STRUCTURAL AND OPTICAL-PROPERTIES OF HYDROGENATED AMORPHOUS-SILICON CARBIDE DEPOSITED BY GLOW-DISCHARGE FROM C3H8-SIH4-H2 MIXTURE

Films of hydrogenated amorphous silicon carbide (a-SiC:H) have been prepared by a glow discharge decomposition from ps mixtures Of C3H8-SiH4-H2 and CH4-SiH4-H2, in order to examine the effect of hydrocarbon gases on the structural and optical properties of these films. To study the influence of hydrogen on those properties of the propane-based films, the properties of the films deposited at different substrate temperatures (T(s)) are systematically investigated using infrared (IR) and ultraviolet-visible absorption spectroscopies. By observing the change of intensities of IR absorption peaks with substrate temperature, the hydrogen bonding responsible for the absorption peaks could be assigned more accurately. When T(s) is increased up to 300-degrees-C, intensities of CH3 and SiH2 groups are reduced, indicating the formation of a dense network structure. At the same carbon concentration in ps mixtures, propane allows more carbon and hydrogen atoms to be effectively incorporated into the film than methane. The IR spectra reveal that the structure of a propane-based film has the characteristics of that of two kinds of films, methane- and ethylene-based films. It is found that the chemical bonding nature of the hydrocarbon ps strongly affects the bonding structure and the composition of the films. From these results, it is proposed that the use of propane is suitable for the fabrication of high-quality a-SiC:H with a wide optical gap ( > 2.0 eV) and a deposition rate of approximately 2 angstrom/s.