D'Avezac, M; Luo, J-W; Chanier, T; Zunger, A; (2012) Genetic-algorithm discovery of a direct-gap and optically allowed superstructure from indirect-gap Si and Ge semiconductors. Physical Review Letters , 108 (2) , Article 027401. 10.1103/PhysRevLett.108.027401.

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Abstract

Combining two indirect-gap materials-with different electronic and optical gaps-to create a direct gap material represents an ongoing theoretical challenge with potentially rewarding practical implications, such as optoelectronics integration on a single wafer. We provide an unexpected solution to this classic problem, by spatially melding two indirect-gap materials (Si and Ge) into one strongly dipole-allowed direct-gap material. We leverage a combination of genetic algorithms with a pseudopotential Hamiltonian to search through the astronomic number of variants of Si /Ge /.../Si /Ge superstructures grown on (001) Si Ge . The search reveals a robust configurational motif-SiGe Si Ge SiGe on (001) Si Ge substrate (x≤0.4) presenting a direct and dipole-allowed gap resulting from an enhanced Γ-X coupling at the band edges. © 2012 American Physical Society.

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