Combining Axial and Radial Nanowire Heterostructures: Radial Esaki Diodes and Tunnel Field-Effect Transistors

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Abstract
The ever-growing demand on high-performance electronics has generated transistors with very impressive figures of merit (Radosavljevic et al., IEEE Int. Devices Meeting 2009, 1–4 and Cho et al., IEEE Int. Devices Meeting 2011, 15.1.1–15.1.4). The continued scaling of the supply voltage of field-effect transistors, such as tunnel field-effect transistors (TFETs), requires the implementation of advanced transistor architectures including FinFETs and nanowire devices. Moreover, integration of novel materials with high electron mobilities, such as III–V semiconductors and graphene, are also being considered to further enhance the device properties (del Alamo, Nature2011, 479, 317–323, and Liao et al., Nature2010, 467, 305–308). In nanowire devices, boosting the drive current at a fixed supply voltage or maintaining a constant drive current at a reduced supply voltage may be achieved by increasing the cross-sectional area of a device, however at the cost of deteriorated electrostatics. A gate-all-around nanowire device architecture is the most favorable electrostatic configuration to suppress short channel effects; however, the arrangement of arrays of parallel vertical nanowires to address the drive current predicament will require additional chip area. The use of a core–shell nanowire with a radial heterojunction in a transistor architecture provides an attractive means to address the drive current issue without compromising neither chip area nor device electrostatics. In addition to design advantages of a radial transistor architecture, we in this work illustrate the benefit in terms of drive current per unit chip area and compare the experimental data for axial GaSb/InAs Esaki diodes and TFETs to their radial counterparts and normalize the electrical data to the largest cross-sectional area of the nanowire, i.e. the occupied chip area, assuming a vertical device geometry. Our data on lateral devices show that radial Esaki diodes deliver almost 7 times higher peak current, Jpeak = 2310 kA/cm2, than the maximum peak current of axial GaSb/InAs(Sb) Esaki diodes per unit chip area. The radial TFETs also deliver high peak current densities Jpeak = 1210 kA/cm2, while their axial counterparts at most carry Jpeak = 77 kA/cm2, normalized to the largest cross-sectional area of the nanowire.

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