Electrical and optical properties of r.f. co-sputtered ZnTe-Cu thin films

摘要

ZnTe-Cu thin films with Cu concentration in the range 3-9 at% were prepared using r.f. magnetron co-sputtering. XRD results showed that the films were amorphous below 250 ℃, 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-x)Te phase with x near 0.20. The results of electrical measurements supports the view that the majority of Cu is in the Cu_xZn_(1-x)Te phase. The room temperature transmission and reflectivity were measured in the wavelength range 300 nm ≤ λ ≤ 3000 nm. The energy band gap was determined and found to vary significantly with substrate temperature. This was attributed 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 Eg is brought about through merging of the Cu acceptor density-of-states with the valence band.