Magnetoresistance and Hall effect in amorphous silicon-tantalum alloys near the metal-insulator transition

Magnetoresistance (NIR) and Hall effect (HE) measurements in hydrogenated (H) and unhydrogenated (UH) samples of silicon-tantalum alloys with compositions situated on both sides of and near the metal-insulator transition (MIT) are presented. The measurements at room temperature on both H and UH samples have shown a small positive MR of about 0.003 at B =1 T. The insulating samples gave a negative MR about 10 times greater than the metallic samples. For the measurements at low temperatures (4.2 and 1.7 K, respectively) on some metallic samples the MR was positive, and larger at the lower temperature. HE measurements have shown positive carriers. From these measurements the density of carriers and the Hall mobility have been evaluated. The Si-Ta system is discussed in comparison with the Si-Ni system. Based on the obtained results a model of the band structure is proposed, which explains the anomalous HE seen in amorphous metal-semiconductor systems. (C) 1998 Elsevier Science B.V. All rights reserved.