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The optoelectronic properties of Ge1−x−ySixSny/Ge1−xSnx/Ge1−x−ySixSny double heterostructures pseudomorphically grown on a Ge substrate were investigated. The photoluminescence (PL) intensity of the sample with Ge0.66Si0.23Sn0.11 cladding layers is three times larger compared to PL from structure with a Ge cladding layer, which can be attributed to higher energy band offsets at both conduction and valence band edges at the Ge0.91Sn0.09/Ge0.66Si0.23Sn0.11 interface. The PL spectrum of the sample with the Ge0.66Si0.23Sn0.11 cladding layer at room temperature can be deconvoluted into four components, and the origins of these components can be assigned to direct and indirect transitions by measuring the temperature dependence of each component’s intensity. In addition, we examined the formation and characterization of strain-relaxed Ge1−x−ySixSny/Ge1−xSnx/Ge1−x−ySixSny double heterostructures to relieve the compressive strain in the Ge1−xSnx layer. Stacking faults were observed in the Ge1−xSnx and Ge1−x−ySixSny layers. The PL peak intensity of the strain-relaxed Ge1−xSnx layer decreases by a factor of 1/20 compared to the PL peak intensity of the double heterostructure pseudomorphically grown on a Ge(001) substrate. In addition, PL intensity can be increased by post-deposition annealing owing to decreasing defects. [ABSTRACT FROM AUTHOR]