Ion beam analysis of Zn 2−2 xCu xIn xS 2 films

Abstract

Thin layers of ZnS–CuInS 2 mixed crystals (called ZCIS) may be promising absorber materials for thin film solar cell applications. The ZCIS films studied here have been grown on (0 0 1) GaP, SiO 2 and (0 1 2) CeO 2/Al 2O 3 substrates with different stoichiometries by pulsed laser deposition (PLD). In order to optimize the film deposition process the thickness, stoichiometry and crystallinity of the films were determined by means of Rutherford backscattering spectrometry (RBS), particle induced X-ray emission (PIXE) and RBS/channeling using a 2 MeV He + ion beam. Furthermore the stoichiometry of the targets used for the PLD was determined with backscattering spectrometry and PIXE using a 2 MeV H + ion beam. A large variation in film thickness was observed and the film stoichiometry did not agree with the PLD-target stoichiometry in general. The element transfer efficiencies from the PLD-target to the deposited film varied substantially for the individual elements. Furthermore, on some films deposited on (0 0 1) GaP a remarkable out-diffusion of Cu into the substrate was found with RBS and confirmed by secondary neutral mass spectroscopy and transmission electron microscopy. RBS/channeling measurements show that mono-crystalline films can be grown on (0 0 1) GaP and (0 1 2) CeO 2/Al 2O 3 substrates, however, they are characterized by a large defect density.