Silicon nanocrystals on amorphous silicon carbide alloy thin films: Control of film properties and nanocrystals growth

摘要

The present study demonstrates the growth of silicon nanocrystals on amorphous silicon carbide alloy thin films. Amorphous silicon carbide films [a-Si_(1-x)C_x:H (with x<0.3)J were obtained by plasma enhanced chemical vapor deposition from a mixture of silane and methane diluted in hydrogen. The effect of varying the precursor gas-flow ratio on the film properties was investigated. In particular, a wide optical band gap (2.3 eV) was reached by using a high methane-to-silane flow ratio during the deposition of the a-S_(1-x)C_x:H layer. The effect of short-time annealing at 700 ℃ on the composition and properties of the layer was studied by X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was observed that the silicon-to-carbon ratio in the layer remains unchanged after short-time annealing, but the reorganization of the film due to a large dehydrogenation leads to a higher density of SiC bonds. Moreover, the film remains amorphous after the performed short-time annealing. In a second part, it was shown that a high density (1×10~(12)cm~(-2)) of silicon nanocrystals can be grown by low pressure chemical vapor deposition on a-Si_(0.8)C_(0.2) surfaces at 700 ℃, from silane diluted in hydrogen. The influence of growth time and silane partial pressure on nanocrystals size and density was studied. It was also found that amorphous silicon carbide surfaces enhance silicon nanocrystal nucleation with respect to SiO_2, due to the differences in surface chemical properties.