Radiative recombination in GeSn epitaxial architectures

GeSn binary alloys have emerged over the past years as means to overcome the longstanding limitations of group IV materials, in particular in the field of optoelectronics. Epitaxial GeSn layers grown on Ge-buffered Si substrates offer exciting prospects, as evidenced by the very recent demonstration of an optically pumped laser and by the tunable nature of the direct gap [1]. Nevertheless, the low quantum efficiency of such GeSn heterostructures is an unanswered issue with far-reaching consequences from both fundamental and technological perspectives. Here we addressed the impact of strain relaxation on light emission properties of tens-of-nm thick GeSn epitaxial layers with Sn content up to ~10%. An in-depth analysis of the temperature dependence of the integrated photoluminescence intensity is supported by a model of carrier dynamics, which describes the competitive interplay between the radiative band-edge transitions and the trapping of carriers by defects. By doing so, we clarified recent experimental observations and gathered a deeper understanding of radiative recombination processes. By studying the optical properties of GeSn epilayers as a function of strain relaxation we clarify strategies for yielding extremely efficient photonic devices, thus contributing to current worldwide efforts aimed at combining electrical and optical functionalities on a single computer chip. 1. Nature Photon. 9, 88 (2015); PRL 102, 107403 (2009)