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The authors 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 gap then the localized states extend over large clusters 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.

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Atomic-scale structure changes in gallium lanthanum sulphide bulk glass and ablation-deposited thin films have been studied by the x-ray absorption fine-structure (EXAFS) technique. EXAFS spectra have been recorded at the sulphur and gallium K edges, and the lanthanum edge, and this has allowed us to construct a detailed picture of the local structure in bulk glass and thin films. The EXAFS results indicate that there is chemical disorder in the structural network of the GLS thin films, although chemical ordering is predominant in bulk GLS glass. The existence of `wrong bonds', i.e. Ga - Ga and S - S bonds, in the structure has been discussed and correlated with optical absorption experiments undertaken on the same samples to provide a consistent picture of the local structure.