β-FeSi2 in (111)Si and in (001) Si formed by ion-beam synthesis

Abstract

Ion-beam synthesis of β-FeSi2 is demonstrated both in (111) Si and (001) Si substrates by 450 keV Fe ion implantation at elevated temperatures using a dose of 6×1017 Fe/cm2 and subsequent annealing at 900 °C. The structure of the buried layers has been analyzed using Rutherford backscattering spectrometry, x-ray diffraction, and (cross-section) transmission electron microscopy. In (111) Si an epitaxial layer is formed consisting of grains with lateral dimensions of approximately 5 μm. Epitaxy of β-FeSi2 (110) and/or (101) planes parallel to the (111) Si substrate plane is observed. In (001) Si a layer is formed consisting of grains with lateral dimensions of typically 0.5 μm. Several grain orientations have been observed in this material, among others β-FeSi2 {320}, {103}, and {13,7,0} parallel to (001) Si. Selected (111) Si samples were investigated optically using spectroscopic ellipsometry, and near-infrared transmittance and reflectance spectroscopy. The results confirm that the β-FeSi2 layer has an optical band gap of 0.87 eV. The ellipsometry results indicate that the layers formed by ion-beam synthesis are more dense than those formed by surface growth techniques. Hall measurements show that the β-FeSi2 layers obtained are p type. Mobilities observed are 1–4 cm2/V s at room temperature and approximately 25 cm2/V s at liquid-nitrogen temperature. These results show that the electrical properties of ion-beam-synthesized β-FeSi2 is comparable with those of surface-grown material. The results confirm that optoelectronic applications of β-FeSi2 are limited.