Sublayer-Enhanced Growth of Highly Ordered Mn₅Ge₃ Thin Film on Si(111)

Mn₅Ge₃ epitaxial thin films previously grown mainly on Ge substrate have been synthesized on Si(111) using the co-deposition of Mn and Ge at a temperature of 390 °C. RMS roughness decreases by almost a factor of two in the transition from a completely polycrystalline to a highly ordered growth mode. This mode has been stabilized by changing the ratio of the Mn and Ge evaporation rate from the stoichiometric in the buffer layer. Highly ordered Mn₅Ge₃ film has two azimuthal crystallite orientations, namely Mn₅Ge₃ (001) [1-10] and Mn₅Ge₃ (001) [010] matching Si(111)[-110]. Lattice parameters derived a (7.112(1) Å) and c (5.027(1) Å) are close to the bulk values. Considering all structural data, we proposed a double buffer layer model suggesting that all layers have identical crystal structure with P6₃/mcm symmetry similar to Mn₅Ge₃, but orientation and level of Si concentration are different, which eliminates 8% lattice mismatch between Si and Mn₅Ge₃ film. Mn₅Ge₃ film on Si(111) demonstrates no difference in magnetic properties compared to other reported films. T_C is about 300 K, which implies no significant excess of Mn or Si doping. It means that the buffer layer not only serves as a platform for the growth of the relaxed Mn₅Ge₃ film, but is also a good diffusion barrier.