Sn-Segregation Behavior and Its Suppression in Ge _{1– <i>y</i>} Sn _<i>y</i> Semiconductor Alloys with <i>y</i> &gt; 0.20

This work presents an investigation of Sn segregation and its suppression in Ge1–ySny semiconductor alloys with ultrahigh Sn content (>20%), which span a technologically important segment of the optical spectrum (4–8 μm) overlapping the MWIR and the molecular fingerprint ranges. Films were grown under conditions that leave temperature as the main parameter that controls Sn-segregation, and comprehensive structural and morphological analyses were conducted to monitor phase separation during epitaxial growth of crystals. These studies specifically address the critical issue of phase stability by focusing on the suppression of Sn clustering, a persistent challenge in the fabrication of supersaturated alloys. Epitaxially stabilized single-phase alloys were obtained at optimized growth temperatures. The high-quality of these samples enabled detailed optical studies that demonstrate band gaps as low as 0.2 eV, suggesting a path for the fabrication of devices covering the entire MWIR range and beyond.