The room-temperature photoluminescence and electrolyte electroluminescence spectra of polycrystalline samples, in air and in contact with aqueous electrolytes, were studied as a function of the annealing atmosphere and temperature, light intensity and wavelength, applied bias, electrolyte composition and photo-etching treatment. Both luminescence spectra were characterized by 2 broad bands which were centered at about 770 and 920nm and were associated with a red and an infra-red emission, respectively. The red band was attributed to radiative recombination between electrons which were trapped at S vacancies (localized at about 0.79eV below the bottom of the conduction band) and valence-band free holes. The infra-red emission was associated with a radiative recombination process which involved electrons that were trapped at S vacancies and holes that were trapped at Cd vacancies (located at about 0.26eV above the top of the valence band). The luminescence spectrum shape was shown to depend upon the rate of hole injection into the semiconductor, and upon the concentrations of Cd and S vacancies. From an analysis of the red and infra-red band intensities, for both spectra, useful information could be obtained concerning the generation and spatial distribution of vacancies under various annealing treatments.

I.J.Ferrer, P.Salvador: Journal of Applied Physics, 1989, 66[6], 2568-77