Incorporation of sulfur into hydrogenated amorphous carbon films

Amorphous hydrogenated carbon-sulfur thin films (a-C:H:S) were deposited from CH4/H2S gas mixtures by capacitively-coupled radio-frequency PECVD. X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) were used to probe the composition of the films. XPS showed that the sulfur atomic percentage within a film was proportional to the fraction of H,S in the H2S/CH4 gas mixture, and that films had been deposited with a sulfur content of up to 27 at.%. SIMS showed that the distribution of C and S was homogeneous throughout the films. Ex situ variable angle spectroscopic ellipsometry was used to evaluate the band gap energy variation by three different methods. Values of the E04 band gap for these films were between 1.5 and 2.5 eV, with refractive index values of between 1.8 and 2.1. Laser Raman spectroscopy (514.5 nm) suggested that the addition of sulfur increases the clustering of aromatic six-membered rings. (C) 2003 Elsevier B.V. All rights reserved.