Growth of SiGe/beta-FeSi2 superstructures by annealing of a-Si/a-FeSiGe layered structures was investigated for control of the strains in beta-FeSi2 by Ge doping. The [a-SiGe/beta-FeSi2(Ge)](n) multi-layered structures were formed after annealing at 700 degreesC. From the analysis of the Xray diffraction (XRD) spectra, it was found that beta-FeSi2(Ge) was strained by 0.4-0.5% for the sample with n=l. The strains decreased with increasing n, which was due to that the segregation of the Ge atoms from the a-Fe0.4Si0.5Ge0.1 layers to the a-Si layers became large with increasing n. After annealing at 800 degreesC, agglomeration of beta-FeSi2 occurred, and nanocrystals of relaxed beta-FeSi2 and c-Si0.7Ge0.3 were formed. These demonstrate that the SiGe/beta-FeSi2 superstructures were formed by the Ge segregation. These new structures are useful for formation of opto-electrical devices. (C) 2004 Elsevier B.V. All rights reserved.