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 (Eg) 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.