On the structural properties of a-Si1−xCx:H thin films

Abstract

The structural and chemical properties of hydrogenated amorphous silicon carbide (a-Si1−xCx:H) thin films, deposited by plasma-enhanced chemical-vapor deposition, were determined by extended x-ray absorption fine structure (EXAFS), x-ray-absorption near-edge spectroscopy (XANES), small-angle x-ray scattering, Fourier transform infrared (FTIR) spectroscopy, Auger electron spectroscopy, and visible spectrometry. The EXAFS and XANES results show the crucial influence of the ‘‘starving’’ plasma deposition conditions on the structural properties of wide-gap a-Si1−xCx:H films and are consistent with the FTIR and optical-absorption data. The first-neighbors distance for alloys with smaller carbon content or deposited at higher silane flow are very close to the mean Si–Si distance obtained for a-Si:H. On the other hand, the EXAFS spectra of films with higher carbon content (x≳50 at. %) and deposited under ‘‘starving’’ plasma regime show Si–C distances similar to crystalline SiC (c-SiC). The presence of a typical c-SiC resonance in the XANES spectra of the same samples is evidence that the material has a chemical order close to that of c-SiC.