Direct bandgap GeSn light emitting diodes for short-wave infrared applications grown on Si

Abstract

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 efficient 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 confirm 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 µm). We have, however, identified some limitations of the GeSn/Ge MQW approach regarding emission efficiency, which can be overcome by introducing SiGeSn ternary alloys as quantum confinement barriers.

(Si)GeSn nanostructures for light emitters

“…The Sn concentration of both the buffer and top GeSn well were varied in the range 0 -at.%, which is experimentally accessible in epitaxial growth 14 . In recent publications we have examined the region where the GeSn well undergoes a transition from indirect to direct bandgap depending on the Sn concentration in the GeSn buffer and well 6,18 . If we exclude the parameter configurations in which the GeSn well has an indirect, the Ge well has a direct bandgap and where the alignment for the bands is not of type I, only a small parameter space is left, suitable for carrier confinement (green area, Figure 3 (b)).…”