Conversion of chemically deposited CuS thin films to and by annealing

Abstract

Thin films of copper sulphide with thickness up to m were deposited at C on glass substrates from a solution containing copper(II) chloride, sodium thiosulphate and dimethylthiourea. As prepared and after annealing at C in (100 millitorr), these films showed x-ray diffraction patterns matching that of the mineral covellite (CuS). Annealing the films for 1 h each at C and C in nitrogen resulted in their conversion to S (digenite) and S (chalcocite), respectively. The reduction in sulphur content of the films is evident in the x-ray florescence spectra. The sheet resistance of the films varied with annealing temperature. For a film of m thickness, the observed sheet resistance values are: (as prepared), (C), (C) and (C). The low sheet resistance (and thus the high conductivity, ) leads to a high near-infrared reflectance for the films, 65% (CuS) and 40% (S), at a wavelength of 2500 nm. Analyses of the optical band gap of the films indicate an indirect gap of 1.55 eV for CuS and S and 1.4 eV for S.