POLYCRYSTALLINE SILICON FILMS OBTAINED BY HOT-WIRE CHEMICAL-VAPOR-DEPOSITION

Silicon films were deposited at moderate substrate temperatures (280-5 00 degrees C) from pure silane and a silane-hydrogen mixture (10% SiH4 , 90% H-2) in a hot-wire CVD reactor. The morphology, structure and co mposition of the samples were studied with scanning electron microscop y, transmission electron microscopy, transmission electron diffraction , X-ray diffraction, Raman spectroscopy and secondary ion mass spectro metry. The sample deposited at 500 degrees C with pure silane has an a morphous structure, whereas the samples obtained from silane diluted i n hydrogen have a polycrystalline structure, even that grown at the lo west temperature (280 degrees C). Polycrystalline samples have a colum nar structure with 0.3-1 mu m crystallite sizes with preferential orie ntation in [220] direction. Deposition rates depend on the filament-su bstrate distance and range from 9.5 to 37 Angstrom/s for the polycryst alline samples. The high quality of the polycrystalline samples obtain ed makes the hot-wire technique very promising. Moreover, it is expect ed to be easily scaled up for applications to large-area optoelectroni c devices and to photovoltaic solar cells.