Mechanisms for peculiar low-temperature phenomena in hydrogenated amorphous silicon

Concepts based on Si H bond breakup (normal strength 3.5 eV) or weakly bonded H have not accounted satisfactorily for many low-temperature phenomena: rapid decrease in the spin signal in the range 25 300?deC while the Si H bond density is conserved or decreases; early H evolution stage at 200 50?deC and H diffuision, both with an activation energy of only 1.5 eV, etc. An elegant microscopic explanation of these and other phenomena is given in terms of a novel mechanism that is unique to the amorphous state: defect-mediated H diffusion during which the defects are annihilated. © 1987 The American Physical Society.