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

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

Spectroscopic ellipsometry study of Cu2ZnSnS4 bulk poly-crystals

5 pags., 3 figs., 3 tabs.The linear optical properties of Cu2ZnSnS4 bulk poly-crystals have been investigated using spectroscopic ellipsometry in the range of 1.2–4.6 eV at room temperature. The characteristic features identified in the optical spectra are explained by using the Adachi analytical model for the interband transitions at the corresponding critical points in the Brillouin zone. The experimental data have been modeled over the entire spectral range taking into account the lowest E0 transition near the fundamental absorption edge and E1A and E1B higher energy interband transitions. In addition, the spectral dependences of the refractive index, extinction coefficient, absorption coefficient, and normal-incidence reflectivity values have been accurately determined and are provided since they are essential data for the design of Cu2ZnSnS4 based optoelectronic devices. Published by AIP Publishing.The research leading to the presented results was partially supported by the European Project INFINITE-CELL (Ref. H2020-MSCA-RISE-2017-777968, 2017–2021, www.infinitecell. eu) and the Spanish MINECO Projects “WINCOST” (ENE2016-80788-C5-2-R) and PHOTOMANA (TEC2015- 69916-C2-1-R). The authors from the Institute of Applied Physics appreciate the financial support from STCU 6224 and from the Institutional Project No. CSSDT 15.817.02.04APeer reviewe

Magnetotransport and conductivity mehanisms in Cu2ZnSnxGe1-xS4 single crystals

Resistivity, ρ(T), and magnetoresistance (MR) are investigated in the Cu2ZnSnxGe1−xS4 single crystals, obtained by the chemical vapor transport method, between x = 0–0.70, in the temperature range of T ~ 50–300 K in pulsed magnetic field of B up to 20 T. The Mott variable-range hopping (VRH) conductivity is observed within broad temperature intervals, lying inside that of T ~ 80–180 K for different x. The nearest-neighbor hopping conductivity and the charge transfer, connected to activation of holes into the delocalized states of the acceptor band, are identified above and below the Mott VRH conduction domain, respectively. The microscopic electronic parameters, including width of the acceptor band, the localization radius and the density of the localized states at the Fermi level, as well as the acceptor concentration and the critical concentration of the metal-insulator transition, are obtained with the analysis of the ρ(T) and MR data. All the parameters above exhibit extremums near x = 0.13, which are attributable mainly to the transition from the stannite crystal structure at x = 0 to the kesterite-like structure near x = 0.13. The detailed analysis of the activation energy in the low- temperature interval permitted estimations of contributions from different crystal phases of the border compounds into the alloy structure at different compositions