Nature of the band gap of Ge:C alloys: insights from hybrid functional density functional theory calculations

Previous studies have shown that incorporating a small fraction of carbon (C) into germanium (Ge) leads to the lowest conduction state being at the Γ point in small supercell calculations, suggesting that C incorporation can turn Ge into a direct gap semiconductor. We use hybrid functional density f...

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Bibliographic Details
Published in:Semiconductor science and technology 2019-07, Vol.34 (7), p.75007
Main Authors: Kirwan, Amy C, Schulz, Stefan, O'Reilly, Eoin P
Format: Article
Language:English
Subjects:
DFT
Ge:C
group IV alloys
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Summary:Previous studies have shown that incorporating a small fraction of carbon (C) into germanium (Ge) leads to the lowest conduction state being at the Γ point in small supercell calculations, suggesting that C incorporation can turn Ge into a direct gap semiconductor. We use hybrid functional density functional theory calculations as a function of hydrostatic pressure to investigate the nature (Γ-, X- or L-like) of the lowest conduction states in Ge127C1 and Ge63C1 supercells. We find in both cases that the lowest conduction state, at Γ in the supercell, has primarily L-like character. Surprisingly, the Ge Γ state mixes with a higher-lying X state, but has almost no interaction with the L-like conduction band edge state. We conclude that the band gap of the here studied Ge:C systems is therefore only quasi-direct, limiting the benefit of this material system for optoelectronic device applications.
ISSN:0268-1242
1361-6641
DOI:10.1088/1361-6641/ab23a4