Low-temperature electrical conductivity of ion-beam irradiated Bi-Sb films

Bismuth-antimony alloys are among the most studied topological insulators and also have very promising thermoelectric properties. In addition, in the amorphous state they exhibit superconductivity with critical temperatures in the range 6.0-6.4 K. In this work, we have prepared and studied different polycrystalline films of Bi100 - x Sb (x )(x = 0, 5, 10, 15), and we have induced, through ion beam irradiation, significant damage in their internal structure with the aim of amorphizing the material. Specifically, we have irradiated Bi ions in the 10-30 MeV range, exploiting the capabilities of a 5 MV ion beam accelerator of tandem type. We have characterized the Bi-Sb films before and after irradiation from a morphological and structural point of view and measured their electrical resistivity from room temperature to near 2 K, to evaluate the influence of the preparation method and degree of disorder. We have found that the studied Bi-Sb system always behaves as a small energy gap semiconductor that follows the empirical Meyer-Neldel rule, which correlates the conductivity prefactor with the exponential value of the energy gap.