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

Abstract

We investigated the photoluminescence (PL) properties of heavily Sb doped Ge_1−xSn_x layer and demonstrated the formation of double heterostructure (DHS) for Ge_1−xSn_x active layer. First, we found that a single PL peak is observed for Ge_1−xSn_x layers thicker than 80 nm with increasing Sb doping concentration up to 10²⁰ cm⁻³, which is attributed by superior crystallinity and pseudo direct transition mechanism, while the 15-nm-thick Ge_1−xSn_x layer did not show PL signal. Next, a favorable heterostructure for Ge_1−xSn_x was proposed from the viewpoint of increasing valence band offset (ΔE_v) using n-Si_yGe_1−y as clad layer. We demonstrated the formation of n-Si_yGe_1−y(15 nm)/n⁺-Ge_1−xSn_x(15 nm)/n-Si_yGe_1−y(15 nm) DHS with superior crystallinity and a strong PL peak intensity comparable to the thick Ge_1−xSn_x. Finally, we discussed reasons for the PL performance improvement by forming the DHS, which would be due to the sufficient carrier confinement and the suppression of surface recombination.