Study of Urbach tail, bandgap energy and grain-boundarycharacteristics in CdS by modulated photocurrentspectroscopy

Abstract

Thin cadmium sulfide films were deposited on glass substrates bychemical bath deposition method. The planar photoconductivitywas measured as a function of the incident photon energy atdifferent temperatures.From the fit of experimental results to the existing models,various optoelectronic parameters of CdS, including those relatedto the temperature dependence of bandgap and the Urbach tail,were evaluated. The measurement technique also helped toevaluate the donor concentration (3×1016 cm-3) in the sample used.In addition to the existing models, the photoconductivity modelwas extended to account for the effect of incident light inlowering the grain-boundary potential barrier. This allowed themeasurement of both, the grain-boundary potential barrier (0.02-0.04 eV)and the energy of the dominant defect level at grain boundaries(0.11-0.13 eV).