Cu x SnS x+1 (x = 2, 3) thin films grown by sulfurization of metallic precursors deposited by dc magnetron sputtering

We report the results of the growth of Cu‐Sn‐S ternary chalcogenide compounds by sulfurization of dc magnetron sputtered metallic precursors. Tetragonal Cu 2 SnS 3 forms for a maximum sulfurization temperature of 350 °C. Cubic Cu 2 SnS 3 is obtained at sulfurization temperatures above 400 °C. These results are supported by XRD analysis and Raman spectroscopy measurements. The latter analysis shows peaks at 336 cm ‐1 , 351 cm ‐1 for tetragonal Cu 2 SnS 3 , and 303 cm ‐1 , 355 cm ‐1 for cubic Cu 2 SnS 3 . Optical analysis shows that this phase change lowers the band gap from 1.35 eV to 0.98 eV. At higher sulfurization temperatures increased loss of Sn is expected in the sulphide form. As a consequence, higher Cu content ternary compounds like Cu 3 SnS 4 grow. In these conditions, XRD and Raman analysis only detected orthorhombic (Pmn21) phase (petrukite). This compound has Raman peaks at 318 cm ‐1 , 348 cm ‐1 and 295 cm ‐1 . For a sulfurization temperature of 450 °C the samples present a multi‐phase structure mainly composed by cubic Cu 2 SnS 3 and orthorhombic (Pmn21) Cu 3 SnS 4 . For higher temperatures, the samples are single phase and constituted by orthorhombic (Pmn21) Cu 3 SnS 4 . Transmittance and reflectance measurements were used to estimate a band gap of 1.60 eV. For comparison we also include the results for Cu 2 ZnSnS 4 obtained using similar growth conditions. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)