Effect of implant conditions on the optical and structural properties of β-FeSi2

Semiconducting precipitates of β-FeSi₂ have been successfully fabricated in silicon by high dose Fe⁺ implantation (typically 1.5 × 10¹⁶ Fe cm^-2 at 200keV). Room temperature electroluminescence (EL) at 1.5μm has been observed from light emitting diodes (LED´s) incorporating this type of structure. This study is to evaluate how the microstructure and optical properties are affected by the implantation parameters, in particular the role of implantation temperature, when high beam current densities are being used. This was done in order to evaluate whether the implant period could be reduced to a commercially realistic time without adversely affecting the optical properties. In this study the implantation temperature was varied and the resulting structures investigated (before and after annealing) using optical absorption, Fourier Transform Infrared Spectroscopy (FTIR), Rutherford backscattering spectroscopy (RBS) and cross sectional transmission electron microscopy (XTEM). A 70 meV decrease in the optical band gap was observed between a sample implanted at 250°C and one implanted at 550°C, a shift in the FTIR spectrum was also observed. RBS and XTEM measurements showed that this change was associated with a change from a surface to a buried silicide layer, with the latter also exhibiting room temperature EL.