Synthesis of relaxed Ge0.9Sn0.1/Ge by nanosecond pulsed laser melting

We present a new approach to the fabrication of fully relaxed Ge1-ySny layers on Ge with Sn concentration y up to 13 at. % The incorporation of Sn in Ge was obtained by sputtering of thin Sn films (< 20 nm) directly on Ge wafers followed by pulsed laser melting in air. Microstructural analyses combining high-resolution transmission electron microscopy, atom probe tomography and nanobeam precession electron diffraction were performed to investigate the Sn distribution and the strain state down to the nanoscale. If y < 6 at. %, Ge1-ySny layers are fully substitutional and fully strained with no or very few extended defects. The formation of Sn-rich regions in correspondence of dislocations is instead observed for y > 6 at. %. However, outside these regions, Ge1-ySny layers present a very homogeneous Sn distribution, full Sn substitutionality, full strain relaxation, and excellent crystalline quality. This new approach could offer, if properly optimized, an alternative to epitaxy or ion implantation to fabricate high quality Ge1-ySny alloys, with the important add-on of the ability of the pulsed laser melting to perform spatially confined thermal processes (both laterally and in depth).