Impact of laser irradiation on the properties of zinc oxide thin films deposited by radio frequency magnetron sputtering

Abstract

Zinc Oxide (ZnO) thin films have been shown to have excellent structural, morphological, optical and electrical properties, which has made them candidates for use in photovoltaic devices.

These properties can be improved by adding doping materials, controlling times and conditions of the deposition, this can result in toxic and expensive materials, long manufacturing times, specific atmospheric conditions, which can increase production costs and affect the environment. One possibility of property improvement is to only use thermal treatment, such as laser radiation, a more selective, localized, and faster method compared to traditional furnace annealing.

In this research, ZnO thin films were produced using radio frequency magnetron sputtering and subjected to treatment with a continuous wave carbon dioxide laser to enhance their properties. In X-ray Diffraction, the irradiated ZnO thin films showed a wurtzite structure (zincite) with a preferred orientation in the plane (002). Raman spectroscopy revealed the activation of an unusual B₁^high-B₁^low mode in the irradiated ZnO films. Laser irradiation formed microbumps in the surfaces of the treated thin films, as a form of stress relief and a decrease in surface roughness, which were observed in scanning electron microscopy and atomic force microscopy, respectively.

Furthermore, the ZnO thin films exhibited high transparency in the visible spectrum, with band gap values ranging from 3.25 to 3.28 eV. The photoresponse of these films was improved with laser treatment at 4 W, 266 W/cm², and 2.5 mm/s. This study offers valuable insights into the fabrication of high-quality crystalline ZnO thin films by using continuous far-infrared laser irradiation as a heat treatment process, which could be applied in solar cell technology.