CONDUCTIVITY AND MAGNETORESISTANCE OF HYDROGENATED AMORPHOUS-SILICON NICKEL-ALLOYS NEAR THE METAL-INSULATOR-TRANSITION

We present conductivity and magnetoresistance data for a range of a-Si1-yNiy:H alloys near the metal-insulator transition. In the metallic regime, weak-localization and interaction effects are identified, the latter being of normal sign. In the activated regime, conductivity results imply variable-range hopping in a parabolic density of states, but quantitative analysis shows that if this density of states results from a Coulomb pp, then the localized states extend over large dusters of nickel atoms. The magnetoresistance data generally show positive magnetoresistance attributed to spin splitting in interaction effects, but negative magnetoresistance, attributed to suppression of weak-localization-type interference, is seen on the insulating side of the transition at not too low temperatures where interaction effects are partially suppressed.