Raman study of thin films of amorphous-to-microcrystalline silicon prepared by hot-wire chemical vapor deposition

Abstract

The structure changes of thin films of amorphous (a) to microcrystalline (μc) silicon are studied by Raman scattering in terms of three deposition parameters: the silane flow rate, the hydrogen flow rate, and the total gas pressure in hot-wire chemical vapor deposition. The Raman transverse optical (TO) mode is deconvoluted into two Gaussian functions for a-Si:H and intermediate components and one Lorenzian function for the c-Si component. We found that (a) in general, the change in structure is a function of the ratio of hydrogen to silane gas flow, R, but also depends on the SiH4 flow rate and total gas pressure; (b) there is a narrow structural transition region in which the short-range order of the a-Si:H network improves, i.e., the variation in bond angle of the a-Si network decreases from ∼10° to ∼8° once the c-Si grains start to grow; and (c) when the films were deposited using a high SiH4 flow rate of 22 sccm, the narrow TO mode with low peak frequency could be related to the column-like structures.