Contribution to the study of point defects in bismuth

An experimental study is presented of effects on the bismuth electronic properties of point defects created by low temperature irradiation (20 K and 4 K) with neutrons or electrons. Irradiation defects at 4 K cause not only a decrease in the carrier mobilities but also a variation in the carrier numbers. This last variation is due to: 1) the created defects are electrically charged. A Frenkel pair is found to be equivalent to 0.25 donor; 2) the created defects cause an increase in the overlap of the bands and thus an increase in the carrier number (electrons and holes). The free migration of interstitials takes place in the temperature range 34-43 K with a migration energy of 0.06 eV. The vacancy type defects migrate in two main stages. The second (160 to 200 K) is also observed in the annealing curves of quenched specimens and seems to correspond to the monovacancy free migration. Neutron irradiation at 20 K have been performed on pure bismuth and bismuth doped with antimony, tin and tellurium. A simple model is presented to explain the curvature observed in the graph Δrho=f(PHI) (rho: resistivity; PHI: fluence). The temperature of the recovery stages for the doped samples are the same that those found for pure bismuth; it seems that the electrical charge of a defect does not change with the presence of impurity and that the interstitial donor states and vacancy acceptor states are ionized at all temperatures.