Excitation photon energy dependence of photoluminescence in CdTe thin films

We report the photoluminescence spectra of CdTe polycrystalline thin films at 10 K as a function of the exciting photon energy in the 1.59 to 1.71 eV range. Our results indicate that the ratio of the maximum intensity of the bound exciton band (I-b at approximate to 1.59 eV) to that of the defect ba nd (I-d at approximate to 1.45 eV) shows resonances in this range. Above th e band-gap region (E-g = 1.606 eV) and near E-g + hw(LO) (With hw(LO) the L O-phonon energy) a first resonant feature is detected. This behavior is att ributed to the efficient emission of LO-phonons during the thermalization p rocess of the created photocarriers in their corresponding bands. Below and near E-g a second and lower resonance is also present, which can be explai ned in terms of the direct formation of bound excitons.