Molecular beam epitaxial growth of Fe ( Si 1 − x Ge x ) 2 epilayers

The semiconducting silicides offer significant potential for use in optoelectronic devices. Full implementation of the materials, however, requires the ability to tailor the energy gap and band structure to permit the synthesis of heterojunctions. One promising approach is to alloy the silicides with Ge. As part of an investigation into the synthesis of semiconducting silicide heterostructures, a series of β - Fe ( Si 1 − x Ge x ) 2 epilayer samples, with nominal alloy content in the range 0 ⩽ x ⩽ 0.15 , have been prepared by molecular beam epitaxy on Si(100). We present results of the epitaxial and crystalline quality of the films, as determined by reflection high-energy electron diffraction, Rutherford backscattering spectroscopy, and double crystal x-ray diffraction, and of the band gap dependence on the alloy composition, as determined by Fourier transform infrared spectroscopy. We observe a reduction in band gap with increasing Ge content, in agreement with previous theoretical predictions [Tani et al. , J. Solid State Chem. 169, 19 (2002)]. However we also observe Ge segregation in β - Fe ( Si 1 − x Ge x ) 2 epilayers when x ⩾ 0.04 .