The mechanism of charge transfer in Bi$_2$(Tе$_{0.9}$Se$_{0.1}$)$_3$ solid solution thin films

The conductivity, Hall effect, and magnetoresistance of Bi$_2$(Tе$_{0.9}$Se$_{0.1}$)$_3$ solid solution thin films are studied in a wide temperature range from 2.5 to 300 K and in high magnetic fields of up to 8 T. It is found that the conductivity of Bi$_2$(Tе$_{0.9}$Se$_{0.1}$)$_3$ solid solution thin films is of the insulator type, whereas the conductivity of the corresponding bulk single crystals is of metallic type. It is inferred that, at high temperatures (100–300 K), the conductivity is controlled mainly by thermally activated charge-carrier transport over extended states in the conduction band, with an activation energy of about 15 meV. At lower temperatures (2.5–70 K), conductivity controlled by charge-carrier hopping between localized states in a narrow energy region close to the Fermi level is dominant. From the magnetoresistance and conductivity data, the localization radius, the density of localized states, and the average charge-carrier hopping length are estimated.