Optical properties and local bonding configurations of hydrogenated amorphous silicon nitride thin films

We report on the optical properties and local bonding configurations of both as-deposited and postannealed hydrogenated amorphous silicon nitride (a-SiNx:H) thin films grown on crystalline Si substrates with x approximately 1.2 +/- 0.1. Ultraviolet optical reflection and infrared (IR) absorption measurements were applied to characterize the films. A method simply based on optical reflection spectra is proposed for accurate determination of the optical band gap, band tail, wavelength-dependent refractive index and extinction coefficient, as well as the film thickness, suggesting that the Tauc-Lorentz [G. E. Jellison, Jr. and F. A. Modine, Appl. Phys. Lett. 69, 371 (1996); 69, 2137 (1996)] model with the inclusion of Urbach tail is the optimal one to describe the optical response of a-SiNx:H films. The yielded optical parameters can be related well to the film microstructure as revealed by the IR absorption analysis. These results have implications for future deposition controlling and device applications. (c) 2006 American Institute of Physics.