Microstructure and dynamics of hydrogen in a-Si:H detected by nuclear magnetic resonance

A proton nuclear magnetic resonance (NMR) study of a-Si:H was carried out on both hydrogen-diluted and nonhydrogen-diluted device quality glow-discharge (GD) a-Si:H films. The main features of the proton spectrum are the previously reported line with a linewidth of a few kHz and a line with a linewidth > 25 kHz. However, the broader line is a superposition of two peaks, rather than a single peak. Spin-lattice relaxation time (T-1) measurements of the non-H-diluted a-Si:H indicate that the spectral component with the greatest width (approximate to 80 kHz) relaxes about four times faster than the approximate to 35 kHz and the few kHz peaks. T-1 measurements cannot resolve components of the H-diluted a-Si:H spectrum and in that case the deviation from a single Gaussian function fitted to the approximate to 35 kHz line is much less. Above room temperature the intensity of the broadest line decreases whereas the narrow peak and a narrower portion of the broad peak increase in intensity. These spectral changes are reversible at temperatures < 200 degrees C. The temperature dependence of the spectra is larger for the non-H-diluted sample. We speculate that the temperature dependence is related to the intensity of the broadest spectral component and that this component may be associated with isolated trapped molecular hydrogen. (C) 2000 Elsevier Science B.V. All rights reserved.