Effect of thickness on structural, electrical, and spectral response properties of thermal evaporated CdTe films

The II–VI semiconductor thin films have vast applications in optoelectronics. Cadmium telluride (CdTe) is one such material, which has proved to be useful in the fabrication of solar cells, photodetectors, etc. In the present work, CdTe thin films have been deposited on glass substrates by thermally evaporating CdTe powder under a high vacuum. The optimum film thickness for photovoltaic applications was determined by performing a detailed characterization of the films. The thermal evaporated CdTe films were found to be polycrystalline with a cubic structure. Considerable improvement in the crystallinity was observed with the increase in thickness. The lattice constant, dislocation density, strain, and stress have also been analyzed. The optical properties of the CdTe films have been observed to change with thickness. The maximum optical absorption was found in the near infrared region. The photoluminescence spectra showed a prominent peak, corresponding to the band-edge transition of the CdTe films. The electrical properties of the films were found to improve with thickness. The films yield maximum photocurrent at 820 nm. Based on the detailed characterization, the film thickness of 950 nm was found to be most suitable for photovoltaic application. (author)