Variable-range hopping conductivity in Lu-doped Bi2Te3

The Seebeck coefficient enhancement due to an increase of density-of-states effective mass of electron has been found in n-type Bi1.9Lu0.1Te3. This enhancement is assumed to be related to forming the narrow and non-parabolic impurity (Lu) band with local maximum of electronic density of states lying near the Fermi level. Minimum in the specific electrical resistivity, rho, originated from change of conductivity mechanism was observed at temperature T-m approximate to 11 K. Above T-m, the rho change is due to decrease of electron mobility via acoustic phonon scattering. Below T-m, the variable-range hopping conductivity takes place. The electron hops between the localized states of the impurity energy band occur via tunneling process. Using the temperature and magnetic field dependences of rho, the localization radius of electron was estimated as approximate to 6 nm. Two parts in the magnetic field dependence of the electrical resistivity were found at temperature of 2 K. At weak magnetic fields, the rho change is in agreement with the variable-range hopping conductivity mechanism. At high magnetic fields, the positive and almost linear transverse and longitudinal magnetoresistances were observed at low temperatures. Both variable-range hopping conductivity and positive linear magnetoresistance are characteristics of disordered and inhomogeneous semiconductors. (c) 2017 Elsevier Masson SAS. All rights reserved.