MAGNETORESISTANCE AND HALL-EFFECT IN AMORPHOUS SILICON-TANTALUM ALLOYS NEAR THE METAL-INSULATOR-TRANSITION

Magnetoresistance (NIR) and Hall effect (HE) measurements in hydrogena ted (H) and unhydrogenated (UH) samples of silicon-tantalum alloys wit h compositions situated on both sides of and near the metal-insulator transition (MIT) are presented. The measurements at room temperature o n 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 gr eater than the metallic samples. For the measurements at low temperatu res (4.2 and 1.7 K, respectively) on some metallic samples the MR was positive, and larger at the lower temperature. HE measurements have sh own positive carriers. From these measurements the density of carriers and the Hall mobility have been evaluated. The Si-Ta system is discus sed in comparison with the Si-Ni system. Based on the obtained results a model of the band structure is proposed, which explains the anomalo us HE seen in amorphous metal-semiconductor systems. (C) 1998 Elsevier Science B.V. All rights reserved.