Growth condition dependence of Ge-doped β-FeSi2 epitaxial film by molecular beam epitaxy

► Ge-doped β-FeSi2 epitaxial films on Si(1 1 1) substrates were grown by molecular beam epitaxy. ► The optimized growth temperature (Ts) and Si/Fe flux ratio were Ts=500 °C and Si/Fe=0.5. ► The lattice constant and the direct transition energy shifted with Ge concentration. ► These results revealed the successful growth of β-Fe(Si1−xGex)2 epitaxial films.