OPTICAL AND ELECTRICAL-PROPERTIES OF COPPER SULFIDE FILMS OF VARIABLE COMPOSITION

Four kinds of copper sulfides of different chemical compositions were chemically deposited and examined for their optical and electrical characteristics. Electroless chemical deposition from aqueous copper thiosulfate baths in acidic media was used to deposit thin films of Cu2S, Cu1.8S, Cu1.4S, and CuS on glass, polyester, or metal substrates. Rutherford back scattering analysis was used to determine the chemical composition of the films. The optical characteristics of the films were studied in the UV-VIS-NIR region, between 0.3 and 2.5 mu m Cu2S films were found to be highly transmissive throughout the spectral region 0.5-2.5 mu m. The transmission in the near-infrared region (0.8-2.5 mu m) decreased as the chemical composition approached the stoichiometry of CuS, which was found to be highly absorptive for the near-infrared radiation. All films displayed high electrical conductivity, with the CuS film being the most conductive and conductivity decreasing toward the copper-rich phase, Cu2S. All films were found to be p-type semiconductors. The optical energy band gaps of the films were also studied and it is shown that the values can differ, depending on the method of determination. Some practical applications of these films are also discussed. (C) 1995 Academic Press, Inc.