M. A. Shakhov

Influence of scattering and interference effects on the low-temperature magnetotransport of Cu2ZnSnS4 single crystals

Activated resistivity, ρ(T), and positive magnetoresistance (MR) are observed in Cu2ZnSnS4 single crystals within the temperature interval between T ∼ 2 and 300 K in pulsed magnetic fields of B up to 20 T. Between T ∼ 50 and 150 K, the charge transfer is described by the Mott variable-range hopping (VRH) transport over localized states of the defect acceptor band with width W ∼ 12–25 meV. Up to the highest applied fields, MR follows the law ln ρ(B) ∝ B2 pertinent to the VRH conduction at λ ≫ a, where λ is the magnetic length and a is the localization radius. The joint analysis of the MR and ρ(T) data yielded a series of microscopic parameters, including the values of a ≈ 22–45 A, depending on the proximity of a sample to the metal-insulator transition. However, below T ∼ 3–4 K the Shklovskii-Efros VRH conduction is observed. Here, the behavior of MR changes drastically, exhibiting a sharp contraction of the quadratic MR region and transformation of the MR law into those of ln ρ (B) ∝ B2/3 or ∝ B3/4 when B...

Hopping magnetotransport of the band-gap tuning Cu2Zn(Sn x Ge1-x )Se4 crystals.

Resistivity, ρ(T, x), of Cu2Zn(Sn x Ge1-x )Se4 (CZTGeSe) single crystals with x  =  0-1, investigated at temperatures between T ~ 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 ~40-320 K, whereas MR of samples with x  =  0 and 1 contains a negative contribution (nMR). The dependence of ρ(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 pMR law of lnρ(B) [Formula: see text] B (2) is observed in both hopping conductivity regimes above, provided that the nMR contribution is absent or saturated. Analysis of the ρ(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.

Mechanisms of charge transfer and electronic properties of Cu 2 ZnGeS 4 from investigations of the high-field magnetotransport

Recent development of the thin film solar cells, based on quaternary compounds, has been focused on the Ge contain compounds and their solid solutions. However, for effective utilization of Cu2ZnGeS4, deeper investigations of its transport properties are required. In the present manuscript, we investigate resistivity, ρ (T), magnetoresistance and Hall effect in p-type Cu2ZnGeS4 single crystals in pulsed magnetic fields up to 20 T. The dependence of ρ (T) in zero magnetic field is described by the Mott type of the variable-range hopping (VRH) charge transfer mechanism within a broad temperature interval of ~100–200 K. Magnetoresistance contains the positive and negative components, which are interpreted by the common reasons of doped semiconductors. On the other hand, a joint analysis of the resistivity and magnetoresistance data has yielded series of important electronic parameters and permitted specification of the Cu2ZnGeS4 conductivity mechanisms outside the temperature intervals of the Mott VRH conduction. The Hall coefficient is negative, exhibiting an exponential dependence on temperature, which is quite close to that of ρ(T). This is typical of the Hall effect in the domain of the VRH charge transfer.

High-temperature magnetism and microstructure of a semiconducting ferromagnetic (GaSb)1−x(MnSb)x alloy

We have studied the properties of relatively thick (about 120 nm) magnetic composite films grown by pulsed laser deposition using the eutectic compound (GaSb)0.59(MnSb)0.41 as target for sputtering. For the studied films we have observed ferromagnetism and an anomalous Hall effect above room temperature, confirming the presence of spin-polarized carriers. Electron microscopy, atomic and magnetic force microscopy results suggest that the films under study have a homogenous columnar structure in the bulk while MnSb inclusions accumulate near the surface. This is in good agreement with the high mobility values of charge carriers. Based on our data we conclude that the magnetic and magnetotransport properties of the films at room temperature are defined by the MnSb inclusions.

Magnetotransport of Cu 2 ZnSnS 4 single crystals in two regimes of variable–range hopping conduction

The resistivity, ρ(T), and the magnetoresistance (MR) of Cu2ZnSnS4 (CZTS) single crystals are investigated at temperatures T = 2–300 K in pulsed magnetic fields of B up to 20 T. The Mott variable–range hopping (VRH) conductivity over localized states of the defect acceptor band is observed between T ~ 50–150 K. The Shklovskii–Efros (SE) VRH conduction over the states of the Coulomb gap is found below T ~ 3–4 K. The positive MR is observed at all temperatures and magnetic fields, its value decreasing with T. In the Mott VRH conduction region, MR follows the law ln ρ(B) ∝ B2 up to the highest applied fields. The joint analysis of the resistivity and MR data in this region has yielded values of the localization radius as well as a set of important microscopic parameters, including the mobility threshold in the acceptor band, the values of the density of localized states near the Fermi level and the critical concentration of the metal–insulator transition. In the SE region, the MR law above is observed only in much smaller fields, transformed into those of lnρ(B) ∝ B2/3 or ∝ B3/4 when B increases. Such transformation, accompanied by a strong increase of the localization radius, give evidence for an important role of scattering and interference phenomena in the VRH conduction at low temperatures.