Direct bandgap emission from strain-doped germanium

• Published in: Nature communications Vol. 15; no. 1; pp. 618 - 7
• Main Authors: Yuan, Lin-Ding, Li, Shu-Shen, Luo, Jun-Wei
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 19.01.2024; Nature Publishing Group; Nature Portfolio
• Subjects: 119/118; 639/301/1034/1038; 639/301/119/1000; Compatibility; Dipoles; Emission; Emissions; Emitters; Energy gap; Far infrared radiation; First principles; Germanium; Humanities and Social Sciences; Light sources; Lithium; Metal oxide semiconductors; multidisciplinary; Optoelectronics; Rare gases; Science; Science (multidisciplinary); Semiconductors; Silicon; Tensile strain
• ISSN: 2041-1723; 2041-1723
• DOI: 10.1038/s41467-024-44916-w

Germanium (Ge) is an attractive material for Silicon (Si) compatible optoelectronics, but the nature of its indirect bandgap renders it an inefficient light emitter. Drawing inspiration from the significant expansion of Ge volume upon lithiation as a Lithium (Li) ion battery anode, here, we propose incorporating Li atoms into the Ge to cause lattice expansion to achieve the desired tensile strain for a 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 to possess a dipole transition matrix element comparable to that of typical direct bandgap semiconductors. To enhance compatibility with Si Complementary-Metal-Oxide-Semiconductors (CMOS) technology, we additionally suggest implanting noble gas atoms instead of Li atoms. We also demonstrate the tunability of the direct-bandgap emission wavelength through the manipulation of dopant concentration, enabling coverage of the mid-infrared to far-infrared spectrum. This Ge-based light-emitting approach presents exciting prospects for surpassing the physical limitations of Si technology in the field of photonics and calls for experimental proof-of-concept studies. The authors proposed a Silicon technology-compatible approach to convert Germanium from an indirect bandgap to a direct bandgap via doping. This is done to expand the lattice to produce tunable effective tensile strain, aiming towards the on-chip light sources.