ROLE OF BIEXCITONS IN THE STIMULATED-EMISSION OF WIDE-GAP II-VI QUANTUM-WELLS

On high-quality ZnCdSe/ZnSe quantum wells the occurrence of a new emis sion feature energetically below the exciton transition is demonstrate d from which stimulated emission and gain emerge at elevated excitatio n levels (10 kW/cm(2)). Application of a magnetic field allows us to d istinguish this feature from bound excitons and evidence its biexciton nature. Subpicosecond excite-and-probe measurements reveal the scenar io of exciton-exciton interaction in the presence of alloy disorder (l ocalization). A model accounting for bound and antibound two-exciton s tates provides good agreement with the experimental data.