Abstract
FeSi is known as a narrow-gap semiconductor showing peculiar temperature dependence of transport properties, which evoked debate for over 50 years. In this study, it is shown that the peculiar temperature dependence of the electrical conductivity σ, the Hall coefficient RH, the Hall mobility μH, the Seebeck coefficient S, and the Nernst coefficient Q of FeSi can be well explained in a model that includes the conduction and the valence band with parabolic dispersions together with the top and bottom impurity Hubbard bands. In particular, the coincidence of the hump of σ(T), the maximum of S(T), the minimum of μH(T), and the maximum of Q(T) can be attributed to the contribution from hopping conduction in the top impurity Hubbard band.
Highlights
Iron-based narrow-gap semiconductors, such as FeSi, FeSb2, and FeGa3, have attracted attention of many researchers due to their resemblance to heavy-fermion Kondo insulators.[1,2,3,4] Among the iron-based semiconductors, Battiato et al.[5] succeeded in quantitatively explaining the anomalous temperature dependence of the Seebeck coefficient S(T) and the Nernst coefficient Q(T) of FeSb2 by the phonon-drag effect by assuming three in-gap impurity bands
The reported data of σ(T), RH(T), μH(T), S(T), and Q(T) = −ν(T) in Ref. 15 on the Czochralski grown single crystal FeSi sample are shown in Figs. 1(a)–1(e), respectively
On the basis of the Hubbard-band model for the donor impurity states together with the parabolic-band model for the conduction and valence bands, simultaneous fits to the temperaturedependence data of the transport coefficients have been performed on single crystal samples of FeSi
Summary
Iron-based narrow-gap semiconductors, such as FeSi, FeSb2, and FeGa3, have attracted attention of many researchers due to their resemblance to heavy-fermion Kondo insulators.[1,2,3,4] Among the iron-based semiconductors, Battiato et al.[5] succeeded in quantitatively explaining the anomalous temperature dependence of the Seebeck coefficient S(T) and the Nernst coefficient Q(T) of FeSb2 by the phonon-drag effect by assuming three in-gap impurity bands. Sun et al.[15] measured σ(T), RH(T), μH(T), S(T), and Q(T) of a single crystal FeSi sample, where RH(T) and μH(T) denote the temperature dependence of the Hall coefficient and the Hall mobility, respectively They found that the dimensionless ratio Q/μH—a measure of energy dispersion of the charge scattering time τ(E)—exceeds that of typical semiconductors by two orders of magnitude. A complete understanding of the electrical and thermoelectric properties of FeSi has still remained elusive For another phase of iron silicides, β-FeSi2, on the other hand, whereas the low-temperature peak of S(T) had been believed to be due to the phonon-drag effect for a long time,[16,17,18,19] it has recently been proved to be attributed to hopping conduction in the impurity band.[20].
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