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 effec t 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 conductivi ty of 8.2 x 10(-9) S cm-1 along with low optical absorption. The bonde d hydrogen content in the film is 6 at.% as estimated from IR spectra. X-ray and electron diffraction study revealed the film to be microcry stalline. 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 51 8 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 th e crystallites. However, the optical absorption of the film is lower t han that of muc-Si:H as the absorption is governed by the amorphous pa rt.