We report on the structural and electrical properties of iron silicides in the transformation process from ε-FeSi to β-FeSi2 and show the electrical characteristics of heterostructure p-β-Fe0.95 Mn0.05Si2/n-Si diodes formed by high-dose Fe+ and Mn+ co-implantation in Si (100). A mixture of polycrystalline ε-FeSi and β-FeSi2 with a thickness of 75 nm and the resistivity of ρ = 4.9×10-4 Ω·cm was in-situ formed during Fe+-implantation in Si (100) at 350 °C. These samples were annealed at Ta = 400-1100 °C and characterized by Rutherford backscattering spectrometry, van der Pauw and X-ray diffraction. Single β-FeSi2 layers with ρ = 0.31 Ω·cm were formed after annealing at Ta = 600 °C. Although the samples with Ta<600 °C exhibited p-type conductivity (hole concentrations of p = 5.3-11×1020 cm-3 and hole mobilities of μh = 8.7-32 cm2/V/s), the samples with Ta≥600 °C presented n-type conductivity (n = 4.2-14×1016 cm-3 and μe = 220-520 cm2/V/s). The origin of p-type conductivity may be due to contribution of Fe-rich β-FeSi2, while that of the electron carrier could be related to the formation of stoichiometric β-FeSi2, in which the predominant impurity phosphorous atoms remaining in the n-Si substrates could be electrically activated as donors in β-FeSi2 by high-temperature annealing. The I-V and C-V characteristics of the p-β-Fe0.95Mn0.05Si2/n-Si(100) diodes indicated that the impurity distribution of the pn junction is linearly graded, which leads to a high ideality factor of η = 4.4.
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