Correlation between the optoelectronic properties and the structure of hydrogenated amorphous silicon-carbon films grown from a C2H2 gas source

Hydrogenated amorphous silicon-carbon alloys (aSi(1-x)C(x):H) with an optical gap in the range 2.0-2.45 eV have been grown by plasma-enhanced chemical vapour deposition from C2H2 + SiH4 gas mixtures employing low-purity (99.95%) sources. By changing the acetylene percentage in the plasma from 0.8% to 20% the relative carbon content [C]/[C + Si] in the films was varied between 0.09 and 0.35, as deduced from Rutherford back scattering. Optical, electrical and defect data have been obtained. We have shown that the physical properties of C2H2 based films, without any deposition condition optimization, are comparable with high-electronic-quality CH4-based samples at the same optical gap. The network structure of C2H2 based films differs from CH4 based films, as revealed by infrared spectroscopy.