Columnar growth of ultra-thin nanocrystalline Si films on quartz by Low Pressure Chemical Vapor Deposition: accurate control of vertical size

Ultra-thin nanocrystalline silicon films with varying thickness from 5 to 30nm were grown on quartz by low pressure chemical vapor deposition (LPCVD) of Si. Observations on cross-sectional transmission electron microscopy (TEM) specimens revealed that the films had a columnar growth, i.e. the third dimension of the nanocrystals, perpendicular to the Su/SiO2 interface, was approximately equal to the film thickness, while the lateral size of nanocrystals was defined during the initial stage of growth and was not very much affected by the film thickness. The observed columnar growth gives the possibility to obtain two-dimensional nanocrystal arrays on quartz with well defined size in the z-direction. Plane view images showed that the lateral distribution of nanocrystal size presents a well-defined maximum in all the films. The mean lateral size of the nanocrystals did not change very much with the film thickness, being in the range of 11-13 nm. The number of grains with size larger than the mean one tended to increase with the thickness of the film. (C) 2008 WILEY-VCH Veriag GmbH & Co. KGaA, Weinheim