Study of Urbach tail, bandgap energy and grain-boundary characteristics in CdS by modulated photocurrent spectroscopy

Thin cadmium sulfide films were deposited on glass substrates by chemical bath deposition method. The planar photoconductivity was measured as a function of the incident photon energy at different temperatures. From the fit of experimental results to the existing models, various optoelectronic parameters of CdS, including those related to the temperature dependence of bandgap and the Urbach tail, were evaluated. The measurement technique also helped to evaluate the donor concentration (3 x 10(16) cm(-3)) in the sample used. In addition to the existing models, the photoconductivity model was extended to account for the effect of incident light in lowering the grain-boundary potential barrier This allowed the measurement of both, the grain-boundary potential barrier (0.02-0.94 eV) and the energy of the dominant defect level at grain boundaries (0.11-0.13 eV).