Electrical properties of Te-rich, Cd-rich and hydrogen-exposed polycrystalline CdTe thin films

Abstract

Polycrystalline films of CdTe, stoichiometric, Te-rich, and Cd-rich, were grown using a vacuum evaporation technique on glass substrates kept at room temperature. The as-grown films were exposed to hydrogen gas at high pressure (200-500 PSI). Measurements of DC conductivity in the temperature range 77-300K, X-ray diffraction studies and electron probe microanalyses were made on these films. The conductivity data for the stoichiometric, Te-rich and Cd-rich films in the low temperature region have been analysed for variable range hopping conduction on the basis of Mott's model. The analysis of the high temperature conductivity data for Te-rich and hydrogen-exposed films has been based on Seto's model of thermionic emission. It is found that addition of Te and Cd improves the conductivity of the films by four and six orders of magnitude respectively. However, the density of trap states near the Fermi level, N(EF), also increases with increase of Cd and Te content. In the case of hydrogen-exposed films the conductivity decreases with increase of gas pressure.