Effect of growth temperature, thermal annealing and nitrogen doping on optoelectronic properties of sputter-deposited ZnTe films

Thin films of zinc telluride were grown on glass substrate at different temperatures by magnetron sputtering. Nitrogen-doped films were also prepared at different doping levels. Films underwent a post deposition thermal annealing at low pressure of nitrogen. The film structure, optical and electrical properties were studied using various techniques. The results revealed that the films are composed from nano-size grains (3 – 19nm) with cubic lattice structure. The grain growth during deposition is thermally activated with the activation energy of 108meV. Direct optical transitions occurring from the valence band and also from the spin-orbit valence band to either a band gap defect level (for as-grown films) or to the conduction band (for annealed films) have been observed. The valence band split energy is found to be in the range 0.82 – 1.10eV. The defect level, likely related to oxygen impurities, is located 1.77eV above the valence band edge. The band gap energy of the annealed films is in the range 2.13 – 2.20eV and the films doped with nitrogen, at optimum condition, have a free hole concentration and mobility of 2.9×1018cm−3 and 1.4cm2V−1s−1, respectively. •Undoped and nitrogen doped ZnTe films were grown on glass by sputtering technique.•Growth temperature varied in the range 35– 305°C.•Optimum doping was achieved at the N2/(N2+Ar) flow rate ratio of 2%.•At optimum condition 2.9×1018holes/cm3 with mobility 1.4cm2V−1s−1 were obtained.•The split valence band and oxygen defects contribute to the absorption of light.