Effect of substrate temperature on the optical properties of DC magnetron sputtered copper oxide thin films

Abstract

Copper oxide thin films are deposited on quartz substrates by DC magnetron sputtering and the effect of deposition temperature on the optical properties is examined in detail. Scanning Electron Microscopy (SEM), X-ray diffraction (XRD) analysis, Raman spectroscopy, UV–vis spectroscopy, and four-probe sheet resistance measurements are used to characterize the surface morphology, structural, optical, and electrical properties of the deposited films respectively. Sputter deposition is carried out with the substrate at room temperature and at elevated temperatures between 200 and 300 °C. XRD analysis indicates that the oxide formed is primarily Cu2O and the absorption spectra show a critical absorption edge at around 300 nm. The sheet resistance gradually decreases with increase in deposition temperature, corresponding to an increase in the conductivity of the films. Also observed is an increase in the band gap energy from 2.02 eV for room temperature deposition to 2.35 eV at 300 °C, corresponding to an improved film crystallinity and reduction in defect density. The band gap energy and the variation of sheet resistance with substrate temperature shows that the microstructure plays a vital role in their behavior. These transformation characteristics are of huge technological importance having variety of applications including transparent solar cell fabrication.