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Ratcheting quasi-ballistic electrons in silicon geometric diodes at room temperature

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Science  10 Apr 2020:
Vol. 368, Issue 6487, pp. 177-180
DOI: 10.1126/science.aay8663

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Room-temperature electron ratchets

Conventional diodes rectify current flow by forming a junction between dissimilar conductors; a metal-semiconductor diode that forms a Schottky barrier is one example. In these devices, capacitance limits operating frequency. Custer et al. describe a diode made entirely of silicon that can rectify currents up to 40 gigahertz at room temperature. They fabricated silicon nanowires with a cylindrical sawtooth profile that act as ratchets, funneling current preferentially in one direction through specular reflection of quasi-ballistic electrons.

Science, this issue p. 177

Abstract

Ratcheting effects play an important role in systems ranging from mechanical socket wrenches to biological motor proteins. The underlying principle is to convert a fluctuating, unbiased force into unidirectional motion. Here, we report the ratcheting of electrons at room temperature using a semiconductor nanowire with precisely engineered asymmetry. Modulation of the nanowire diameter creates a cylindrical sawtooth geometry with broken inversion symmetry on a nanometer-length scale. In a two-terminal device, this structure responded as a three-dimensional geometric diode that funnels electrons preferentially in one direction through specular reflection of quasi-ballistic electrons at the nanowire surface. The ratcheting effect causes charge rectification at frequencies exceeding 40 gigahertz, demonstrating the potential for applications such as high-speed data processing and long-wavelength energy harvesting.

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