Ratcheting Electrons with Silicon Geometric Diodes for Quasi-ballistic Terahertz Rectennas

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Nontechnical Abstract:Diodes are a basic component of electric circuits and are used to control the flow of current. They are vital to the operation of nearly all electronic devices, from laptop computers to cameras. Although diodes have existed for many decades, they typically have limitations in terms of how easy they are to make and how quickly they can operate. In this project, a relatively new type of diode termed a geometric diode will be fabricated and tested. The diodes are relatively simple to fabricate and can potentially operate at very high speeds. To create the diodes, microscopic wires composed of silicon will be grown to have a funnel-like shape. These structures will then be tested for their capacity to funnel current in one direction but not in the opposite, an effect that is similar to a ratchet. The diodes will be progressively tested at higher speeds to determine their ultimate performance limits. Technology derived from the outcomes of this project has potential applications in imaging, data transfer, communications, security screening, and energy harvesting. The project will also train students at multiple grade levels, and the results will be disseminated through publications, conferences, and public outreach events.Technical Abstract:Ballistic rectifiers represent a special class of diode typically fabricated in two-dimensional electron gas systems by designing an asymmetric structure with high-resolution lithography. Two terminal silicon nanowire geometric diodes are an alternate and unconventional strategy to produce electrical diodes capable of high-frequency rectification. The diodes are geometrically-asymmetric nanostructures that operate via a quasi-ballistic mechanism, causing ballistic electrons to be directed through a constriction in the forward direction but to be reflected backwards in the reverse. This asymmetry in the flow of current causes the ratcheting of electrons and generation of a direct current (DC) bias upon application of an alternating current (AC) signal. Most importantly, the ballistic mechanism of operation indicates that these structures can potentially rectify AC signals into the terahertz (THz) regime. Through a combination of experiment and modeling, this project will develop and demonstrate the design principles that govern the performance of nanowire geometric diodes. The diodes will be tested in the THz regime by fabricating single-nanowire rectennas and illuminating with THz radiation. Overall, the studies will reveal fundamental characteristics of nanowire geometric diodes and highlight their potential to serve as a new class of high-frequency rectifier. The effort involves students at multiple levels—from high-school through graduate—with a project that bridges the interface between materials science, physics, and electrical engineering, providing breadth of experience for the students involved.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.