Mechanisms of hopping conductivity of p-CdSb:Ni in magnetic field

Hopping conductivity in single crystals of the group II-V anisotropic diluted magnetic semiconductor p-CdSb:Ni, oriented along the[100] (1),[010] (2) and[001] (3) axes, is investigated in zero and pulsed magnetic fields B. At B=0 the Mott variable-range hopping (VRH) conductivity is observed in 2, and the Shklovskii-Efros VRH conductivity in 1 and 3 at T≤2.5 K. However, in weak fields of B<6 T temperature dependence of the resistivity gives evidence for the Mott VRH conductivity in 1 below ∝4.2 K, whereas in 2 and 3 the nearest-neighbour hopping (NNH) conductivity is observed between 3-4.2 K and between 1.5-4.2 K, respectively. Eventually, in high magnetic fields of B up to ∝15 T and T≤4.2 K only the NNH conductivity is observed in all investigated samples. The analysis of the resistivity data yields the set of microscopic parameters, such as the localization radius, the widths of the Coulomb gap and of the impurity band, the density of the localized states and the anisotropy coefficients, as well as the values of the acceptor concentration and the dielectric permittivity. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)