Hopping magnetotransport of the band-gap tuning Cu2Zn(SnxGe1-x)Se4 crystals

Resistivity, rho(T, x), of Cu2Zn(SnxGe1-x)Se-4 (CZTGeSe) single crystals with x = 0-1, investigated at temperatures between T similar to 10-320 K, exhibits an activated character within the whole temperature range, attaining a minimum at x = 0.47. Magnetoresistance (MR) of CZTGeSe with x = 0.26, 0.47 and 0.64 is positive (pMR) in all measured fields of B up to 20 T at any T between similar to 40-320 K, whereas MR of samples with x = 0 and 1 contains a negative contribution (nMR). The dependence of rho(T) at B = 0 gives evidence for a nearest-neighbor hopping (NNH) conductivity in high-temperature intervals within T similar to 200-320 K depending on x, followed by the Mott variable-range hopping (VRH) charge transfer with lowering temperature. The pMR law of ln rho(B) proportional to B-2 is observed in both hopping conductivity regimes above, provided that the nMR contribution is absent or saturated. Analysis of the rho(T) and MR data has yielded the values of the NNH activation energy and the VRH characteristic temperature, as well as those of the acceptor band width, the acceptor concentration, the localization radii of holes and the density of the localized states (DOS) at the Fermi level. All the parameters above exhibit a systematic non-monotonous dependence on x. Their extremums, lying close to x = 0.64, correspond to the minimum of a lattice disorder along with the maximum of DOS and of the acceptor concentration, as well as a highest proximity to the metal-insulator transition.