EXCITONS AND ELECTRON-HOLE PLASMA PHASE IN ZN1-XCDXSE ZNSE MULTIPLE-QUANTUM-WELL LASER STRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY/

The exciton stability in Zn1-xCdxSe/ZnSe multiple quantum wells has be en investigated by absorption and magneto-luminescence spectroscopies in undoped and modulation-doped samples. The well width and the compos ition dependence of the exciton binding energy has been determined exp erimentally and compared with the value obtained with theoretical calc ulations. The absorption saturation has been investigated in modulatio n-doped samples as a function of the sheet carrier density. The excito n stability has been correlated to the actual lasing mechanism in samp les with different structure and composition. Free-carrier recombinati on dominates the stimulated emission of Zn1-xCdxSe quantum wells with relatively low exciton binding energy, whereas a dominant excitonic ch aracter is found in the lasing of deep and narrow quantum wells. Stimu lated emission experiments in high magnetic fields performed on variou s samples confirm this attribution.