Optical, electrical and structural properties of Cu2Te thin films deposited by magnetron sputtering

Abstract Thin films of Cu 2 Te were deposited, at room temperature, on glass substrates by magnetron sputtering from independent Cu and Te sources. This work presents the effect of annealing temperature on the optical, structural, and electrical properties of sputtered Cu 2 Te films. Annealing above 300 °C resulted in stoichiometric and near stoichiometric Cu 2 Te phases, whereas temperatures above 400 °C yielded films with single Cu 2 Te phase. In contrast, annealing at temperatures of 250 °C and below resulted in mixed phases of CuTe, Cu 7 Te 5 , Cu 1.8 Te, and Cu 2 Te. Analyses of transmittance and reflectance measurements for Cu 2 Te indicate that photon absorption occurs via indirect band transitions for incident photons with energy above the band gap energy and free carrier absorption below the band gap energy. The determined indirect band gap was 0.90 eV and its associated phonon energy was 0.065 eV. Optical phonon scattering was identified as the mechanism through which the momentum is conserved during absorption by free carriers. Electrical measurements show p -type conductivity and highly degenerate semiconducting behavior with a hole carrier concentration p = 5.18 × 10 21 cm − 3 .