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

Ge _1-x Snx 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 Ge _0.97 Sn _0.03 films annealed below 750 °C. Conversely, Sn segregation occurred and Sn nanoparticles formed within the Ge _0.90 Sn _0.10 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 Ge _0.97 Sn _0.03 and Ge _0.90 Sn _0.10 films. Photodetectors were fabricated based on the as-grown and annealed Ge _0.90 Sn _0.10 films. Because of the decreased defect content of the Ge _0.90 Sn _0.10 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.