  The precise knowledge of the atomic order in monocrystalline alloys is
fundamental to understand and predict their physical properties. With this
perspective, we utilized laser-assisted atom probe tomography to investigate
the three-dimensional distribution of atoms in non-equilibrium epitaxial
Sn-rich group IV SiGeSn ternary semiconductors. Different atom probe
statistical analysis tools including frequency distribution analysis, partial
radial distribution functions, and nearest neighbor analysis were employed in
order to evaluate and compare the behavior of the three elements to their
spatial distributions in an ideal solid solution. This atomistic-level analysis
provided clear evidence of an unexpected repulsive interaction between Sn and
Si leading to the deviation of Si atoms from the theoretical random
distribution. This departure from an ideal solid solution is supported by first
principal calculations and attributed to the tendency of the system to reduce
its mixing enthalpy throughout the layer-by-layer growth process.
