Si 1− xC x formation by reaction of Si(111) with acetylene: growth mode, electronic structure and luminescence investigation

Abstract

The carbonization process of a Si(111) 7×7 reconstructed surface exposed to acetylene (C 2H 2) has been investigated by combining several structural, electronic, and luminescence techniques. The aim was to give a comprehensive scenario of the different carbonaceous phases formed on the clean silicon surface starting from the C 2H 2 molecule chemisorbed at room temperature up to the formation of a crystalline c-SiC compound. We found that the molecule breaks at about 450°C and for temperatures up to 600°C a Si 1− x C x alloy is formed inside the sample. For higher temperatures, up to 850°C, c-SiC crystallite precipitation epitaxially grown on the Si surface is observed. The near-edge-energy loss spectra at the carbon K edge ensures that for C 2H 2 deposition temperatures higher than 600°C the carbon bonds are sp 3-like, thus demonstrating the absence of non-substitutional carbon concentration. The luminescence spectra performed at each stage of carbonization revealed the formation of well-defined Si 1− x C x phases (with x of a few percent) and clearly demonstrate that the exposure to C 2H 2 is a highly efficient method to change in a continuous way the near-infrared optical properties of silicon surfaces in the spectral range from 0.9 to 1.1 eV.