Electrical properties of β-FeSi₂ bulk crystal grown by horizontal gradient freeze method

The growth of bulk iron silicide by Horizontal Gradient Freeze (HGF) method was achieved using different growth and annealing conditions. Two types of annealing process, in-situ annealing and ex-situ annealing, were examined. Three types of samples were prepared and examined; (i) samples which were not applied any annealing processes, (ii) samples which were applied in-situ annealing, and (iii) samples which were applied both in-situ and ex-situ annealing. The influence of annealing and growth conditions upon the material qualities was examined and discussed, putting special emphasis on the structural properties and electrical properties. Results of the X-ray diffraction revealed that only the in-situ annealing was not sufficient for the peritectic reaction from α+ε eutectic to peritectic β-phase. However, it was revealed that, if the ex-situ annealing is applied after the in-situ annealing, the condition of 900 °C for 200 hours is enough for the ex-situ annealing to obtain almost single β-phase. It was also confirmed in the aspect of electrical properties that ex-situ annealing at 900 °C for 300 hours is enough to realize electrically semiconducting β-FeSi₂. The sample prepared under such a condition exhibited p-type conductivity with hole concentration and hole mobility about 5.68×10¹⁷ cm^-3 and 1.36 cm²/Vs, respectively.