Voltage-tunable circular photogalvanic effect in silicon nanowires

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Science  23 Jul 2015:
DOI: 10.1126/science.aac6275

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Electronic bands in crystals can support nontrivial topological textures arising from the spin-orbit interactions but purely orbital mechanisms can realize closely related dynamics without breaking spin degeneracies opening up applications in materials containing only light elements. One such application is the circular photogalvanic effect (CPGE), which is generation of photocurrent whose magnitude and polarity depends on chirality of optical excitation. We show that CPGE can arise from interband transitions at the metal contacts to silicon nanowires where inversion symmetry is locally broken by an electric field. Bias voltage that modulates this field, further controls the sign and magnitude of CPGE. The generation of chirality-dependent photocurrents in silicon with a purely orbital-based mechanism will enable new functionalities in Si that can be integrated with conventional electronics.

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