We demonstrated the simultaneous vertical integration of self contacting and highly oriented nanowires (NWs) into airbridge structures which have been developed into surround gated metal oxide semiconductor field effect transistors (MOSFET). With the use of conventional photolithography, reactive ion etching (RIE) and low pressure chemical vapour deposition a suspended vertical NW architecture is formed on a silicon on insulator (SOI) substrate where the nanodevice will later be fabricated on. The vapour-liquid-solid (VLS) grown Si-NWs are contacted to prepatterned airbridges by a self aligned process and there is no need for post-growth NW assembly or alignment. Such vertical NW architecture can be easily integrated into existing ICs processes opening the path to a new generation of nonconventional nano devices. To demonstrate the potential of this method surround gated vertical MOSFETs have been fabricated with a highly simplified integration scheme combining top-down and bottom-up approaches, but in the same way one can think about the realization of integrated nano sensors on the industrial scale.

The combined capabilities of both a non-planar design and non-conventional carrier injection mechanisms are subject to recent scientific investigations to overcome the limitations of silicon MOSFETs. In this letter we present a multi-mode FET device using silicon nanowires that feature an axial n-type/intrinsic doping junction. A heterostructural device design is achieved by employing a self-aligned nickel-silicide source contact. The polymorph operation of the dual-gate device enabling the configuration of one p- and two n-type transistor modes is demonstrated. Not only the type but also the carrier injection mode can be altered by appropriate biasing of the two gate terminals or by inverting the drain bias. With a combined band-to-band and Schottky tunneling mechanism, in p-type mode a subthreshold swing as low as 143 mV/dec and an ON/OFF ratio of up to 104 is found. As the device operates in forward bias, a non-conventional tunneling transistor is realized, enabling an effective suppression of ambipolarity. Depending on the drain bias, two different n-type modes are distinguishable. The carrier injection is dominated by thermionic emission in forward bias with a maximum ON/OFF ratio of up to 107 whereas in reverse bias a Schottky tunneling mechanism dominates the carrier transport.
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