Galvanomagnetic Effects in p-Type Tellurium at Low Temperatures. III. – Impurity Band Conduction and Negative Magneto-resistance in Sb-Doped Crystals –

Galvanomagnetic effects of Sb-doped tellurium were investigated in the wide temperature range from 77 K to 0.05 K under the magnetic fields up to 18 kOe. The hole concentrations of the samples were ranging from 4.2×10 15 cm -3 to 1.5×10 16 cm -3 . Temperature dependences of the conductivity and the weak field Hall coefficient of the samples with holes of 4.2∼7.2×10 15 cm -3 indicated the occurrence of the impurity band conduction below 1.2 K. The magnetic field dependences of the Hall coefficient and the magnetoresistances of the samples with holes of 4∼5×10 15 cm -3 depended on the directions of the current and the magnetic field below 1.2 K, which might be attributable to the anisotropic acceptor wave functions. In the sample with holes of 1.5×10 16 cm -3 , the experimental data indicated that the Fermi level was located in the valence band below helium temperatures. Rather large negative magnetoresistances were observed below 1.2 K both in the impurity band conduction region and in the degeneracy region. Discussion is given on the origin of the negative magnetoresistances in the light of the detailed knowledge of the peculiar structure of the valence band and the acceptor state of tellurium.