Conduction in n+-i-n+ thin-film polycrystalline/silicon devices in relation to the film deposition conditions

The electrical conduction in n+-i-n+ thin-film polycrystalline/silicon devices, in relation to the deposition conditions of the low-pressure chemically vapor deposited film, is investigated. Transmission electron microscopy study showed the following: (i) By decreasing the growth pressure from 180 to 80 mTorr, the mean grain size increases by a factor of 3. (ii) In the material grown at 180 mTorr, there is a mean dilatation for the d111 lattice plane amounting to 2.7%, while in the material grown at 80 mTorr, the systematic dilatation previously observed is absent. The current-voltage characteristics show a linear behavior in a voltage region and a nonlinear behavior at higher voltages attributed to Joule heating within the sample. The energy gap of the material grown at 80 mTorr is 1.12 eV, while for the material grown at 180 mTorr, it decreases to 0.96 eV. The shrinkage of the energy gap could be due to the high density of ‘‘tail states’’ close to the conduction or valence band.