Formation and characterization of FeSi(2) thin films and precipitates prepared by metal vapor vacuum arc (MEVVA) ion implantation

Iron ion implantation into silicon using a metal vapor vacuum arc (MEVVA) ion source was performed to synthesize continuous β-FeSi₂ thin films and nanometer scale β-FeSi₂ precipitates. The implantation was performed at various conditions and the effects of implantation temperature, implantation dose, as well as thermal annealing conditions were studied. The samples were characterized by employing various analytical techniques including Rutherford backscattering spectrometry (RBS), x-ray diffraction (XRD), transmission electron microscopy (TEM), optical absorption (OA), photoluminescence (PL) and electric property measurements.; The experimental results indicated that whether a FeSi₂ stoichiometric layer or FeSi₂ precipitates were formed would be determined by the implantation dose and annealing temperature. However, the phase formation was determined by the implantation temperature and the annealing conditions. At the same annealing temperature, β-FeSi₂ was formed when the implantation was carried out at an elevated temperature, while the formation of γ-FeSi₂ and β-FeSi₂ coherent with the silicon substrate dominated when the implantation was done at low temperature followed by rapid thermal annealing (RTA). For the first time, metastable γ-FeSi ₂ precipitates with a large size of 20∼60 nm in diameter were observed after annealing at 850°C for 10 hours. Also, highly strained β-FeSi ₂ precipitates completely coherent with the silicon substrate were observed for the first time. In addition, the formation and distribution of the dislocation loops were successfully controlled in the present work by varying the implantation temperature. For the first time, ion beam synthesis of FeSi₂ precipitate layers was achieved in Si with a complete elimination of dislocations or with the dislocations formed well separated from the precipitate layers.; Measurements of optical absorption indicated that the band gap properties of the synthesized β-FeSi₂ layer depended on the Fe atom fraction in the silicon substrate. A direct band gap property appeared when the Fe atom fraction was under the stoichiometric value of 33%, while a mixed band gap property was observed when the Fe atom fraction was close or equal to the stoichiometric value. Further analysis of the lattice parameters obtained from the XRD spectra demonstrated that compression along the c-axis resulted in a change of the band property from direct to indirect.; Strong photoluminescence (PL) spectra were observed in the samples implanted at both elevated and low temperatures with low implanted doses. The strain effect on PL properties was obtained by comparing the PL spectra of the samples implanted at low temperature with and without β-FeSi₂ precipitates coherent with the silicon substrate. It was found that the emission peak energy of the highly-strained β-FeSi₂ moved to a lower value compared to that of strainfree sample. Furthermore, by comparing the microstructures and the PL properties of the samples implanted at high and low temperatures, the origins of the PL in these samples could be distinguished and identified to be from β-FeSi₂ precipitates or from crystal defects in the samples. Our experimental results give a direct proof that the broad PL peak of Gaussian shape at 1.55 μm should be from the contribution of β-FeSi ₂ precipitates.