LOW FILAMENT TEMPERATURE DEPOSITION OF A-SI-H BY HOT-WIRE CHEMICAL-VAPOR-DEPOSITION

Hydrogenated amorphous silicon, alpha-Si:H, is deposited from silane a nd hydrogen by hot-wire chemical vapor deposition using a tungsten wir e filament at a temperature T-fil = 1200 degrees C. Film properties de pend on whether the films were deposited using filaments with an accum ulated deposition time lower than 90 min (''new'' filaments) or longer than 90 min (''old'' filaments), The deposition rate for films deposi ted with ''new'' filaments is 4 times higher than that for aged filame nts. For ''new'' filaments, a monotonic increase of the growth rate, r (d), with the pressure is observed, as well as a maximum of r(d) for F -H2/F-SiH4 close to unity. The optoelectronic properties are controlle d by the substrate temperature T-sub, and show different dependences f or ''new'' and ''old'' filaments, The Urbach band tail energy, E(u), i s lower for films deposited with ''new'' filaments. A kinetic growth m odel for hot-wire chemical vapor deposition in the T-fil similar to 12 00 degrees C regime is proposed. (C) 1995 American Institute of Physic s.