(S,SE) QUANTUM-WELL LASERS/

The influence of Coulomb correlations on gain and stimulated emission in (Zn,Cd)Se/Zn(S,Se)/(Zn,Mg)(S,Se) quantum-well lasers is studied und er stationary conditions. Systematic temperature-dependent measurement s under application of different spectroscopic techniques were perform ed. Optical gain is measured by means of the variable stripe-length me thod, whereas excitonic bleaching under lasing conditions is analyzed through two-beam photoluminescence excitation (PLE) spectroscopy. Furt hermore, complementary low-density single-beam PLE spectra are recorde d in order to study the temperature dependence of the heavy-hole excit on peaks. The experimental data as a whole are shown to be inconsisten t with any of the usually quoted excitonic models for lasing in II-VI heterostructures. The experiments are more adequately explained by a s trongly correlated electron-hole plasma described by Bethe-Salpeter-li ke equations for the optical response and recombination rates in the e xcited medium. The nonequilibrium Green's-function approach used consi stently includes, at a microscopic level, band structure, quantum-conf inement, and many-body effects.