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The synthesis of nickel silicide thin films via a vapor–solid reaction has been studied by exposing thin (10 nm) Ni films to silane (SiH4). The crystalline phases, the Ni/Si stoichiometric ratios, as well as the surface and interface properties of the resulting silicide films were investigated as a function of the growth parameters such as the SiH4 partial pressure, the reaction temperature, and the exposure time. At low temperature (300 °C), SiH4 exposure led to the self-limiting deposition of Si on Ni by catalytic decomposition of SiH4 but not to silicate formation. Between 350 and 400 °C, phase pure orthorhombic NiSi films were obtained that were formed directly without any apparent intermediate Ni-rich silicide phases. A transformation to NiSi2 occurred at 450 °C and above, and at 500 °C phase pure NiSi2 was obtained. Here, the transient formation of NiSi was observed that transformed into NiSi2 for prolonged SiH4 exposure. The results indicate that the Si solubility governs the phase formation sequence whereas kinetics are determined by Ni diffusion and the reaction rate. Resistivity values of 21 and 36 μΩ cm were found for the NiSi and NiSi2 thin films, respectively, corresponding to the values reported for films obtained by solid-state reactions.

The Cu͑In, Ga͒͑S,Se͒ 2 / Mo interface in thin-film solar cells has been investigated by surface-sensitive photoelectron spectroscopy, bulk-sensitive x-ray emission spectroscopy, and atomic force microscopy. It is possible to access this deeply buried interface by using a suitable lift-off technique, which allows us to investigate the back side of the absorber layer as well as the front side of the Mo back contact. We find a layer of Mo͑S,Se͒ 2 on the surface of the Mo back contact and a copper-poor stoichiometry at the back side of the Cu͑In, Ga͒͑S,Se͒ 2 absorber. Furthermore, we observe that the Na content at the Cu͑In, Ga͒͑S,Se͒ 2 / Mo interface as well as at the inner grain boundaries in the back contact region is significantly lower than at the absorber front surface.