Characterization of the protonic distribution and environment in amorphous silicon-hydrogen alloys using proton NMR and ESR

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Abstract
We present magnetic resonance data from a series of a‐Si(H) samples deposited under varied hydrogen partial pressures. This parameter has been shown to be directly related to the sample‐wide average proton density. The other sputtering parameters were maintained such that no dihydride bonding (as determined by the 890 cm−1ir bending mode) is present. Measurements presented are the NMR absorption spectrum (from the Fourier transform of the free induction decay), relaxation time T1, and ESR absorption. The NMR absorption spectrum identifies two distinct forms of H incorporation. One is a tightly clustered form, such as H bonded on the inner surface of a microvoid of maximum dimension 5?, while the other is a randomly distributed phase with local H density of 3.5×1021 cm−3. The distributed phase H density is independent of the sample‐wide average, indicating a fixed composition phase which occupies a larger percentage of the sample as H pressure is increased during deposition. This phase appears to extend to a maximum of 88% of the sample. The protonic spin‐lattice relaxation time (T1) measures the coupling of the spin system to its enviroment, ’’the lattice’’. For the series of samples, we find that T1 first increases from 2.8 s to 44.8 s with increasing H content and then decreases to 8.1 s as H density is further increased. In an effort to understand this unusual relaxation behavior, we have made temperature dependant T1 and ESR measurements. Utilizing these results, the protonic relaxation mechanism is discussed in terms ’’disorder mode’’ and electronic state models.

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