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Photoluminescence properties of heavily Sb doped Ge1−x Sn x and heterostructure design favorable for n+-Ge1−x Sn x active layer

We investigated the photoluminescence (PL) properties of heavily Sb doped n+-Ge1−x Sn x layers and demonstrated the formation of a double heterostructure (DHS) for the n+-Ge1−x Sn x active layer. A single PL peak was observed for n+-Ge1−x Sn x layers thicker than 80 nm with increasing the Sb concentration up to 1020 cm−3, attributed to the superior crystallinity and pseudo-direct bandgap transition mechanism, while a 15 nm thick n+-Ge1−x Sn x layer did not exhibit PL signals. A favorable heterostructure for n+-Ge1−x Sn x is proposed from the viewpoint of the increased valence band offset (ΔE v) using n-Si y Ge1−y as the cladding layer. We demonstrated the formation of an n-Si y Ge1−y (15 nm)/n+-Ge1−x Sn x (15 nm)/n-Si y Ge1−y (15 nm) DHS with a superior crystallinity and high PL peak intensity comparable to that of a thick n+-Ge1−x Sn x . We discuss the reasons for the PL performance improvement by forming the DHS, including the sufficient carrier confinement and the suppression of surface recombination.