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 been investigated by absorption and magneto-luminescence spectroscopies in undoped and modulation-doped samples. The well width and the composition dependence of the exciton binding energy has been determined experimentally and compared with the value obtained with theoretical calculations. The absorption saturation has been investigated in modulation-doped samples as a function of the sheet carrier density. The exciton stability has been correlated to the actual lasing mechanism in samples with different structure and composition. Free-carrier recombination dominates the stimulated emission of Zn1-xCdxSe quantum wells with relatively low exciton binding energy, whereas a dominant excitonic character is found in the lasing of deep and narrow quantum wells. Stimulated emission experiments in high magnetic fields performed on various samples confirm this attribution.