Electronic properties of silicon thin films prepared by hot-wire chemical vapour deposition

A transition from amorphous to microcrystalline silicon occurs in hot-wire chemical vapour deposition silicon films with increasing dilution of silane with hydrogen. This transition is detected for a dilution ratio R = [SiH4] /[H-2] between 10% and 9%, where [SiH4] and [H-2] are the silane and hydrog en flow rates, by Raman and optical absorption spectra, and by dark conduct ivities which are several orders of magnitude larger in microcrystalline as compared to amorphous films. In the microcrystalline films we observe a si multaneous increase of both majority and minority carrier mobility-lifetime products with increasing hydrogen dilution, which is consistent with the m easured decrease in sub-gap absorption and defect density deduced from tran sient photocurrent measurements. This simultaneous increase is in contrast with the general trend observed in amorphous films, where these two quantit ies vary in opposite ways, and are associated with an improvement of the tr ansport properties of the material. The microcrystalline samples did not sh ow light-induced degradation after prolonged illumination. (C) 2000 Elsevie r Science B.V. All rights reserved.