EXCITONIC NONLINEARITIES IN WIDE-GAP II-VI MULTIPLE-QUANTUM WELLS

We report a comprehensive study of excitonic nonlinearities in Zn1-xCd xSe/ZnSe multiple quantum wells under optical and electrical excitatio n. The stability of the heavy-hole exciton is studied as a function of Cd concentration by using pump and probe transmission spectroscopy. T he heavy-hole exciton absorption peak is investigated as a function of the intensity of the pump beam until the exciton bleaching is reached . The experimental results are fitted with a theoretical model which i ncludes band-gap renormalization, phase space filling and density depe ndent lifetime broadening. The correlation of these results with stimu lated emission measurements performed also in magnetic field up to 8 T , allowed us to elucidate the role of excitons and free carriers in th e lasing process in Zn1-xCdxSe/ZnSe multiple quantum wells. Electric f ield induced effects are also studied in order to elucidate the role o f quantum confined Stark effect on the optical modulation. Further ins ight in the nonlinear optical properties of excitons has been obtained by photoluminescence measurements under external bias.