Atomic-Scale Physics and Modeling of Schottky Barrier Effect in Carbon Nanotube Nanoelectronics
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Atomic-Scale Physics and Modeling of Schottky Barrier Effect in Carbon Nanotube Nanoelectronics Yongqiang Xue* College of Nanoscale Science and Engineering, University at Albany, State University of New York, Albany, New York 12203 * Email: [email protected]; URL: http://www.albany.edu/~yx152122. ABSTRACT We present an atomistic self-consistent study of the electronic and transport properties of semiconducting carbon nanotubes in contact with metal electrodes at different contact geometries. We analyze the Schottky barrier effect at the metal-nanotube interface by examining the electrostatics, the band line up and the conductance of the metal-nanotube wire-metal junction as a function of the nanotube channel length, which leads to an effective decoupling of interface and bulk effects in electron transport through nanotube junction devices. INTRODUCTION Nanostructured components will undoubtedly play central roles in the development of nextgeneration integrated device technology [1]. A key issue involved in the operation of all such devices is to connect the nanostructured component to the external electrical circuits. Here metallic electrodes are often used, in contrast to conventional semiconductor devices where degenerately doped semiconductors are the typical choice. Understanding the electronic and transport properties through metal-nanostructure interfaces therefore presents a unifying thread and common perspective in nanoelectronics research. Among the nanostructures of current interest, single-wall carbon nanotubes (SWNTs) are rather unique due to their cylindrical geometry, stable lattice structures and diameter/chirality- dependent electronic structure [2]. In addition, it is relatively easy to dope the SWNT, add a third gate terminal and to fabricate SWNT hetero-structures on a single-tube. SWNT-based devices therefore provide a test bed both for exploring novel device technology functioning at the nano/molecular-scale and for examining device physics issues relevant to nanoelectronics research in general. A point of continuing controversy in nanotube devices has been the effect of Schottky barriers at the metal-SWNT interface [2-5]. Since SWNTs are atomic-scale nanostructures in both the transport (axial) and the gating (circumferential) dimensions, any barrier that may form at the metal-SWNT interface has a finite width and a finite thickness. In general, a microscopic model will be needed to account for faithfully the atomistic nature of the electronic processes in SWNT-based devices [6]. The purpose of this paper is thus to present a microscopic analysis of the electronic and transport properties of metal-semiconducting SWNT wire interfaces at different contact geometries, which takes fully into account the atomic-scale electronic structure and the three-dimensional electrostatics of the metal-SWNT-metal junctions. We analyze the Schottky barrier effect at the metal-SWNT interface by examining the electrostatics, the band lineup and the conductance of the metal-SWNT wire-metal as a functi
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