Radiofrequency-plasma-deposited hydrogenated fluorinated silicon-carbon alloy films

Properties of ${\mathrm{Si}}_{1\mathrm{-}\mathrm{x}}$ ${\mathrm{C}}_{\mathrm{x}}$:F:H films prepared from silicon tetrafluoride–carbon tetrafluoride–hydrogen gas mixtures by radiofrequency-plasma-enhanced chemical-vapor deposition are reported. The dark conductivity and its activation energy are found to be very sensitive to the proportion of hydrogen. The infrared absorption spectra suggest a microcrystalline structure in films prepared at low hydrogen dilution. This has been confirmed by the transmission electron microscopy. At larger hydrogen dilution, photosensitive, amorphous material is formed. The constant photocurrent spectra and space-charge-limited current studies combine to reveal a low density of shallow as well as deep defects. The photoconductivities of these films are found to be superior to those prepared without fluorine for band gaps larger than 1.85 eV. The material properties may be understood in terms of the relative concentrations of ionic and atomic hydrogen and fluorine in the plasma and at the growth surface.