Formation of beta -FeSi sub(2) precipitates at the SiO sub(2)/Si interface by Fe super(+) ion implantation and their structural and optical properties

Iron-disilicide precipitates were formed by two different processes; (i) Fe super(+) ion implantation in Si and subsequent dry oxidation and (ii) Fe super(+) ion implantation at the interface of SiO sub(2)/Si and subsequent annealing. These samples were characterized by Rutherford backscattering spectrometry (RBS), transmission electron microscope (TEM), X-ray diffraction (XRD), photothermal deflection spectroscopy (PDS) and photoluminescence (PL). The implanted Fe concentrated at the SiO sub(2)/Si interface and formed beta -FeSi sub(2) precipitates by both processes. However, part of the implanted Fe still remained in SiO sub(2) and possibly formed Fe precipitates through the process (ii). It is notable that a clear interface has formed through the process (i) whereas a defect rich region was produced in Si near the Si/SiO sub(2) interface by the process (ii). Weak optical absorption above 0.8 eV corresponding to the band gap of beta -FeSi sub(2) was confirmed for both processes. It is noted that sharp PL was observed at 0.81 eV at 5 K for the sample (i) whereas broad PL was observed for the sample (ii). The origin of the PL was discussed from the point of view of direct transition of strained beta -FeSi sub(2), a shallow acceptor level in a non-intentionally doped p-type beta -FeSi sub(2) and defect levels, in particular dislocations in Si.