Enhancement of Mobility of Chemically Prepared CuS Thin Film by Post-Deposition Annealing

Abstract

In the modern era, transition metal chalcogenides have captivated much attention due to their capability of large-area deposition, and the possibility of deposition on various surfaces with a variety of applications in optoelectronic, photoelectric conversion, solar cell, lithium-ion batteries, biomedical devices, electroconductive coatings, and microwave shielding coatings. In this work, covellite copper sulfide (CuS) thin film has been deposited on the glass substrate by the low-cost chemical bath deposition (CBD) method with 1:3 molar ratio of copper and sulfur for 4 hr at 70 °C. The post-deposition annealing was carried out at 100 °C and 200 °C. The structural, electrical, and optical properties of annealed CuS thin film have been investigated, where XRD confirms the presence of the covellite phase of copper sulfide thin film with the evolution of (102) and (110) planes. Raman spectroscopy reveals a prominent peak at 475 cm-1 , depicting the formation of the covellite phase of copper sulfide thin film. The crystallinity of CuS thin film is found to be increased with an increase in the annealing temperature. The optical bandgap is decreased to 2.20 eV with an increase in annealing temperature. The Hall effect measurement system has revealed the p-type nature of CuS thin film. The carrier concentration of CuS thin film is found to be decreased with an increase in annealing temperature. The mobility of CuS thin film has been enhanced up to 55.13 cm2 /V.s with an increase in annealing temperature due to an increase in crystallite size. Hence, the resistivity of CuS thin film decreases with an increase in annealing temperature due to an increase in mobility of charge carriers. The current-voltage plot of CuS thin film reveals the ohmic nature of CuS thin, ensuring a good metal-semiconductor contact with the free movement of charge carriers between metal and semiconductor. The CuS thin film at 200 °C exhibits the highest photocurrent under the illumination of visible light. The CuS thin film, annealed at 200 °C, possesses a carrier concentration of 5.8×10 18 cm-3 , and mobility of 55.13 cm2 /V.s, optical bandgap of 2.20 eV; which could be a suitable candidate for fabrication of various optoelectronic devices.