ZnTe-Cu thin films with Cu concentration in the range 3 -9 at % were prepared by co-sputtering using r.f. magnetron sputtering technique. Substrate temperatures between 60 and 320 C and r.f. power of 80 W were used. XRD measurements showed that the films were amorphous below 250 C, while above that temperature a polycrystalline phase with strong preferential orientation of crystallites appears. For undoped films, the XRD spectrum shows the enhancement of the 100 peak of orthorhombic ZnTe polycrystals while for the ZnTe-Cu films evidence was obtained for the presence of Cu_xZn_1-xTe phase with x near 0.20. When the films were prepared in presence of a constant number of Cu pieces distributed over the sputtering area, the resistivity was found to decrease sharply with the rise of substrate temperature. This was attributed to the increase in the solubility of Cu in acceptor sites with increasing temperatures. While the resistivity decreases by nearly 6 decades (indicating a corresponding increase in the concentration of Cu dissolved in acceptor sites) the total Cu concentration measured by the X-ray energy dispersive spectroscopy (EDS) increases by a factor of only 2 with substrate temperature between 60 and 320 ^oC. This was taken to confirm the presence of the majority of Cu in a Cu_xZn_1-xTe phase, thus supporting the results of XRD.
The room temperature transmission and reflectivity were measured in the wavelength range 300≤ λ ≤3000 nm. The absorption coefficient was computed using the Swanepoel method. The energy band gap was determined and found to vary significantly with substrate temperature. This was attributed essentially to the appearance of band tails at the principle bands edges produced by perturbation in the local potential associated with the amorphous modification .For Cu-doped samples, further reduction in E_g is brought about through merging of the Cu acceptor with the valence band

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