Device-quality polycrystalline silicon films deposited at low process temperatures by hot-wire chemical vapor deposition

Device-grade undoped hydrogenated polycrystalline silicon thin films have b een developed from a gas mixture of silane and hydrogen using a her-wire ch emical vapor deposition (HW-CVD) method. optimizing the deposition paramete rs. Proper design of the HW-CVD reactor helps to deposit a uniform quality of film over a large area (100 cm(2)) with a two filament configuration. Ex tensive studies have been made of the effects of hydrogen dilution (4-60), substrate temperature (180-400 degrees C) and filament temperature (1500-17 00 degrees C) on the film growth. Atomic force micrographs give a quantitat ive estimate of roughness for these films. UV-visible ellipsometry analyses confirm their compactness and crystallinity while X-ray diffraction patter ns allow for the determination of the crystallite sizes (up to 300 Angstrom ). Using a hydrogen dilution of 60, a substrate temperature of 300 degrees C and a filament temperature of 1500 degrees C, a dark conductivity of 2.5 x 10(-5) S/cm and its activation energy of 0.45 eV have been obtained. For these films, the Hall mobility attains 10 cm(2)/V s. With these deposition parameters, the intrinsic layer of complete p-i-n HW-CVD solar cells has be en realized. These cells, deposited on TCO coated Coming glass substrates, exhibit 1.8% conversion efficiency under 100 mW/cm(2) irradiation. (C) 1999 Published by Elsevier Science S.A. All rights reserved.