Formation of polycrystalline β-FeSi₂ layers by ion-implantation and their optical properties

Polycrystalline β-FeSi₂ was made by ion beam synthesis (IBS) using implantation of Fe⁺ ions into Si. Results from two-step annealing (2SA) and three-step annealing (3SA) processes are discussed. X-ray diffraction data exhibited that for 3SA samples, β-FeSi₂ is grown at specific annealing conditions, whereas it is always formed for 2SA samples. The formation of β-FeSi₂ layer with thickness of 59-79 nm was confirmed by Rutherford backscattering measurements. The 3SA-sample showed a direct band-gap energy (E_g) of 0.88 eV and 0.80 eV for the 2SA sample. In the 2 K photoluminescence spectra, two emissions at 0.786-0.808 eV were ascribed to β-FeSi₂. Similar features were obtained for β-FeSi₂ crystals prepared by horizontal gradient freeze and electron beam deposition (EBD) methods. p-Type β-FeSi₂ layers were fabricated on n-type Si (100) substrates by Mn⁺ ion-implantation into EBD-grown β-FeSi₂ layers and subsequent annealing.