Effect of Mn-doping on the electrical properties of Cu2GeSe3

In this work we report the temperature dependence of the resistivity ρ of p-Cu2GeSe3 and manganese-doped p-Cu2GeSe3 at low temperature. It was found that for a intrinsic sample ρ   obeys the Shklovskii–Efros-type variable-range hopping resistivity law ρ(T)=ρ0exp[(T0/T)1/2] in the temperature range from 4 to 63 K. This behaviour is governed by generation of a Coulomb gap Δ=78 meV in the density of localized states. We find a low activation term T0=0.24 K, which is an indication of a large localization length ξ. For Mn-doped sample a metal–insulator transition (MIT) is observed at T=65 K. On the basis of the Mott criterion for metal–insulator transition, the critical carrier density nc is determined. From the analysis of resistivity data it is concluded that Mn acts as acceptor impurity.