Thermopower, Electrical and Hall Conductivity of Undoped and Doped Iron Disilicide Single Crystals

Abstract

The electrical transport properties of β-FeSi2 single crystals have been investigated in dependence on the purity of the source material and on doping with 3d transition metals. The transport properties included are electrical conducticvity, Hall conductivity and thermopower mainly in the temperature range from 4K to 300K. The single crystals have been prepared by chemical transport reaction in a closed system with iodine as transport agent. In undoped single crystals prepared with 5N Fe both electrical conductivity and thermopower depend on the composition within the homogeinity range of β-FeSi2 which is explained by different intrinsic defects at the Sirich and Fe-rich phase boundaries. In both undoped and doped single crystals impurity band conduction is observed at low temperatures but above 100K extrinsic behaviour determined by shallow impurity states. The thermopower shows between 100K and 200K a significant phonon drag contribution which depends on intrinsic defects and additional doping. The Hall resistivity is considered mainly with respect to an anomalous contribution found in p-type and n-type single crystals and thin films. In addition doped single crystals show at temperatures below about 130K an hysteresis of the Hall voltage. These results make former mobility data uncertain. Comparison will be made between the transport properties of single crystals and polycrystalline material.

Electrical properties of Co-doped β -FeSi2 crystals

“…Below 50 K, R H becomes nearly temperature independent with values in the range 1 ϫ10 3 -5ϫ10 3 Fig. Below 50 K, R H becomes nearly temperature independent with values in the range 1 ϫ10 3 -5ϫ10 3 Fig.…”

“…4 Device applications require the ability to control electrical properties such as the type of conduction and the doping level. 3,[8][9][10] In this study, we investigated ␤-FeSi 2 crystals grown by chemical vapor transport which were doped in situ with varying amounts of Co in the starting material. 5 Mössbauer effect 6 and electron spin resonance 7 studies showed that Co is a substitutional donor on a Fe site.…”

Solution growth of n-type - single crystals using Sn solvent

“…reported that conduction type changes from p-to n-type when the purity of Fe-source changes from 4 to 5 N [19]. Conduction type also changes from p-to n-type when the composition of Fe-Si source changes from Fe-rich to Si-rich.…”

Transport properties of β-FeSi2

“…Semiconducting iron disilicide or β-FeSi 2 is a promising compound for optoelectronic devices on Si substrates, photonics, photovoltaics, and is attractive for high-temperature thermoelectric materials. [1][2][3] Because of its high optical absorption coefficient (exceeding 10 5 cm −1 at 1.0 eV) and abundant element resources in the Earth's crust, β-FeSi 2 is expected to be a promising photovoltaic material [4][5][6] with a theoretical energy conversion efficiency of about 16-23%. 4,5) The direct band gap of 0.83-0.87 eV (Refs.…”