Hopping conductivity in Mn-doped β-FeSi2 single crystals

Abstract

The article gives a report on resistivity measurements on Mn-doped p-type FeSi 2 single crystals and analyzes the data within the framework of different hopping conductivity models. Both the Mott ͓N. Mott and E. A. Davies, Electron Processes in Non-Crystalline Materials ͑Clarendon, Oxford, 1979͔͒ and the Shklovskii-Efros ͓B. I. Shklovskii and A. L. Efros, Electronic Properties o0066 Doped Semiconductors ͑Springer, Berlin, 1984͔͒ regimes of the variable-range hopping ͑VRH͒ conductivity are observed. It is shown that the temperature dependence of the resistivity of Mn-doped ␤-FeSi 2 crystals, which follows a VRH conduction mechanism, can be expressed by a scaling expression of the form ln͑ / 0 ͒ = Af͑T / T x ͒. The characteristic and transition temperatures, as well as the complete set of parameters describing the properties of the localized holes ͑the localization radius, the dielectric permittivity, the width of the Coulomb gap ⌬, and the values of the density of states at the Fermi level͒ are determined. The data above indicate existence of a rigid gap ␦ in the spectrum of the DOS in addition to ⌬ and point out to the polaronic nature of the charge carriers in the investigated compound.

Transport properties of β-FeSi2

“…On the other hand, the variation of W = 3.3-18.2 meV in the Co-doped samples is much higher than in the Cr-doped material, 70) indicating a corresponding high variation of the microscopic lattice disorder. 65,66) The Mn-doped p-type β-FeSi 2 exhibits a closeness to the MIT for all investigated samples with a minor dependence on the source stoichiometry, yielding T 04 = 120-410 K and T 02 = 8.2-11.9 K. 72) The values of Δ = 0.33-0.40 meV support the inference made above, whereas those of W = 4.9-8.3 meV suggest the different microscopic disorder in the investigated samples, as well. 72) For sample #L20, the values of ξ ≈ 74 Å, ξ 0 ≈ 7.5 Å (the localization radius far from the MIT, i.e., at N A ≪ N c ), κ ≈ 660, N c ≈ 3.7 × 10 19 cm −3 , and g(E F ) ≈ 2.4 × 10 18 meV −1 •cm −3 have been obtained at N A ≈ 3.3 × 10 18 cm −3 .…”

“…65,66) The Mn-doped p-type β-FeSi 2 exhibits a closeness to the MIT for all investigated samples with a minor dependence on the source stoichiometry, yielding T 04 = 120-410 K and T 02 = 8.2-11.9 K. 72) The values of Δ = 0.33-0.40 meV support the inference made above, whereas those of W = 4.9-8.3 meV suggest the different microscopic disorder in the investigated samples, as well. 72) For sample #L20, the values of ξ ≈ 74 Å, ξ 0 ≈ 7.5 Å (the localization radius far from the MIT, i.e., at N A ≪ N c ), κ ≈ 660, N c ≈ 3.7 × 10 19 cm −3 , and g(E F ) ≈ 2.4 × 10 18 meV −1 •cm −3 have been obtained at N A ≈ 3.3 × 10 18 cm −3 . 72) The values of ξ ≫ ξ 0 and κ ≫ κ 0 (where κ 0 = 29.9 is the value of the dielectric permittivity far from the MIT) 73) support the close proximity to the MIT, which is in agreement with the relations [74][75][76] where ν and η are the critical exponents of the localization radius and the dielectric permittivity, respectively.…”

“…72) For sample #L20, the values of ξ ≈ 74 Å, ξ 0 ≈ 7.5 Å (the localization radius far from the MIT, i.e., at N A ≪ N c ), κ ≈ 660, N c ≈ 3.7 × 10 19 cm −3 , and g(E F ) ≈ 2.4 × 10 18 meV −1 •cm −3 have been obtained at N A ≈ 3.3 × 10 18 cm −3 . 72) The values of ξ ≫ ξ 0 and κ ≫ κ 0 (where κ 0 = 29.9 is the value of the dielectric permittivity far from the MIT) 73) support the close proximity to the MIT, which is in agreement with the relations [74][75][76] where ν and η are the critical exponents of the localization radius and the dielectric permittivity, respectively. [74][75][76] However, the ratio of η=ν = 1.35 ± 0.12 obtained in Ref.…”

Electrical characterization and conduction mechanism of impurity-doped BaSi2 films grown on Si(111) by molecular beam epitaxy

“…where T* is the characteristic temperature, and q is the parameter determining the Mott-type (q=2) or the Shklovskii-Efros (SE) type (q=4) variable-range hopping (VRH) conduction [23][24][25][26]. Figures 5(a) Figs.…”

In-situ heavily p-type doping of over 1020 cm−3 in semiconducting BaSi2 thin films for solar cells applications

“…2(b). Non-linear behaviors were observed, meaning that the carrier transport cannot be explained by variable range hopping, [14][15][16] differently from Ga-, Cu-, and Ag-doped BaSi 2 . Similar results were obtained for other samples.…”