Photoconductivity Study of Sputter-Deposited $Cu_2O$ Films

Cuprous oxide $(Cu_2O)$ thin films were deposited by radio frequency sputtering technique on fused silica substrates. The X-ray diffraction study of the $Cu_2O$ samples showed reflections from (111) and (200) planes of cubic $Cu_2O$. The samples were then annealed at 1008 K in nitrogen $(N_2)$ atmosphere. Annealed samples indicated strain relaxation. The samples were then characterized optically by measuring the transmittance using an ultraviolet-visible-near infrared photospectrometer. The band gap of the as-deposited samples were found to be ≈ 2.1 eV, whereas the annealed samples had a band gap of ≈ 2.6 eV. The transient photocurrent decay measurements of the annealed films indicated slow non-exponential power law decays in several time windows, indicating multiple trapping of the carriers in the deep defects within the band gap. The steady-state photo and dark current measurement and persistent photocurrent (PPC) was carried out on the annealed samples. In general, the photocurrent was found to be much smaller than the dark current. The steady-state and transient photocurrent measurements were utilized to determine the carrier lifetime-mobility product, 〈μτ 〉 of the samples and to determine the carrier mobility, 〈μ 〉.