Visible light photodetection enhancement of co-sputtered ZnO:Cu thin films with annealing treatment

Abstract

We study the effect of copper (Cu) dopant on zinc oxide (ZnO) films by direc-current magnetron co-sputtering technique with different Cu power (15 W and 20 W) and thermal annealing on structural, optical, and electrical properties in order to enhance the visible light photodetection performance. X-ray diffraction analysis reveals an improvement of crystallite size by annealing treatment, particularly at high Cu power with crystal growth orientation (002) plane. The surface morphology exhibits various textures and particles sizes, while elemental composition analysis confirms Cu substitution within the ZnO matrix. Fourier transform infra-red analysis indicates strengthened Zn-O bond vibrations following annealing, with a shift attributed to Cu doping. Additionally, the bandgap energy narrows to 2.94 eV, and photoluminescence measurements reveal an increased near band edge emission and a reduction in defect density. According to current-voltage measurements, Cu-doped ZnO films at higher Cu power with annealing treatment demonstrate twofold higher photosensitivity and threefold higher responsivity compared to pristine ZnO. In this study, increased crystallite size, reduced structural defects, and narrowed bandgap energy primarily contribute to enhanced sensitivity to visible light. Furthermore, the reduced Schottky barrier height indicates improved conductivity, further optimizing photodetection efficiency. The results confirm that Cu-doped ZnO films processed at 20 W Cu power and thermal annealing exhibit superior photo-detecting performance, making them highly suitable for functional optoelectronic devices.