Direct integration of active Ge1-x (Si₄ Sn)_x semiconductors on Si(100)

Doped and intrinsic Ge1-x-y Si_x Sn_y alloys are synthesized directly on Si(100) using simple deposition chemistries and their optical and electrical properties are determined. Tuning the Si/Sn ratio at ∼4 yields strain-free films with Ge-like cell dimensions, while variation of the ratio around this value produces compressively strained, tetragonal structures with an in-plane lattice constant "pinned" to a value close to that of pure Ge (5.658 Å). First-principles calculations show that mixing entropy thermodynamically stabilizes SiGeSn in contrast to GeSn analogs with the same Sn content. GeSn and SiGeSn are predicted to become metastable for 2% and 12% Sn, respectively, in good agreement with experiment.