LOCAL-STRUCTURE AND BONDING STATES IN A-SI1-XCX-H

Infrared spectra of a-Si1-xCx:H deposited in a glow discharge of a sil ane/methane mixture have been measured. Comparison with elastic recoil detection and Rutherford backscattering spectrometry shows that the m ean number of hydrogen atoms attached to silicon per silicon atom ([H( Si)]/[Si]) increases with higher carbon content and that more Si-H-2 b onding configurations are formed. Hydrogen is preferentially bonded in (Si-H-2)n clusters, which partly explains the observed apparent shift of the Si-H stretching mode to higher energy. The remaining contribut ion to this shift is believed to result from Si-H on surfaces of voids instead of an inductive effect. From composition measurements we obse rve that for each carbon atom, three hydrogen atoms are incorporated i n the material, suggesting that during deposition carbon is initially incorporated in CH3 groups. However, the mean number of C-H bonds per carbon atom decreases from about 2.2+/-0.4 to 1.4+/-0.3 with increasin g carbon content, indicating that the majority of the carbon atoms is two- or threefold coordinated to silicon.