Anisotropy and Annealing Behavior in Extrinsic Single-Crystal Tellurium

Electrical resistivity and Hall coefficient measurements have been made on tellurium specimens to determine anisotropy characteristics. Single-crystal boules of differing impurity contents were cut into rectangular samples with one edge parallel to the c axis of the parent crystal. For each sample, the electrical resistivity was measured in the temperature range 78°K to about 300°K, first with the current flow parallel to the c axis (ρ∥) and then with the current flow perpendicular to the c axis (ρ∥). The Hall coefficient was similarly measured, first with the magnetic field perpendicular to the c axis (R∥) and then with the magnetic field parallel to the c axis (R∥). For samples not given special heat treatment prior to measurement, the anisotropy ratios ρ∥/ρ∥ and R∥/R∥ at a fixed temperature tended to increase as the carrier concentration (R∥e)−1 decreased. Annealing at 350°C in helium at 0.5 atm pressure for 60 to 160 h caused initially different anisotropy ratios to approach the values: ρ∥/ρ∥=1.41±0.11, R∥/R∥=1.29±0.04. Annealing also produced a trend toward a common mobility, R∥/ρ∥=5700±400 cm2 V−1 sec−1 at 78°K, for samples with (R∥e)−1 ranging from 1.8×1015 cm−3 to 1.9×1017 cm−3 at 78°K.