Structural study of hydrogenated amorphous silicon–carbon alloys

Abstract

The structure of amorphous alloy films of a-Si_1−xC_x: H has been investigated as a function of x using energy-filtered electron diffraction. The films were prepared by d.c. magnetron plasma deposition from mixtures of silane and methane. Electron-energy-loss spectroscopy was used to determine film composition and to measure the plasmon frequency as a function of x. A film of a-Sic prepared by vacuum evaporation was also studied. For plasma-deposited films with x < 0·5, the radial distribution function shows peaks corresponding to C-C, Si-C and Si-Si bonding and also shows that carbon substitutes for silicon in a random tetrahedral network with some carbon-carbon bonding. For x > 0·5 the radial distribution function shows major peaks corresponding to C-C and Si-C bonding, with no observable Si-Si bonding. The presence of regions rich in carbon is inferred from this and from the plasmon results. For x = 1 the films show a structure in which the degree of fourfold bonding increases with substrate temperature. The a-Sic film shows only silicon-carbon bonding, in agreement with published work.