Dislocation-Related Photoluminescence Emission in MBE-Grown GeSn

This study reports on the observation of photoluminescence (PL) from GeSn alloys grown using a graded Sn approach by molecular beam epitaxy (MBE) and references the resulting PL with that of a typical sample grown by chemical vapor deposition (CVD). The GeSn PL intensity is a factor of about 6 times lower for the MBE-grown sample. The MBE sample exhibited multiple PL emission features, with a dominant emission at about 0.51 eV, which our analysis links to dislocation-induced trap states originating in the Ge substrate and Ge buffer layer. These defects propagate into the GeSn and capture excited carriers, reducing the overall PL efficiency. High-resolution transmission electron microscopy confirmed dislocation concentrations near the surface of the MBE sample, correlating with the observed defect-related emissions. In contrast, the CVD sample displayed a single PL emission (∼0.57 eV), indicating fewer defect states and more efficient carrier recombination. The strong influence of dislocations on the MBE sample’s optical properties emphasizes the importance of minimizing defect states in the Ge substrate and buffer to improve PL performance in GeSn alloys. These findings indicate that the corresponding dislocation-induced defects are a key factor limiting reports of PL from MBE-grown GeSn alloys.