The interplay between strain, Sn content, and temperature on spatially‐dependent bandgap in Ge_1‐xSn_x microdisks

Germanium‐tin microdisks are promising structures for CMOS‐compatible lasing. Their emission properties depend on Sn concentration, strain, and operating temperature. Critically, the band structure of the alloy varies along the disk due to the different lattice deformation associated with the mechanical constraints in the microstructures. We report an experimental and numerical study of Ge 1‐x Sn x microdisk with Sn concentration between 8.5 and 14 at.%. Combining finite element method calculations, micro‐Raman spectroscopy and X‐ray diffraction spectroscopy enables a comprehensive understanding of mechanical deformation, where computational predictions are experimentally validated, leading to a robust model and insight into the strain landscape. Through micro‐photo‐luminescence experiments, the temperature dependence of the band gap of Ge 1‐x Sn x is parametrized using the Varshni formula with respect to strain and Sn content. These results are the input for a spatially‐dependent band structure calculation based on the deformation potential theory. We observe that Sn content and temperature have comparable effects on the bandgap, yielding a decrease of more than 20 meV for an increase of 1 at.% or 100 K, respectively. We also find that the strain gradient impacts the band structure in the whole volume of the microdisk. These findings correlate structural properties to the emission wavelength and spectral width of Ge 1‐x Sn x microdisk lasers, thus demonstrating the importance of material‐related consideration on the design of optoelectronic microstructures. This article is protected by copyright. All rights reserved.