The Electrical Properties of Bismuth Telluride

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Abstract
Measurements of the electrical conductivity, Hall coefficient, thermoelectric power and Nernst coefficient on specimens cut from zone melted Bi2 Te3 and on a single crystal are described. The current flow was parallel to the cleavage planes and the galvanomagnetic effects of the single crystal were measured with the magnetic field perpendicular and parallel to the cleavage planes. For the other specimens the Hall and Nernst coefficients were measured with the magnetic field perpendicular to the cleavage planes. The temperature range was 100°K to 600°K and specimens with a wide variation of impurity content were used. Analysis of the thermoelectric power and conductivity in the extrinsic range indicated that the specimens were partially degenerate, and when allowance is made for this, the temperature dependence of mobility is T-1.63 for electrons and T-1.94 for holes. In the high temperature range the conductivity measurements yield a value of the energy gap at 0°K of 0.21 eV. The temperature dependence of the Hall coefficient in the extrinsic range is anomalous and the explanation is not known. The Nernst coefficient Q exhibits the general behaviour expected for a semiconductor, and it is shown that it obeys a relation which can be derived from Moreau's relation, Q being proportional to TRσd2E/dT2 (thermoelectric power = dE/dT, Hall coefficient = R, conductivity = σ).

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