Crystalline structure of chemically deposited thallium sulfide thin films

Abstract

Thin film coatings of Tl 4S 3 or Tl 2S of 100–750 nm in thickness have been deposited from a mixture of citratothallium complex and thiourea solutions at 35 or 50°C by chemical bath deposition on glass substrates coated with a thin ZnS film. Upon heating in a nitrogen atmosphere at 300°C, all the films, irrespective of the initial composition, convert to crystalline Tl 2S. The variation of the optical absorption coefficient with photon energy for a typical sample of Tl 2S suggests forbidden direct transition as the mechanism for optical excitation. All the films, ‘as prepared’ as well as those heated to 300°C, are photoconductive. In the heated films dark conductivity is typically 7.5×10 −6 Ω −1 cm −1 and photoconductivity, 5×10 −5 Ω −1 cm −1.