Anisotropy and Annealing Behavior in Extrinsic Single-Crystal Tellurium

Abstract

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.