Effect of Annealing Temperature On Electrical Properties of Copper Sulfide Thin Film for Optoelectronic Applications

Abstract

The transition metal chalcogenides have attracted enormous attention due to their capability of large-area deposition with various applications in the field of optoelectronics, photoelectric conversion, solar cells, and lithium-ion batteries. The copper sulfide thin films (CuxS,1 ≤ x ≤ 2), being one of the members of transition metal chalcogenide, have been used in several applications such as chemical sensors, photo-absorbing layers, photovoltaics, and lithium-ion batteries. In this research work, the chemical bath deposition method (CBD) has been used to deposit copper sulfide thin film (CuxS) at 27 °C. The molar ratios for copper and sulfur have been taken as 1:5, respectively. The structural, morphological, electrical, and optical properties of as-deposited and annealed CuxS thin films have been investigated. The XRD plots show a mixture of two coexisting polycrystalline phases, namely a digenite phase with Cu1.8S stoichiometry and a covellite phase with CuS stoichiometry up to an annealing temperature of 200 °C. The phase of the CuxS thin film has been entirely transformed into a digenite phase with Cu1.8S stoichiometry and a chalcocite phase with Cu2S stoichiometry at higher annealing temperatures of 300 °C and 400 °C, respectively. The XRD and Raman study confirms that an increase in annealing temperature improves the crystallinity of the CuxS thin film. As the annealing temperature rises, the optical bandgap of the CuxS thin film is found to be decreased. According to the Hall effect measurement, the CuxS thin films are ptype in nature. The current-voltage characteristics of p-CuS/n-Si heterojunction reveal a rectifying nature. This research work aims to examine the effect of annealing temperature on the electrical properties of CuxS thin films for optoelectronic applications by a low-cost deposition method.