Electrical conductivity measurements in evaporated tin sulphide thin films

Abstract

Tin sulphide (SnS) has been evaporated on to substrates maintained at fixed temperatures in the range 50-300°C. X-ray diffraction measurements have shown that the films deposited at the lower substrate temperatures are non-stoichiometric, containing higher sulphides of tin, but that those deposited at 300°C consist essentially only of SnS. Film conductivity increased in the range 0·5-20 Sm-1 as the substrate temperature during deposition increased from 50°C to 250°C, this effect being attributed to the changing film composition. Films deposited at 50°C and 150°C showed thermally activated conductivity at temperatures above 220-250 K, with activation energies EB; of 0·12 eV and 014eV, respectively. At lower temperatures both conductivity and activation energy were considerably lower, consistent with hopping via localized states. The conductivity is modified after prolonged cooling to 160K, although the mechanism of this process is not understood