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.
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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.
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© 2026, the Authors. Published by the American Physical Society.
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
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