Optical, electrical and structural properties of Cu_2Te thin films deposited by magnetron sputtering

摘要

Thin films of Cu_2Te 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_2Te films. Annealing above 300 ℃ resulted in stoichiometric and near stoichiometric Cu_2Te phases, whereas temperatures above 400 ℃ yielded films with single Cu_2Te phase. In contrast, annealing at temperatures of 250 ℃ and below resulted in mixed phases of CuTe, Cu_7Te_5, Cu_1.8Te, and Cu_2Te. Analyses of transmittance and reflectance measurements for Cu_2Te 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 concentrationp = 5.18 ×10~21 cm~-3.