We report on the structural and electrical properties of iron silicides in the transformation process from epsilon -FeSi to beta -FeSi2 and show the electrical characteristics of heterostructure p-beta -Fe0.95S Mn0.05Si2/n-Si diodes formed by high-dose Fe+ and Mn+ co-implantation in Si (100). A mixture of polycrystalline epsilon -FeSi and beta -FeSi2 with a thickness of 75 nm and the resistivity of rho = 4.9 x 10(-4) Ohm .cm was in-situ formed during Fe+-implantation in Si (100) at 350 degreesC. These samples were annealed at To = 400-1100 degreesC and characterized by Rutherford backscattaring spectrometry, van der Pauw and X-ray diffraction. Single beta -FeSi2 layers with rho = 0.31 Ohm .cm were formed after annealing at Ta = 600 degreesC. Although the samples with Ta < 600C exhibited p-type conductivity (hole concentrations of p = 5.3-11 x 10(20) cm(-3) and hole mobilities of mu (h) = 8.7-32 cm(2)/V/s), the samples with Ta greater than or equal to 600 degreesC presented n-type conductivity (n = 4.2-14 x 10(16) cm(-3) and mu (e) = 220-520 cm(2)/V/s). The origin of p-type conductivity may be due to contribution of Fe-rich beta -FeSi2, while that of the electron carrier could be related to the formation of stoichiometric beta -FeSi2, in which the predominant impurity phosphorous atoms remaining in the n-Si substrates could be electrically activated as donors in beta -FeSi2 by high-temperature annealing. The I-V and C-V characteristics of the p-beta -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 eta = 4.4.