Graphene quantumwise
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Moreover, these devices may also be interconnected within the same single Graphene monolayer using GNRs 37, which may lead to not only atomically-thin devices, but more interestingly, all-Graphene atomically-thin electronic circuits. This would mean that, within a single Graphene monolayer, metallic and semiconducting regions can be formed and a number of planar atomically-thin 2D devices have been proposed based on this concept 35, 36. Etching GNRs with smooth edges 24, 25, 26, 27, 28, 29, 30 or realizing them through other means 31, 32, 33, 34 has been making good progress in recent years and this can lead to the ability of making zGNRs and aGNRs from a single Graphene monolayer. Graphene Nanoribbons, which are long narrow strips of Graphene, can be either zigzag-edged or armchair-edged and can behave as metallic or semiconducting respectively 23. Until recently there was no single material that could have metallic regions and also semiconducting regions within the same plane, until the discovery of Graphene Nanoribbons (GNRs) 21, 22. Nevertheless, these devices suffer from the constraint of not having a metallic gate, as the channel (the nanowire) and the side gates in them need to be made from the same material, which is usually a semiconductor. Self-switching diodes are two-dimensional (2D) planar devices that require very minimal lithography steps during fabrication and are very well suited for a two dimensional material like Graphene. Self-Switching Diodes showed excellent high frequency performance at 110 GHz 19 and were later demonstrated as room-temperature Terahertz detectors 20. A SSD is an asymmetrical nanowire in which rectification occurs due to a self-induced field-effect that enhances conduction through the nanowire in one direction, while suppressing it in the opposite direction.
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In order to overcome this problem diodes based on new rectification mechanisms were proposed, one of which was the Self-Switching Diode (SSD) 18. The nano-scale alternative to a schottky diode would be a diode-connected FET, but this extra diode connection introduces increased parasitic capacitances and inductances that limit the operation frequency of the diode-connected FET. Graphene-based schottky diodes, in which Graphene was used as the metal 14, 15, 16 or the semiconductor 17, have been realized, but are limited to large sizes for high frequency operation.
![graphene quantumwise graphene quantumwise](https://www.mdpi.com/sensors/sensors-19-02731/article_deploy/html/images/sensors-19-02731-g001-550.jpg)
High performance diodes will enable next generation terahertz detectors and new RF systems, but their realization at the nano-scale with high operation frequency has been a challenge. On the other hand, realization of Graphene-based diodes has received much less attention. More recently, new classes of devices have been realized by exploiting some of Graphene's unique properties 12, 13. The realization of high frequency Graphene FETs 5, 6, 7, 8 has led to the realization of wafer scale Graphene integrated circuits 9 with FETs that have enhanced functionalities 10, 11. Graphene, an atomically-thin sheet of carbon atoms 1, has opened many opportunities in the field of electronics due to its unique electronic properties 2, 3 including enhanced performance electronics and sensors 4. Quantum mechanical simulation results, based on the Extended Huckel method and Nonequilibrium Green's Function Formalism, show that a Graphene Self-Switching MISFED with a channel as short as 5 nm can achieve forward-to-reverse current rectification ratios exceeding 5000. The presented devices exhibit excellent current-voltage characteristics while occupying an ultra-small area with sub-10 nm dimensions and an ultimate thinness of a single atom. Based on this concept, we present a new class of nano-scale planar devices named Graphene Self-Switching MISFEDs (Metal-Insulator-Semiconductor Field-Effect Diodes), in which Graphene is used as the metal and the semiconductor concurrently. This property allows metallic and semiconducting regions within a single Graphene monolayer, which can be used in realising two-dimensional (2D) planar Metal-Insulator-Semiconductor field effect devices. By varying the width of these nanoribbons this band gap can be tuned from semiconducting to metallic. Graphene normally behaves as a semimetal because it lacks a bandgap, but when it is patterned into nanoribbons a bandgap can be introduced.