Gain spectroscopy and plasma recombination in CdS

Abstract The spectral dependence of optical amplification (gain) is measured in highly excited CdS as function of sample temperature, excitation intensity and polarization. The results indicate the existence of an electron hole plasma with a density of 2,8·10 17 cm -3 , a critical temperature of 75 K and a binding energy relative to the free A Γ6 exciton of approximately 9 meV. The spectral dependence of the gain is consistent with a momentum conserving recombination of the electron hole pairs in the plasma. We compare our experimental findings with some recent results of other authors.