Thin Solid Films, Vol.518, No.23, 6818-6828, 2010
High band gap nanocrystallite embedded amorphous silicon prepared by hotwire chemical vapour deposition
Hydrogenated silicon films ranging from pure amorphous to biphasic i.e., nanocrystallites embedded amorphous silicon are prepared in an indigenously fabricated hot wire chemical vapor deposition chamber by varying the substrate temperature (Ts) and process pressure (PP). The deposition rates are found to be about 2.5-14 A/s, which is very much appreciated for the fabrication of cost effective devices. While the films deposited at low T(s) are amorphous in nature, those deposited at T(s)>= 200 degrees C contain nanocrystallites embedded in the amorphous network These mixed phase films show high crystalline fraction of 50-56%. All the films deposited at 250 degrees C, by varying PP, are nanocrystallite embedded with crystalline fraction 60-75%. The optical band gaps of the films (2.0-2.37 eV) are high compared to the regular films, whereas the hydrogen content remains in the reported range of 2.5-5 at.%. We attribute the high optical band gap to the improved order as well as the presence of low density amorphous tissues surrounding the grain boundary regions. The ease of depositing films with tunable band gap is useful for fabrication of tandem solar cells. (C) 2010 Elsevier B.V. All rights reserved.