Formation and characterization of Ge1−x−ySixSny/Ge1−xSnx/Ge1−x−ySixSny double heterostructures with strain-controlled Ge1−x−ySixSny layers

The formation of Ge1−x−ySixSny/Ge1−xSnx/Ge1−x−ySixSny double heterostructures with strain-controlled Ge1−x−ySixSny layers and their crystalline properties were investigated. We achieved the epitaxial growth of double heterostructures consisting of a Ge1−xSnx layer with a Sn content of 9% sandwiched between compressive- or tensile-strained Ge1−x−ySixSny layers. The strain sign of the Ge1−x−ySixSny epitaxial layer influenced the crystallinity of the double heterostructures. Compressive-strained Ge1−x−ySixSny layers provided double heterostructures with higher crystallinity than the tensile-strained ones. The magnitude of strain in the Ge1−x−ySixSny layers also affected the surface roughness of the double heterostructures. Low surface roughness was achieved by decreasing the magnitude of strain in the Ge1−x−ySixSny layers. Moreover, the strain sign and/or Si content in Ge1−x−ySixSny influenced the thermal stability of the double heterostructures. Compressive-strained Ge1−x−ySixSny and/or a low Si content in Ge1−x−ySixSny improved the thermal stability of the double heterostructures to withstand annealing temperatures as high as 400 °C.