Compositional and structural properties of hydrogenated amorphous silicon-carbon films prepared by ultra-high-vacuum plasma-enhanced chemical vapour deposition with different carbon sources

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Abstract
Hydrogenated amorphous silicon-carbon films were deposited by ultra-highvacuum plasma-enhanced chemical vapour deposition in silane + methane and silane + acetylene gas mixtures. Both types of film were compared with respect to their compositional, optical and structural properties. They have an optical gap in the range 2·3–3·3 eV for [C]/[C + Si] between 0·2 and 0·7 and possess high uniformity. The deposition rate of C2H2-based films is 4–5 Å s−1, one order of magnitude higher than Ch4-based films having large bandgap. By infrared (IR) spectroscopy, marked differences in carbon and hydrogen incorporation have been found for the films grown using the two different carbon sources. Analysis of the IR spectra reveals, among the most important structural characteristics, that the films grown from the SiH4 + Ch4 plasma have a higher concentration of Si-C bonds than those grown from SiH4 + C2H2, and that C2H2-based alloys allow the formation of carbon clusters during the growth of the films. Considerations of the average coordination number, the chemical bonding and the degree of chemical order are also reported and discussed.

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