EXAFS sheds light on short-range ordering in G e 1 − x S n x heteroepitaxial layers grown by MBE and CVD

The local arrangement of atoms in an alloy impacts its electronic band structure and, consequently, itsfundamental physical properties. This work investigates the short-range order of tin atoms in binary Ge1−xSnxsemiconductors epitaxially grown on Ge-buffered Si (001) substrates. Samples featuring Sn content up to 13at.% were analyzed by x-ray absorption fine structure spectroscopy at the Sn-K edge. The study reveals howthe growth method and its process parameters, like temperature, or the epitaxial built-up strain affect the localatomic ordering of tin within the alloys. While the deposition technique seems to have a marginal effect on theSn short-range ordering, the growth temperature and Sn content systematically influence the bonding angles Sn.Ge-Sn next neighbor coordination shells, whereas the interatomic distances remain largely unaffected. In the firstcoordination shell Sn-Ge are strongly favored over Sn-Sn, while the opposite happens in the next coordinationshell, where Sn-Sn are systematically favored. These insights into the relationship of growth condition and layerproperties enable to identify the nature of the large variety of electronic and optical properties measured inGe1−xSnx layers.