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Published January 9, 2019 | Supplemental Material
Journal Article Open

Anisotropic Quantum Well Electro-Optics in Few-Layer Black Phosphorus

Abstract

The incorporation of electrically tunable materials into photonic structures such as waveguides and metasurfaces enables dynamic, electrical control of light propagation at the nanoscale. Few-layer black phosphorus is a promising material for these applications due to its in-plane anisotropic, quantum well band structure, with a direct band gap that can be tuned from 0.3 to 2 eV with a number of layers and subbands that manifest as additional optical transitions across a wide range of energies. In this Letter, we report an experimental investigation of three different, anisotropic electro-optic mechanisms that allow electrical control of the complex refractive index in few-layer black phosphorus from the mid-infrared to the visible: Pauli-blocking of intersubband optical transitions (the Burstein–Moss effect); the quantum-confined Stark effect; and the modification of quantum well selection rules by a symmetry-breaking, applied electric field. These effects generate near-unity tuning of the BP oscillator strength for some material thicknesses and photon energies, along a single in-plane crystal axis, transforming absorption from highly anisotropic to nearly isotropic. Lastly, the anisotropy of these electro-optical phenomena results in dynamic control of linear dichroism and birefringence, a promising concept for active control of the complex polarization state of light, or propagation direction of surface waves.

Additional Information

© 2018 American Chemical Society. Received: September 25, 2018; Revised: December 5, 2018; Published: December 7, 2018. The authors gratefully acknowledge support from the Department of Energy, Office of Science (DE-FG02-07ER46405) and for facilities of the DOE "Light-Material Interactions in Energy Conversion" Energy Frontier Research Center (DE-SC0001293). W.S.W. also acknowledges support from an NDSEG Graduate Research Fellowship. M.C.S., D.J., and C.M.W. acknowledge fellowship support from the Resnick Institute. J.W. acknowledges support from the National Science Foundation Graduate Research Fellowship (1144469). Author Contributions: M.C.S. and W.S.W contributed equally. The authors declare no competing financial interest.

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