New Hydrogen Distribution ina-Si:H: An NMR Study

Hot-filament-assisted CVD deposited a-Si:H with low H concentration and low defect density has been examined by ${}^{1}$H NMR. It is demonstrated for the first time that H microstructures can be altered significantly in device quality a-Si:H films. In the present films, large H clusters account for 90% of the 2--3 at. % H atoms, with the remaining H more dispersed, but still aggregated in a small volume fraction of the material. These results suggest that an ideal a-Si:H network with low defect density and high structural stability may not necessarily be homogeneous.