Voltage-tunable circular photogalvanic effect in silicon nanowires

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Science  14 Aug 2015:
Vol. 349, Issue 6249, pp. 726-729
DOI: 10.1126/science.aac6275

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Chirality from achiral structures

The most common materials used in electronics produce only a simple optical response. Dhara et al. observed a complex circular photogalvanic effect in silicon nanowires, with the magnitude and direction of the induced photocurrent dependent on the polarization of the light. The specifics of the structure and geometry of the component materials are responsible for the effect. It should therefore be possible to engineer the same effect in other achiral materials and thus expand the box of enhanced functional materials for optical applications.

Science, this issue p. 726


Electronic bands in crystals can support nontrivial topological textures arising from 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 the generation of photocurrents whose magnitude and polarity depend on the chirality of optical excitation. We show that the 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 the CPGE. The generation of chirality-dependent photocurrents in silicon with a purely orbital-based mechanism will enable new functionalities in silicon that can be integrated with conventional electronics.

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