This study deals with structural and optical properties of β-FeSi
b>2b> layers produced
by direct ion
beam mixing of Fe/Si
bilayers with Xe ions. By irradiation of 35 nm Fe on Si, at 600 °C with 205 keV Xe to 2×10
16 ions/cm
2, the formation of
border=0 SRC=/images/glyphs/BQ1.GIF>105 nm single-phase β-FeSi
b>2b> layers was achieved. Their structures were analyzed
by Rutherford
backscattering spectroscopy, X-ray diffraction, conversion electron Möss
bauer spectroscopy, high resolution transmission electron microscopy, and photo-a
bsorption. The structural analyses revealed that the β-FeSi
b>2b> layers grow in the form of irregularly shaped
crystal grains, with a pronounced surface morphology,
but with a rather sharp silicide/silicon interface. The grains that originate from the interface are epitaxially oriented relative to the Si(100) su
bstrate. Optical a
bsorption, as compared with that in β-FeSi
b>2b> layers produced
by ion
beam synthesis or co-sputter deposition, indicates a direct
band gap of 0.92 eV. A pronounced surface roughness of the ion
beam mixed layers yielded photo-a
bsorption approximately three times higher as compared with the other two sets of samples. The
band gap stays nearly constant over the temperature range from 80 to 295 K. This is tentatively assigned to a high degree of structural disorder and stress induced in the ion
beam mixed β-FeSi
b>2b> layers.