Structural and optical characterization of β-FeSi 2 layers on Si formed by ion beam synthesis

Abstract

Structural and optical properties have been investigated for surface β-FeSi 2 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-FeSi 2 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-FeSi 2 Si (100) and β-FeSi 2 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-FeSi 2 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 10 4 cm −1 near the absorption edge for all samples.