Photoellipsometric studies on CdTe thin films

Photoellipsometry has been used to study the optical properties of CdTe thin films prepared by electrodeposition, physical vapor deposition (PVD) and close spaced vapor transport (CSVT) under different deposition conditions. Pseudodielectric functions (both real and imaginary) have been calculated for samples with and without the pumping beam on. An anomalous peak is observed in the pseudodielectric function spectra of CdTe samples prepared by electrodeposition and CSVT methods. This peak does not appear in CSVT samples prepared under high vacuum (∼ 10−6 mbar) or in samples prepared by PVD. The dependence of this peak on pump intensity, pump beam energy and deposition conditions has been observed. The peak is found to disappear below a threshold intensity (∼ 1 mW/cm2) of pump beam. A plausible reason for the above observations is presence of oxygen in the electrodeposited samples and in CSVT samples prepared in a low vacuum environment.