The Effect of Annealing Temperature and Reactive Gases on Optical Properties of Cu₂O Thin Films

Abstract

The Cu 2 O thin films were synthesized by using RF sputtering technique. Comparisons were made with films created by deposition at room temperature followed by thermal annealing between 100°C and 400°C and using different gases, oxygen (O 2 ) (oxidizing and reactive gas) and nitrogen (N 2 ) (inert gas), besides air. The thickness of the thin films was kept constant, around 2000 Å (Angstrom). In addition, the RF power and pressure deposition were kept constant, as well. The thin films were evaluated for a range of wavelengths between 200 nm and 400 nm (Ultra Violet spectrum), 400 nm and 700 nm (Visible spectrum), 700 nm and 800 nm (Infrared spectrum) for both, optical transmittance and photoluminescence. From the experimental results, the higher annealing temperature and the introduction of nitrogen (N 2 ) gas produced the following results: the optical bandgap for the Cu 2 O was found to be 2.23 eV and photoluminescence peaks were around 551 nm and 555 nm, which matched the theoretical analyses. Overall, there was a decrease in the optical bandgap of the Cu 2 O from 2.56 eV at room temperature to 2.23 eV for the film annealed in nitrogen gas at 400°C. This indicates that the Cu 2 O is a potential candidate in solar cell applications.