Single crystalline β-FeSi₂ grown using high-purity FeSi₂ source

We have investigated the effect of FeSi₂ source purity on the electrical property of β-FeSi₂ grown from solution. A high-purity FeSi₂ source avoided a contamination of Cu and W metals was synthesized by melting a high-purity Fe (5N) and Si (5N-up) in a quartz ampoule. Glow discharge mass spectrometry revealed that the purity of the FeSi₂ source synthesized using 5N-Fe and a quartz-ampoule-melting process is one order of magnitude higher than that of the conventional arc-melted FeSi₂ source using 4N-Fe. The β-FeSi₂ crystals grown using the high-purity FeSi₂ and Zn solvent showed n-type conduction, whereas those grown using the arc-melted FeSi₂ showed p-type. The carrier concentration of the n-type crystals was (4.9-6.3) × 10¹⁸ cm^{- 3}, which was more than 10 times higher than that of the p-type crystals (5.2 × 10¹⁷ cm^{- 3}). From the ICP-MS and SIMS analysis of the grown crystals, we found that dominant impurity concentrations (Cr, Mn, Co, Ni, Cu, Zn and W) in the p-type crystals were higher than those in the n-type ones. Therefore, the p-type conductivity of undoped crystals grown using Zn solvent results from unintentional doping by the high impurity level of the used FeSi₂ source.