Preparation Of Hydrogenated Amorphous-Silicon With Tunable Gap By Homogeneous Chemical Vapor-Deposition

This paper reports on the properties of doped and undoped amorphous silicon films deposited by the homogeneous chemical vapor deposition (HOMOCVD) technique. It is shown that good quality films can be grown at reasonable deposition rates of 100–150 Å/min. It is also shown that in this growth regime, the main precursor is Si2H4, shifting to SiH2 at higher H2 dilution. The real limit for the growth rate is set by the phenomena of homogeneous and local nucleation. The optical band gap of undoped films deposited at these high growth rates, changes from 2.6 eV for a substrate temperature of 20 °C down to 1.6 eV at 280 °C. Very conductive B-doped HOMOCVD amorphous silicon films with tunable band gap can be obtained. This is very important for the use of such films for window layers in photovoltaic applications as an alternative to siliconcarbide. At a substrate temperature of 40 °C films were obtained with an optical gap of 2.34 eV and a room-temperature dark conductivity of 1.6×10−5/Ω cm. Down to a thickness of 100 Å, no thickness dependence of the dark conductivity has been observed.