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 im-plantation 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).