Preparation of CuO thin films by thermally oxidized metallic Cu films for CdS/CuO heterojunction diode

Abstract

Copper thin films were deposited on glass substrates using thermal evaporation in vacuum and then thermally oxidized in air at temperatures of 100-500°C. XRD patterns showed the formation of a fine grain Cu2O phase at 300°C and a CuO phase at 400°C, respectively. Crystallinity and grain size improved with increasing oxidation temperature. The energy gap of the samples evaluated from absorption measurements was 2.10-2.23 eV. Important electrical parameters of the CuO thin films obtained from oxidizing at 500°C were resistivity of 8.53x103 Ω•cm, carrier concentration of 7.60x1013 cm-3, and mobility of 6.22 cm2/V•s. A prototype of a CdS/CuO thin-film heterojunction diode was successfully prepared by thermal evaporation of CdS thin films on CuO thin-film substrate in a vacuum. The obtained device exhibited a good rectifying behavior from I-V characteristics. Junction parameters calculated using I-V data were barrier height of 5.190 eV, ideality factor of 0.520, and series resistance of 3.87 O. Impedance spectroscopy of the device was investigated at temperatures of 25-60°C. The real and imaginary parts of the complex impedance changed with the temperature and frequency. The experimental results suggested that the device was a good candidate for photovoltaic devices with low thermal budget and low product cost.