Amorphous and microcrystalline silicon films grown at low temperatures by radio-frequency and hot-wire chemical vapor deposition

The effect of hydrogen dilution on the optical, transport, and structural p roperties of amorphous and microcrystalline silicon thin films deposited by hot-wire (HW) chemical vapor deposition and radio-frequency (rf) plasma-en hanced chemical vapor deposition using substrate temperatures (T-sub) of 10 0 and 25 degrees C is reported. Microcrystalline silicon (mu c-Si:H) is obt ained using HW with a large crystalline fraction and a crystallite size of similar to 30 nm for hydrogen dilutions above 85% independently of T-sub. T he deposition of mu c-Si:H by rf, with a crystallite size of similar to 8 n m, requires increasing the hydrogen dilution and shows decreasing crystalli ne fraction as T-sub is decreased. The photoconductivity, defect density, a nd structure factor of the amorphous silicon films (a-Si:H) are strongly im proved by the use of hydrogen dilution in the T-sub range studied. a-Si:H f ilms with a photoconductivity-to-dark conductivity ratio above 10(5), a dee p defect density below 10(17) cm(-3), an Urbach energy below 60 meV and a s tructure factor below 0.1 were obtained for rf films down to 25 degrees C ( at growth rates similar to 0.1-0.4 Angstrom/s) and for HW films down to 100 degrees C (at growth rates similar to 10 A/s), using the appropriate hydro gen dilution. In the low T-sub range studied, the growth mechanism, film pr operties, and the amorphous to microcrystalline silicon transition depend o n the flux of atomic hydrogen available. The properties of the films are co mpared to those of samples produced at 175 and 250 degrees C in the same re actors. (C) 1999 American Institute of Physics. [S0021-8979(99)04219-X].