Direct bandgap emission from strain-doped germanium

Abstract Drawing inspiration from the significant expansion of Ge volume upon lithiation as a Li-ion battery anode, here, we propose to incorporate Li atoms into the Ge lattice to achieve the desired tensile strain for the transition from an indirect to a direct bandgap. Our first-principles calculations show that a minimal amount of 3 at.% Li can convert Ge from an indirect to a direct bandgap, exhibiting a dipole matrix element comparable to that of typical direct bandgap semiconductors. To enhance compatibility with CMOS technology, we additionally suggest implanting noble gas atoms. We also demonstrate the tunability of the direct-bandgap emission wavelength, enabling coverage of the mid-infrared to far-infrared spectrum through the manipulation of dopant concentration. This novel Si-based light-emitting approach presents exciting prospects for surpassing the physical limitations of silicon technology in the field of photonics.