Optical spectroscopy of emission from GeSn waveguides on Si

GeSn alloys are attractive for infrared emission due to the tunable band gap in the infrared and the quasi-direct or direct nature of the gap. Epitaxial growth of GeSn on Si has been demonstrated using multiple growth techniques and is now being incorporated into commercial device fabrication. Recently, laser emission from GeSn waveguides on Si has been demonstrated at temperatures up to 240 K, but the search for room temperature Si-based laser continues. In this work, we investigate the optical emission from optically-pumped GeSn waveguides at room temperature using optical spectroscopy. The results show that there is a highly nonlinear dependence on the total emission output power with respect to the input pump power. However, measurements of the emission spectrum do not show any narrowing of the emission peak, and Fabry-Perot measurements do not show any observable modes. Modeling of spontaneous emission from these materials indicates that the experimental power dependence can only be the result of optical gain in the GeSn. This result shows that optical gain at room temperature is possible.