Electrical conduction and phase transitions in vacuum-deposited Cu<SUB>2-x</SUB>S films

The structure, phase transitions and electrical conductivity of Cu<SUB>2-x</SUB>S films deposited by vacuum evaporation at different substrate temperatures were studied. It was found that the deposition parameters significantly affect the composition and the structure of evaporated Cu<SUB>2-x</SUB>S films. The stoichiometry changes from copper rich to copper deficient as the substrate temperature is increased. This is explained in terms of the mechanism of growth of the Cu<SUB>2-x</SUB>S films. The occurence of phase transitions in these films was studied through measurement of the electrical conductivity as a function of temperature. Films deposited at 300 K exist in the &#947; phase and undergo a &#947; &#8594;&#946; phase transition at 325K and a &#946;&#8594;&#945; a phase transition at 350 K. Films deposited at 400 K exhibit only one phase transition, the &#946; &#8594; &#945; a transition at 345K. A very sluggish transition from the orthorhombic to the tetragonal phase of Cu<SUB>1.96</SUB>S was observed at 340 K in films deposited at 475 K. These results were corroborated by electron microscope and diffraction studies on annealed Cu<SUB>2-x</SUB>S films