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

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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.

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