{"paper":{"title":"Structural, electronic, and optical properties of hexagonal GeSn from density functional theory","license":"http://creativecommons.org/licenses/by/4.0/","headline":"2H-Ge1-xSnx alloys keep a direct bandgap at the Gamma point for all dilute tin levels, with strong bowing and giant polarization anisotropy.","cross_cats":[],"primary_cat":"cond-mat.mtrl-sci","authors_text":"Andor Korm\\'anyos, Guido Burkard, J\\'anos Koltai, Yetkin Pulcu","submitted_at":"2026-05-13T08:28:55Z","abstract_excerpt":"Unlike cubic GeSn, which requires a high Sn concentration to undergo an indirect-to-direct bandgap transition, lonsdaleite (2H) germanium is an intrinsic direct-gap semiconductor. We employ first-principles density functional theory to investigate the structural, electronic, and optical properties of 2H-Ge$_{1-x}$Sn$_{x}$ random alloys in the dilute Sn regime ($x \\le 0.10$). The extended alloy disorder is modeled using 48-atom special quasirandom structure (SQS) supercells, and the coherent effective band structure is recovered via spectral band unfolding. We show that 2H-Ge$_{1-x}$Sn$_{x}$ ma"},"claims":{"count":4,"items":[{"kind":"strongest_claim","text":"We show that 2H-Ge_{1-x}Sn_{x} maintains a direct bandgap at the Γ point across the studied composition range, exhibiting a strong bandgap bowing that shifts the fundamental absorption edge into the mid-infrared. Evaluation of the optical transition matrix elements reveals a giant polarization anisotropy dictated by spin-orbit coupling.","source":"verdict.strongest_claim","status":"machine_extracted","claim_id":"C1","attestation":"unclaimed"},{"kind":"weakest_assumption","text":"The assumption that standard density functional theory functionals and 48-atom special quasirandom structure supercells accurately capture the bandgap bowing, optical matrix elements, and disorder effects in the random alloy without significant errors from the chosen exchange-correlation approximation.","source":"verdict.weakest_assumption","status":"machine_extracted","claim_id":"C2","attestation":"unclaimed"},{"kind":"one_line_summary","text":"Hexagonal Ge1-xSnx alloys maintain a direct bandgap at Gamma with strong bowing and robust polarization anisotropy in the dilute Sn regime.","source":"verdict.one_line_summary","status":"machine_extracted","claim_id":"C3","attestation":"unclaimed"},{"kind":"headline","text":"2H-Ge1-xSnx alloys keep a direct bandgap at the Gamma point for all dilute tin levels, with strong bowing and giant polarization anisotropy.","source":"verdict.pith_extraction.headline","status":"machine_extracted","claim_id":"C4","attestation":"unclaimed"}],"snapshot_sha256":"9d8e2dffe534629aa1f60c8a618eca8ab37c0d9aada8926ae7637943301659ca"},"source":{"id":"2605.13166","kind":"arxiv","version":1},"verdict":{"id":"1aeccc29-2ec5-4b26-a316-2ce69ab29c6d","model_set":{"reader":"grok-4.3"},"created_at":"2026-05-14T17:36:43.213808Z","strongest_claim":"We show that 2H-Ge_{1-x}Sn_{x} maintains a direct bandgap at the Γ point across the studied composition range, exhibiting a strong bandgap bowing that shifts the fundamental absorption edge into the mid-infrared. Evaluation of the optical transition matrix elements reveals a giant polarization anisotropy dictated by spin-orbit coupling.","one_line_summary":"Hexagonal Ge1-xSnx alloys maintain a direct bandgap at Gamma with strong bowing and robust polarization anisotropy in the dilute Sn regime.","pipeline_version":"pith-pipeline@v0.9.0","weakest_assumption":"The assumption that standard density functional theory functionals and 48-atom special quasirandom structure supercells accurately capture the bandgap bowing, optical matrix elements, and disorder effects in the random alloy without significant errors from the chosen exchange-correlation approximation.","pith_extraction_headline":"2H-Ge1-xSnx alloys keep a direct bandgap at the Gamma point for all dilute tin levels, with strong bowing and giant polarization anisotropy."},"references":{"count":49,"sample":[{"doi":"","year":null,"title":"Based on this model, our calculations yield a crystal-field 4 A M L1.0 0.5 0.0 0.5 1.0 1.5 Energy (eV) 2H-Ge Ge0.9375Sn0.0625 0.0 0.2 0.4 0.6 0.8 1.0 Spectral Weight Figure 3","work_id":"e7b3c528-4bcb-4df2-960d-02cf9b22d2dd","ref_index":1,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2006,"title":"Soref, The past, present, and future of silicon photon- ics, IEEE Journal of Selected Topics in Quantum Elec- tronics12, 1678 (2006)","work_id":"5e771b10-d830-49bd-a0b7-f27df1fb4cc5","ref_index":2,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2009,"title":"D. A. Miller, Device requirements for optical intercon- nects to silicon chips, Proceedings of the IEEE97, 1166 (2009)","work_id":"6e043508-e1a1-46ca-a3de-1c142484314c","ref_index":3,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2018,"title":"A. H. Atabaki, S. Moazeni, F. Pavanello, H. Gevorgyan, J. Notaros, L. Alloatti, M. T. Wade, C. Sun, S. A. Kruger, H. Meng,et al., Integrating photonics with sil- icon nanoelectronics for the next gene","work_id":"7a1f65b9-61a0-453f-b7ba-30dbc68f7898","ref_index":4,"cited_arxiv_id":"","is_internal_anchor":false},{"doi":"","year":2022,"title":"Y. Han, H. Park, J. E. Bowers, and K. M. Lau, Recent advances in light sources on silicon, Advances in Optics and Photonics14, 404 (2022)","work_id":"bc87ca00-074d-4226-aa95-483404284948","ref_index":5,"cited_arxiv_id":"","is_internal_anchor":false}],"resolved_work":49,"snapshot_sha256":"4ac54d043296eee7e348646ae29cec6a50278ab169c3af0fd5f5ade242b98f4f","internal_anchors":0},"formal_canon":{"evidence_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"author_claims":{"count":0,"strong_count":0,"snapshot_sha256":"258153158e38e3291e3d48162225fcdb2d5a3ed65a07baac614ab91432fd4f57"},"builder_version":"pith-number-builder-2026-05-17-v1"}