Magnetron sputtering synthesis of silicon-carbon films:: Structural and optical characterization

This study deals with the growth control and characterization of wide band gap silicon-carbon films obtained by reactive hydrogen plasma sputtering. The films were grown in a pure hydrogen plasma with different values of the carbon-to-silicon sputtered area ratio, r(C). During deposition, the substrate temperature was maintained at 730 degrees C. Infrared absorption, Raman scattering and X-ray photoelectron spectroscopy, in addition to optical absorption, were used for the investigations. For C-poor samples (r(C)less than or equal to 30%), Si nanocrystals were formed, together with a small fraction of amorphous SiC. Further increase of sputtered carbon (R(C)greater than or equal to 35%) led to a drastic change, resulting in SiC crystallization at the expense of Si and a near-stoichiometric composition of the layers (C/Si atomic ratio of similar to 1.04). Excess carbon in the lavers segregates in graphitic-like configuration. being likely located in the intergrain regions. The abrupt structural change observed for 30% less than or equal to r(C)less than or equal to 35% is accompanied by a consistent widening of the optical band gap. This is observed by a significant blue shift of the optical absorption towards the values reported for single crystal SiC. The energy gap at which optical absorption is 5 x 10(4) cm(-1) shifts from 2.2-2.3 eV to about 4.1 eV. This structural change also correlates with a significant decrease of the refractive index. (C) 1998 Published by Elsevier Science Ltd. All rights reserved.