Structural, electronic, and optical properties of hexagonal GeSn from density functional theory
Abstract
Unlike cubic GeSn, which undergoes an indirect-to-direct bandgap transition only above a finite Sn concentration, 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-Ge1−xSnx random alloys in the dilute Sn regime (x ≤ 0.10). Substitutional 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 the semiconducting alloy configurations retain a direct bandgap at the Γ point, with a moderate, nearly linear reduction of the bandgap in the dilute regime that shifts the fundamental absorption edge toward the mid-infrared. As the gap approaches zero, its calculated value becomes increasingly sensitive to the atomic configuration and supercell size. Evaluation of the optical transition matrix elements shows that the polarization anisotropy characteristic of pristine 2H-Ge remains observable under dilute Sn alloying. Although alloy disorder relaxes the crystal selection rules, the band edge response remains dominated by light polarized perpendicular to the crystal c axis, whereas the parallel component remains weaker. These results identify dilute hexagonal GeSn as a tunable direct-gap system with a strongly polarization-dependent optical response in the infrared.
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BibTeX
@misc{pulcu2026structural,
title = {{Structural, electronic, and optical properties of hexagonal GeSn from density functional theory}},
author = {Yetkin Pulcu and János Koltai and Andor Kormányos and Guido Burkard},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2605.13166},
eprint = {2605.13166},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2605.13166},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Structural, electronic, and optical properties of hexagonal GeSn from density functional theory
AU - Yetkin Pulcu
AU - János Koltai
AU - Andor Kormányos
AU - Guido Burkard
PY - 2026
DA - 2026/09/21
PB - arXiv
DO - 10.48550/arxiv.2605.13166
UR - https://arxiv.org/abs/2605.13166
AB - Unlike cubic GeSn, which undergoes an indirect-to-direct bandgap transition only above a finite Sn concentration, 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−xSn_x random alloys in the dilute Sn regime (x ≤ 0.10). Substitutional 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 the semiconducting alloy configurations retain a direct bandgap at the Γ point, with a moderate, nearly linear reduction of the bandgap in the dilute regime that shifts the fundamental absorption edge toward the mid-infrared. As the gap approaches zero, its calculated value becomes increasingly sensitive to the atomic configuration and supercell size. Evaluation of the optical transition matrix elements shows that the polarization anisotropy characteristic of pristine 2H-Ge remains observable under dilute Sn alloying. Although alloy disorder relaxes the crystal selection rules, the band edge response remains dominated by light polarized perpendicular to the crystal c axis, whereas the parallel component remains weaker. These results identify dilute hexagonal GeSn as a tunable direct-gap system with a strongly polarization-dependent optical response in the infrared.
ER -