Amorphous silicon-carbon hydrogen alloy was prepared by radio frequency glow discharge decomposition of a silane-methane mixture. The infrared absorption spectra were measured at various stages of thermal annealing. By observing the change of relative intensities between these peaks the hydrogen bonding responsible for the absorption peaks could be assigned more accurately, for example, the stretching mode of monohydride Si–H is determined by its local environment, which supports H. Wagner’s and W. Beyer’s results [Solid State Commun. 48, 585 (1983)] but is inconsistent with the commonly believed view. It is also found that a significant fraction of carbon atoms are introduced into the film in –CH3 configuration which forms a local void and enhances the formation of polysilane chain and dangling bond defects. Only after high-temperature annealing are the hydrogen atoms driven out, and Si and C start to form a better silicon carbide network.
The physical and electronic structure of hydrogenated amorphous silicon carbide (a-SiC:H) are identified by measuring its photoluminescence and infrared spectra at various stages of thermal annealing. It is found that Brodsky’s [Solid State Commun. 36, 55 (1980)] quantum well model can be successfully applied to explain the observed results, such as the double peak structure in photoluminescence spectrum and the physical origin of the optical gap widening due to carbon incorporation.
Amorphous silicon-carbon hydrogen alloy was prepared by radio frequency glow discharge decomposition of silane-ethylene mixture. The infrared absorption spectra were measured at various stages of thermal annealing. By observing the change of relative intensities between these peaks the molecular bonding responsible for the absorption peaks could be assigned. For example, in addition to the CH3 radical commonly found in films prepared by silane-methane mixture, other carbon hydrogen radicals such as CH2 and C2H5 were also unambiguously identified. At same gas phase flow ratio (Xg = 0.8), the CHx contents of ethylene-based film is about 6.6 times larger than that of the methane-based film. Hence, to grow a-SiC:H with a larger optical gap, the ethylene will be a good choice as the deposition source.
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