Lattice-strain control of semiconducting silicide for 1.5μm light-emission and wave-length modulation

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Semiconducting silicide β-FeSi_2 with a direct energy gap of 1.5μm is attractive for opto-electronics applications. To apply β-FeSi_2 to multi-wavelength devices, modulation of the energy gap is necessary. Doping with Ge into β-FeSi_2 will realize the energy gap modulation caused by lattice strains, as predicted by a theoretical calculation. For this purpose, precise concentration control of constituent is very important. Our idea to achieve this is controlled diffusion and segregation of Si and Ge by utilizing [a-Si/a-FeSiGe]_n multi-layered structures.We have investigated solid-phase growth of [a-Si/a-FeSiGe]_n multilayered structures has been investigated. After annealing at 700°C, [a-SiGe/polycrystalline β-FeSi_<2-x>Ge_x]_n (x=0.5, 0.4, 0.2 for n=1, 2, 4, respectively) multilayered structures were formed. From the analysis of X-ray diffraction spectra, it was found that the lattice constants ofβ-FeSi_<1.5>Ge_<0.5> changed from those of relaxed β-FeSi_2 by 0.4-0.5%. The change decreased with increasing n, which was due to the segregation of Ge atoms from the a-Fe_<0.4>Si_<0.5>Ge_<0.1> layers to the a-Si layers becoming larger with increasing n. After annealing at 800°C, Ge atoms were completely swept out from the β-FeSi_<2-x>Ge_x lattice. In addition, the agglomeration of β-FeSi_2 occurred, and nanocrystals of relaxed β-FeSi_2 and c-Si_<0.7>Ge_<0.3> were formed. This technique for the formation of β-FeSi_<2-x>Ge_x is expected to be useful for energy gap modulation for advanced optoelectrical devices.