First-principles theory of direct-gap optical emission in hexagonal Ge and its enhancement via strain engineering
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Date
2026-04-21
Authors
Broderick, Christopher A.
Zhang, Xie
Turiansky, Mark E.
Van de Walle, Chris G.
Journal Title
Journal ISSN
Volume Title
Publisher
American Physical Society
Published Version
Abstract
The emergence of hexagonal Ge (2H-Ge) as a candidate direct-gap group-IV semiconductor for Si photonics mandates a rigorous understanding of its optoelectronic properties. Theoretical predictions of a “pseudodirect” band gap, characterized by weak oscillator strength, contrast with a claimed high radiative recombination coefficient B comparable to conventional (cubic) InAs. We compute B in 2H-Ge from first principles and quantify its dependence on temperature, carrier density, and strain. For unstrained 2H-Ge, our calculated spontaneous emission spectra corroborate that measured photoluminescence corresponds to direct-gap emission, but with B being approximately three orders of magnitude lower than in InAs. We confirm a pseudodirect-to-direct-gap transition under ∼2% [0001] uniaxial tension, which can enhance B by up to 3 orders of magnitude, making it comparable to that of InAs. Beyond quantifying the strong enhancement of B via strain engineering, our analysis suggests the dominance of additional, as-yet unquantified recombination mechanisms in this nascent material.
Description
Keywords
Arsenic compounds , Emission spectroscopy , Energy gap , First-principle theory , Gallium phosphide , Germanium compounds , Group-IV semiconductors , III-V semiconductors , InAs , Narrow band gap semiconductors , Optical emissions , Optoelectronics property , Oscillator strengths , Radiative recombination , Recombination coefficient , Si photonics , Spontaneous emission , Strain engineering , [Physics]
Citation
Broderick, C A, Zhang, X, Turiansky, M E & Van de Walle, C G 2026, 'First-principles theory of direct-gap optical emission in hexagonal Ge and its enhancement via strain engineering', Physical Review Materials, vol. 10, no. 4, 044603, pp. 1-8. https://doi.org/10.1103/4m4m-84p3