Hopping magnetotransport of the band-gap tuningCu2Zn(SnxGe1-x)Se4 crystals

Abstract

Resistivity,  (T, x), of Cu2Zn(SnxGe1-x)Se4 (CZTGeSe) single crystals with x = 0  1 exhibits an activated character within the whole investigated temperature range between T ~ 10  320 K, attaining a minimum at x = 0.5. Magnetoresistance (MR) of CZTGeSe with x = 0.3, 0.5 and 0.7 is positive (pMR) in all magnetic fields of B up to 20 T at any T between ~ 40  320 K, whereas MR of samples with x = 0 and 1 contains a negative contribution (nMR). The dependence of  (T) at B = 0 gives evidence for a nearest-neighbor hopping (NNH) conductivity in high-temperature intervals within T ~ 200  320 K depending on x, followed by the Mott variable-range hopping (VRH) charge transfer with lowering temperature. The MR law of ln  (B)  B2 is observed in both hopping conduction regimes above, provided that the nMR contribution is absent or saturated. Analysis of the  (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, corresponding to the minimum of a lattice disorder along with the maximum of DOS and of the defect concentration, as well as a highest proximity to the metal-insulator transition, suggest an optimum for electronic properties composition of CZTGeSe near x ~ 0.6  0.7.