Structural and optical properties have been investigated for surface β-FeSi2 layers on Si(100) and Si(111) formed by ion beam synthesis using 56Fe ion implantations with three different energies (140-50 keV) and subsequent two-step annealing at 600 °C and up to 915 °C. Rutherford backscattering spectrometry analyses have revealed Fe redistribution in the samples after the annealing procedure, which resulting in a Fe-deficient composition in the formed layers. X-ray diffraction experiments confirmed the existence of /gb-FeSi2 by annealing up to 915 °C, whereas the phase transformation from the β to α phase has been induced at 930 °C. In photoluminescence measurements at 2 K, both β-FeSi2 Si(100) and β-FeSi2 Si(111) samples, after annealing at 900-915 °C for 2 h, have shown two dominant emissions peaked around 0.836 eV and 0.80 eV, which nearly coincided with previously reported PL emissions from the sample prepared by electron beam deposition. Another β-FeSi2 Si(100) sample has shown sharp emissions peaked at 0.873 eV and 0.807 eV. Optical absorption measurements at room temperature have revealed the allowed direct bandgap of 0.868-0.885 eV as well as an absorption coefficient of the order of 104 cm-1 near the absorption edge for all samples.
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