Magnetron sputtering synthesis of silicon–carbon films: structural and optical characterization

Abstract

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°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≤30%), Si nanocrystals were formed, together with a small fraction of amorphous SiC. Further increase of sputtered carbon ( r C≥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 ∼1.04). Excess carbon in the layers segregates in graphitic-like configuration, being likely located in the intergrain regions. The abrupt structural change observed for 30%≤ r C≤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 5×10 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.