No abstract

Highly textured Ge0.91Sn0.09 is obtained on both amorphous SiO2/Si and glass substrates at low temperatures <475 oC, which shows grain sizes up to tens of microns. Strikingly, the nucleation center spacing ranges from 0.1 to 1 mm, orders of magnitude larger than common solid state crystallization. This observation indicates an exceedingly high grain growth rate vs. a low nucleation rate. Therefore, we can control nucleation sites and fabricate geometrically confined pseudo single crystalline GeSn grain using patterning techniques, including surface Sn dots/patches, local laser annealing, and nanotaper patterns. Another remarkable result is that ~9 at.% Sn is incorporated substitutionally into Ge, far exceeding the equilibrium solubility limit of ~1 at.%. The high Sn composition, together with ~0.24% thermally induced tensile strain in the film, shifts the GeSn direct band gap to ~0.5 eV (2500nm) and converts it into a direct band gap semiconductor with significantly enhanced optoelectronic properties.

We report a highly (111)-textured Ge 0.9 Sn 0.1 thin film fabricated on SiO 2 at 464 o C. Incorporating Sn into Ge significantly reduces the crystallization temperature and red-shifts the direct band gap to ~0.5 eV, approaching indirect-to-direct gap transition.