Electrical Properties of Tellurium Crystals at Very Low Temperatures : Experiment with Liquid Helium

The electrical conductivity, the Hall effect, and the magneto-resistance effect are investigated with the specimens of highly purified tellurium single crystal and 0.01 per cent antimony added tellurium crystal over the temperatures ranging from ambient to the liquid helium temperatures (1.7°K). The former specimen is found to be a p-type extrinsic semiconductor below 167°K, above which intrinsic excitation results. By analysing the data of conductivity and Hall coefficient, taking into account the scattering mechanisms of current carriers together with their degeneracy, and also by assuming the additivity of ionized impurity scattering, lattice scattering, and dislocation scattering, we deduced the Hall mobility of holes μ cm^2/volt-sec as expressed by the next formula. 1/μ=1/μ_i+1/μ_l+1/μ_d=5.7×10^T^ln(1+3.8×10^T^2)+5.05×10^T^+4.0×10^T^, where μ_i is the mobility associated with the impurity scattering as calculated by Conwell and Weisskopf, μ_l is that corresponding to the lattice scattering, and μ_d is that associated with the dislocation scattering which was treated by Dexter and Seitz. The corresponding term μ_n which is ascribable to the neutral impurity scattering seems to be negligibly small. Both the excitation energy required to raise an electron from the valence band to the acceptor impurity and the height of the electrochemical potential above the valence band are found to tend to zero as the temperature approaches to zero