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

Abstract

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= [SiH 4]/[H 2] between 10% and 9%, where [SiH 4] and [H 2] are the silane and hydrogen flow rates, by Raman and optical absorption spectra, and by dark conductivities which are several orders of magnitude larger in microcrystalline as compared to amorphous films. In the microcrystalline films we observe a simultaneous increase of both majority and minority carrier mobility-lifetime products with increasing hydrogen dilution, which is consistent with the measured decrease in sub-gap absorption and defect density deduced from transient photocurrent measurements. This simultaneous increase is in contrast with the general trend observed in amorphous films, where these two quantities vary in opposite ways, and are associated with an improvement of the transport properties of the material. The microcrystalline samples did not show light-induced degradation after prolonged illumination.