Si1-xCx formation by reaction of Si(111) with acetylene: growth mode, electronic structure and luminescence investigation

The carbonization process of a Si(111) 7 x 7 reconstructed surface exposed to acetylene (C2H2) has been investigated by combining several structural, electronic, and luminescence techniques. The aim was to give a comprehensiv e scenario of the different carbonaceous phases formed on the clean silicon surface starting from the C2H2 molecule chemisorbed at room temperature up to the formation of a crystalline c-SiC compound. We found that the molecu le breaks at about 450 degrees C and for temperatures up to 600 degrees C a Si1-xCx alloy is formed inside the sample. For higher temperatures, up to 850 degrees C, c-SiC crystallite precipitati on epitaxially grown on the Si surface is observed. The near-edge-energy lo ss spectra at the carbon K edge ensures that for C2H2 deposition temperatur es higher than 600 degrees C the carbon bonds are sp(3)-like, thus demonstr ating the absence of non-substitutional carbon concentration. The luminesce nce spectra performed at each stage of carbonization revealed the formation of well-defined Si1-xCx phases (with x of a few percent) and clearly demon strate that the exposure to C2H2 is a highly efficient method to change in a continuous way the near-infrared optical properties of silicon surfaces i n the spectral range from 0.9 to 1.1 eV. (C) 1999 Elsevier Science B.V. All rights reserved.