The effect of hydrogen dilution on the optical properties of a wide band gap amorphous semiconductor (a-Si:C:H) was investigated. The samples were prepared by glow discharge decomposition of tetramethylsilane and were characterized primarily by optical techniques: spectroscopic ellipsometry, Raman scattering, infrared absorption, spectrophotometry, and UV photoluminescence. The deposition rate decreased with hydrogen dilution, while the silicon to carbon ratio remained constant with the addition of hydrogen. The optical band gap of this material increased as the hydrogen flow rate increased. Infrared absorption studies show that the concentration of hydrogen which is bonded to carbon decreases systematically upon hydrogen dilution. Hydrogen dilution appears to reduce the size and concentration of sp2 bonded carbon clusters, possibly caused by the etching of sp2 clusters by atomic hydrogen. The result was also supported by the shift of the Raman G peak position to a lower wave number region. Room temperature photoluminescence in the visible spectrum was observed with UV excitation.

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The UCD community has made this article openly available. Please share how this access benefits you. Your story matters! (@ucd_oa) Some rights reserved. For more information, please see the item record link above. This study presents results of wavelength-dependent Raman scattering from amorphous silicon carbon (a-Si:C:H). The a-Si:C:H films were produced by radio-frequency plasma-enhanced chemical vapor deposition. Prior results with amorphous carbon indicate that laser excitation selectively probes clusters with differing sizes. Our measurements with a-Si:C:H indicate that when using red (632.8 nm), green (514.5 nm), and blue (488.0 nm) excitation, the Raman D and G peaks shift to higher wave numbers as the excitation energy increases. The higher frequency is associated with smaller clusters that are preferentially excited with higher photon energy. It appears that photoluminescence occurs due to radiative recombination from intracluster transitions in Si-alloyed sp 2 -bonded carbon clusters.