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

Abstract

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 (3×1016 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 (0.02-0.04 eV) and the energy of the dominant defect level at grain boundaries (0.11-0.13 eV).

Aerosol assisted chemical vapor deposition (AACVD) of CdS thin films from heterocyclic cadmium(II) complexes

“…The UV-Vis absorption results indicate that, with increasing the annealing temperature from 350 to 450°C, band gap changes one insignificant. The band gap energy of the films was estimated to be 2.38 ± 0.04 eV from the Tauc plot [43]. These observations are similar to those of CdS thin films deposited when complex (2) was used as single source precursor, however the 2.…”

Photophysics, photoelectrical properties and photoconductivity relaxation dynamics of quantum-sized bismuth(III) sulfide thin films

“…The study of the phenomenon of photoconductivity is an effective method for understanding band structures of investigated semiconducting materials [6,28,37,[39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57]. Using the photoconductivity measurements, information about kinetics of generation, transport and recombination of charge carriers, as well as the density and nature of states in the energy gap due to the presence of impurities and defects can be obtained [39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56][57].…”

Optical Properties of RF Sputtered Samarium Oxide Thin Films

“…Figure 4 displays the spectral behavior of the absorption coefficient α showing a slight increase in the intensity of α with a red shift in the absorption edge by increasing the gas pressure. An absorption tail can be practically observed in the absorption coefficient which is a feature of most optical data for amorphous and polycrystalline semiconductors [48]. Some tail states lie in the gap region which arise due to the presence of defects in the material.…”

“…Therefore, the absorption of photons occurs even at energies lower than E g . The absorption tail can be determined mainly due to structural disorder existing at the grain boundaries [48]. In this region the absorption coefficient α is said to obey Urbach role [49] [50].…”