Amorphous silicon films and solar cells deposited by HWCVD at ultra-high deposition rates

The deposition conditions for hydrogenated amorphous silicon. deposited by hot wire chemical vapor deposition, are linked to the film structure as we increase deposition rates (R-d) to >100 Angstrom/s. At low R-d (<20 Angstrom/s). films with optimal properties are deposited under low silane depletion conditions. and all measures of structure (X-ray diffraction. Raman spectroscopy. H evolution. small-angle X-ray scattering (SAXS)) indicate a compact material. At high R-d (>100 Angstrom/s). optimum films are deposited under silane depletion conditions as high as 75-80%. and all structural properties except for the SAXS results once again indicate a compact material, We relate changes in the film electronic structure (Urbach edge) with increasing R-d to the increase in the SAXS signals. and note the invariance of the saturated defect density versus R-d, discussing reasons why these microvoids do not play a role in the Staebler-Wronski effect for these films. Finally, we present device results over the whole range of R-d that we have studied and suggest why. at high R-d, device quality films can be deposited at such high silane depletions. (C) 2002 Published by Elsevier Science B.V.