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


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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