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 - 19 nm) with cubic lattice structure. The grain growth during deposition is thermally activated with the activation energy of 108 meV. 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 - 1.10 eV. The defect level, likely related to oxygen impurities, is located 1.77 eV above the valence band edge. The band gap energy of the annealed films is in the range 2.13 - 2.20 eV and the films doped with nitrogen, at optimum condition, have a free hole concentration and mobility of 2.9 × 1018 cm− 3 and 1.4 cm2 V− 1 s− 1, respectively.