We have investigated the growth condition of Ge-doped beta-FeSi2 on Si(1 1 1) substrates by molecular beam epitaxy (MBE). By the optimization of growth temperature (T-s) and Si/Fe flux ratio, the beta-Fe(Si1-xGex)(2) with a flat surface was grown at T-s=500 degrees C and Si/Fe=0.5, which were different from the optimized condition of the undoped beta-FeSi2 (T-s=670 degrees C, Si/Fe=2.0). In the dependence of lattice constants on Ge concentration, all the lattice constants expanded in the range of x=0-11%. In the direct transition energies (E-g) measured by photoreflectance measurements, the E-g decreased with the increase of Ge concentration. These results revealed that beta-Fe(Si1-xGex)(2) was successfully grown on Si(1 1 1) substrate in the range of x=0-11%. (c) 2012 Elsevier B.V. All rights reserved.