Piezomagnetoresistance Anisotropy of n‐Ge in Strong Magnetic Fields near the Metal–Insulator Transition

Abstract

Over the temperature range 2 to 77 K longitudinal and transverse magnetoresistance (MR) measurements are performed on Ge:Sb crystals in magnetic fields u p to 200 kOe. The crystals used are uniaxially compressed along the (1 11) axis and have electron concentrations between 0.82 x 1017 and 6.2 X lo1'A large MR anisotropy is found to arise chiefly from the anisotropy of the energy gap between the Fermi level and the mobility edge. A correlation is shown to exist between the temperature dependences of the negative and positive MR's in high magnetic fields. From an analysis of the concentration and temperature dependences of the MR anisotropy, i t is inferred that for n > n, there exist certain regions of electron concentrations and temperatures where, despite the metallic character of conduction, effects show up which are typical of impurity band charge carriers. P u t another way, the electron states in these regions are intermediate between band states, for which the scattering is weak, and virtually localized states, for which the scattering is strong.

On the Anisotropy of Scattering in Doped n‐Ge at Low Temperatures

“…As the conductivity on both the metallic and dielectric sides of the MIT, with n, < n < 10n, and n < n,, respectively, depends on the degree of overlap of the donor wave functions [6,7], the processes of electron tunnelling underneath the potential barrier (diffusion conductivity) should make a certain contribution to the kinetic effects. It stands to reason that tunnelling plays an important role when the electron energy E is less than the impurity-potential fluctuation amplitude y.…”

“…This problem has given detailed treatment (see, e.g., [6,7,11,131) in our analysis of the temperature, uniaxial pressure, and magnetic field dependences of conductivity, thermoelectric power, and Hall coefficient.…”