Temperature dependence of the optical transitions in CdTe thin film – Investigation with photoresponse spectra

The CdTe thin films have been prepared by electrochemical method from a bath solution containing cadmium sulfate and tellurium dioxide. Schottky devices of the type Au/CdTe were prepared and the spectral response of the device has been investigated. The direct and indirect transitions in the 1.3–1.6 eV region were calculated from the normalized spectral response data. The temperature dependence of the band gap have been investigated and correlated with the theory. The band gap of CdTe at absolute zero temperature is estimated as 1.61 eV and that the rate of change of Eg with temperature is calculated as −0.4 meV/K. The 1.407 eV indirect transition involves a trap level near the conduction band edge. The indirect transition also exhibits temperature dependence.