The experimental demonstration of fundamental direct bandgap, group IV GeSn alloys has constituted an important step towards realization of the last missing ingredient for electronic-photonic integrated circuits, i.e. the e cient group IV laser source. In this contribution, we present electroluminescence studies of reduced-pressure CVD grown, direct bandgap GeSn light emitting diodes (LEDs) with Sn contents up to 11 at.%. Besides homojunction GeSn LEDs, complex heterojunction structures, such as GeSn/Ge multi quantum wells (MQWs) have been studied. Structural and compositional investigations con rm high crystalline quality, abrupt interfaces and tailored strain of the grown structures. While also being suitable for light absorption applications, all devices show light emission in a narrow short-wave infrared (SWIR) range. Temperature dependent electroluminescence (EL) clearly indicates a fundamentally direct bandgap in the 11 at.% Sn sample, with room temperature emission at around 0.55 eV (2.25 m). We have, however, identi ed some limitations of the GeSn/Ge MQW approach regarding emission e ciency, which can be overcome by introducing SiGeSn ternary alloys as quantum con nement barriers
