Nuclear-magnetic-double-resonance investigation of the dopant microstructure in hydrogenated amorphous silicon

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Abstract
Information on the local environment of dopants in compensated and singly doped amorphous Si has been obtained using NMR spin-echo double-resonance spectroscopy, a technique that is very sensitive to interatomic distance. It is found that there is a nonrandom local configuration around the dopants in these materials. In the compensated samples, almost half of the boron atoms have a phosphorus atom in the first-neighbor shell. This is higher than the value for a random distribution and indicates that there is significant clustering of the dopants in compensated material. In addition, the hydrogen atom is not directly bonded to either of these dopants. For the singly doped materials, the H-dopant structure is similar to that of the compensated samples for the P-doped samples but different for the B-doped material. For these, almost half of the B atoms have a hydrogen atom in the first-neighbor shell. This is to be contrasted with the P-doped samples where the H atoms are in second- or further-neighbor shells. Aspects of this local structure of P and B in hydrogenated amorphous Si are similar to those proposed for the dopant-H structures in hydrogen-passivated crystalline Si.