Effects of Annealing on the Behavior of Sn in GeSn Alloy and GeSn-Based Photodetectors

Ge $_{{1}-{x}}$ Sn x alloy films with Sn contents of 3% and 10% were grown on Si wafers by low-temperature nonequilibrium molecular beam epitaxy. The thermostabilities of the GeSn films and photodetectors containing them were studied. No Sn segregation was observed in Ge0.97Sn0.03 films annealed below 750 °C. Conversely, Sn segregation occurred and Sn nanoparticles formed within the Ge0.90Sn0.10 films annealed above 400 °C. Upon increasing the annealing temperature to 750 °C, Sn particles were thermally driven and segregated on the surface of both Ge0.97Sn0.03 and Ge0.90Sn0.10 films. Photodetectors were fabricated based on the as-grown and annealed Ge0.90Sn0.10 films. Because of the decreased defect content of the Ge0.90Sn0.10 film after annealing, the dark current of the GeSn photodetectors decreased obviously and the responsivity of the devices increased. These results are fundamentally important for the applications of high-performance photodetectors and lasers based on GeSn alloys.