Characterization of Cu-doped Cd1−xZnxTe thin films sputtered from multiple targets

• Cd1−xZnxTe: Cu thin films sputtered simultaneously from multiple targets.
• Effects of Cu concentration on the properties of thin films.
• Abnormal dark conductivity as function of temperature was observed and explained.

Cd1−xZnxTe (CZT) has a band gap tailored continuously from 1.45 to 2.26 eV and is therefore a potential candidate for the top cell in tandem solar cell applications. In this paper, Cd0.6Zn0.4Te: Cu thin films were fabricated by RF magnetron sputtering from three targets (ZnTe, CdTe and Cu). X-ray diffraction patterns show that the as-deposited films were the cubic phase with a preferred (111) orientation. The strain formed in the Cu-doped Cd0.6Zn0.4Te thin films increased with increasing Cu concentration. All the films had a band gap of around 1.72 eV, but an apparent decrease of transmittance occurred in heavily doped ones.5.70 at% doped Cd0.6Zn0.4Te: Cu films presented only less than 10% transmittance. The conductivity of Cd0.6Zn0.4Te: Cu films at room temperature increased with Cu concentration in the range of 10−4∼100 S cm−1. The temperature dependence of dark conductivity for Cu-doped samples did not follow the Arrhenius behavior and a deviation appeared on the warming curve. The activation energy of the dark conductivity for doped and undoped CZT films was calculated between 0.15 and 0.80 eV. Finally, CdS/CZT junctions were prepared. These devices were found to indicate the photovoltaic effects. And the device performance was analyzed.