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 non-hydrogen-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 ( 80 kHz) relaxes about four times faster than the 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 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°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.