Phases in copper–gallium–metal–sulfide films (metal=titanium, iron, or tin)

The incorporation of metal impurities M (M = Ti, Fe, or Sn) into CuGaS2 films is investigated experimentally as a function of impurity concentration. Films are synthesized by thermal co-evaporation of the elements onto glass/Mo substrates heated to 400 °C–570 °C. The compositions of the resulting films are measured by energy-dispersive X-ray spectroscopy and the structures of the present phases are studied by X-ray diffraction. The formation of Cu–M–S ternary phases is observed in a wide range of conditions. Films of Cu–Ga–Ti–S, synthesized at 500 °C, show the presence of a cubic modification of CuGaS2 and Cu4TiS4. Alloying of CuGaS2 and tetragonal Cu2SnS3 is observed for substrate temperatures of 450 °C. A miscibility gap opens at 500 °C and above with separate Sn-rich and Ga-rich phases. Similarly, alloys of CuFeS2 and CuGaS2 are only found in Cu–Ga–Fe–S films synthesized at lower substrate temperature (400 °C), whereas at 500 °C a miscibility gap opens leading to separate Fe-rich and Ga-rich phases.