MICROCRYSTALLINE SILICON-CARBON ALLOY FILM PREPARED BY PHOTOCHEMICAL VAPOR-DEPOSITION

Silicon carbon alloy thin films were prepared by photo-chemical vapour deposition using SiH4 and C2H2 gases, diluted with 97% H-2. The effect of chamber pressure on the properties of the film were investigated and are explained from the standpoint of growth mechanism. The 0.4 mum thin film prepared at a pressure of 67 Pa exhibited a dark conductivity of 8.2 x 10(-9) S cm-1 along with low optical absorption. The bonded hydrogen content in the film is 6 at.% as estimated from IR spectra. X-ray and electron diffraction study revealed the film to be microcrystalline. The observed crystalline planes are ascribed to crystalline silicon (c-Si), embedded in amorphous silicon carbon (a-SiC:H) tissue. This is also confirmed by the appearance of the TO mode of c-Si at 518 cm-1 in the Raman spectrum. Thus in microcrystalline silicon carbon (muc-SiC) film, the crystallinity is due to silicon alone while carbon is present at grain boundaries and in amorphous regions separating the crystallites. However, the optical absorption of the film is lower than that of muc-Si:H as the absorption is governed by the amorphous part.