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 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.