Dislocation-related photoluminescence of GeSn films grown on Ge (001) substrates by molecular beam epitaxy

This paper reports the dislocation-related photoluminescence (PL) in GeSn films The GeSn film samples with Sn content of 1%-7.4% were grown on Ge (001) substrates by molecular beam epitaxy at low temperatures. Dislocations at the interface between the GeSn and the Ge buffer layer as well as the threading dislocations throughout the GeSn layer were observed for the annealed samples, but not for the as-grown samples. PL peaks of the annealed GeSn film samples show a significant red shift with increasing Sn content. However, a large energy difference (122 meV) between the PL peak energy and theoretically calculated indirect bandgap energy was found for all the GeSn films with different Sn contents. Furthermore, the PL peak position as a function of temperature could be well fitted by the calculated E g -T line, indicating that the PL observed in the GeSn films is dislocation-related PL.