Electrical properties and spectroscopic ellipsometry studies of covellite CuS thin films deposited from non ammoniacal chemical bath

In this paper, CuS thin films with good adherence and of different thickness in the range of 450-800 nm were prepared by chemical bath deposition method without using ammonia. The precursor solution was made by mixing copper (II) chloride, sodium thiosulfate, dimethylthiourea and deionized water. The bath temperature was kept at 65 degrees C and deposition time was varied from 3 h to 6 h with an increment step of 1 h to obtain different film thickness. A post annealing step in N-2 atmosphere at 200 degrees C for 30 min was employed to improve the crystallinity and grain recrystallization of the films. X-ray diffraction and Raman scattering analysis revealed a hexagonal covellite structure in the films. However, the formation of secondary phases in trace amount and lower degree of crystallinity were detected for lower deposition time. FESEM images showed the formation of elongated needle-like particles which were distributed uniformly over the surface. The average length of the particles are in the range of 450-500 nm. The effect of deposition time on the optical properties was evaluated and the optical band gap values were found to be in the range of 2.26-2.55 eV. Variable-angle spectroscopic ellipsometry studies were performed to determine the optical constants including inter-band transitions in CuS films. The dependence of deposition time on the electrical properties of the films were evaluated by Hall Effect measurement showing a systematic decrease in film resistivity with increased deposition time.