Investigating the optical band gap and crystal structure of copper sulphide and copper selenide thin films deposited by chemical bath deposition

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Thin films of CuS and CuSe have been successfully deposited using the CBD technique. The reagents used for the deposition of CuS were copper chloride, thiourea and ammonia. CuSe was deposited from chemical baths containing copper chloride, sodium selenosulphate and ammonia. The pH deposition temperature and time were optimized for deposition. The optical band gap and the structure of the as-deposited and annealed films were studied using optical absorption spectroscopy and powder x-ray diffraction analysis. The crystal structure of the as- deposited CuS films showed the presence of several phases with covellite being the dominant phase. After annealing at 673 K, only the copper sulphate pentahydrate phase was observed. The band gap varied from 1.6 eV for the as- deposited sample to 2.2 eV after annealing at 673 K. Optical studies on CuSe showed that the as-deposited films had two band gaps of 1.2 and 1.4 eV suggesting the presence of more than one phase. This feature was also observed in the samples annealed at 473 K, but samples annealed at 573 K and 673 K had only one band gap of 2.2 eV. The crystal structure of the as-deposited CuSe films showed the presence of several phases with the umangite being the dominant phase. However, after annealing at 673 K, the dominant phase was krutaite, suggesting a possible phase transformation.
A thesis submitted to the Department of Physics, Kwame Nkrumah University of Science and Technology, in partial fulfillment of the requirement for the degree of MASTER OF PHILOSOPHY (SOLID STATE PHYSICS).