Hexagonal SixGe1-xas a direct-gap semiconductor

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Broderick, Christopher A.
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Institute of Electrical and Electronics Engineers (IEEE)
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The band gap of germanium (Ge) is “weakly” indirect, with the L6c conduction band (CB) minimum lying only ≈150meV below the zone-center Γ7c CB edge in energy. This has stimulated significant interest in engineering the band structure of Ge, with the aim of realizing a direct-gap group-IV semiconductor compatible with established complementary metal-oxide-semiconductor fabrication and processing infrastructure. Recent advances in nanowire fabrication now allow growth of Ge in the metastable lonsdaleite (“hexagonal diamond”) phase, reproducibly and with high crystalline quality. In its lonsdaleite allotrope Ge is a direct- and narrow-gap semiconductor, in which the zone-center T8c CB minimum originates via back-folding of the L6c CB minimum of the conventional cubic (diamond) phase. Here, we analyze the electronic structure evolution in direct-gap lonsdaleite SixGe 1-x alloys from first principles, using a combination of alloy supercell calculations and zone unfolding. We confirm the Si composition range x≤ 25 % across which SixGe 1-x possesses a direct band gap, quantify the impact of alloy-induced band hybridization on the inter-band optical matrix elements, and describe qualitatively the consequences of the alloy band structure for carrier recombination.
Band structures , Photonic band gap , Optical device fabrication , Discrete Fourier transforms , Radiative recombination , Diamonds , Germanium
Broderick, Christopher A. (2022) 'Hexagonal SixGe1-xas a direct-gap semiconductor', 2022 IEEE Photonics Society Summer Topicals Meeting Series (SUM), Cabo San Lucas, Mexico, 11-13 July. doi: 10.1109/SUM53465.2022.9858220
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