Fabrication of heterostructure p-β-Fe_0.95Mn_0.05Si₂/n-Si diodes by Fe⁺ and Mn⁺ co-implantation in Si(100) substrates

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-Fe_0.95 Mn_0.05Si₂/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 μ_h = 8.7-32 cm²/V/s), the samples with Ta≥600 °C presented n-type conductivity (n = 4.2-14×10¹⁶ cm^-3 and μ_e = 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-Fe_0.95Mn_0.05Si₂/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.