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

Hydrogenated amorphous silicon, alpha-Si:H, is deposited from silane and hydrogen by hot-wire chemical vapor deposition using a tungsten wire filament at a temperature T-fil = 1200 degrees C. Film properties depend on whether the films were deposited using filaments with an accumulated deposition time lower than 90 min (''new'' filaments) or longer than 90 min (''old'' filaments), The deposition rate for films deposited with ''new'' filaments is 4 times higher than that for aged filaments. 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 controlled by the substrate temperature T-sub, and show different dependences for ''new'' and ''old'' filaments, The Urbach band tail energy, E(u), is lower for films deposited with ''new'' filaments. A kinetic growth model for hot-wire chemical vapor deposition in the T-fil similar to 1200 degrees C regime is proposed. (C) 1995 American Institute of Physics.