Numerical study of quantum transport in the double-gate graphene nanoribbon field effect transistors Hakimeh Mohammadpour a , Asghar Asgari b,c,n a Institute for Advanced studies in Basic Sciences (IASBS), Zanjan, Iran b Research Institute for Applied Physics and Astronomy, University of Tabriz, Tabriz 51665-163, Iran c School of Electrical, Electronic and Computer Engineering; The University of Western Australia, Crawley, WA 6009, Australia article info Article history: Received 30 March 2011 Received in revised form 12 May 2011 Accepted 25 May 2011 Available online 1 June 2011 abstract The ballistic performance of armchair graphene nanoribbon (GNR) field effect transistors (FET) with doped source and drain at different lengths of the channel are studied by self-consistently solving the non-equilibrium Green’s Function (NEGF) transport equation in an atomistic basis set with a 3-D Poisson equation. The I–V characteristics of the simulated model manifests the ballistic top of the barrier and tunneling under the barrier currents in different lengths of the intrinsic channel for two different doping of the source and drain extensions of the device. The length-dependent maximum cut-off frequency is derived. & 2011 Elsevier B.V. All rights reserved. 1. Introduction Today’s transistors being below 100 nm scale have entered the nanoelectronics regime. The shortcomings of the silicon technol- ogy in further scaling down demands an alternative channel material. So, emerging studies have been performing on new research devices; Ge and III–V-based devices are among them [1–6]. In the last decade vast attentions have been dedicated to carbon-based nanostructures like carbon nanotube (CNT) FETs due to their unique electronic properties, especially their very high carrier mobility [3–6]. The electronic properties of CNT depend on its chirality; however, today’s state-of-the-art tech- nology does not provide a straightforward way to control the chirality during growth. Since the discovery of graphene, the two-dimensional sheet of carbon atoms arranged in honeycomb lattice structure, graphene FETs have been widely studied because of their interesting transport properties and potential electronic applications [4–13]. Graphene shares the same unique electronic and physical proper- ties of CNT; exceptionally high carrier mobility. 10,000 cm/Vs of graphene has been experimentally and theoretically demonstrated promising the ballistic graphene-based FETs, which is desirable for high-speed electronic applications [4,9–12]. While its gapless energy-band structure prohibits its usage as the channel material in FETs of high I ON /I OFF ratio, however, the gap can be opened in edge-terminated graphene, so called graphene nanoribbons [13,14]. As in the CNTs, the electronic properties of GNR depend on the channel chirality such that while zigzag graphene nanoribbons are metallic, armchair graphene nanoribbons are either metallic or semiconducting depending on their widths; armchair GNR of width W¼ (3n  1)a 1 (n is an integer, a 1 ¼ 3  the nearest C–C length) is semiconducting and metallic otherwise. The magnitude of the gap scales inversely with the GNR width [14]. The flat structure of graphene along with the advances in the electron and ion beam lithography techniques provides the band- gap engineering by adjusting the width of the nanoribbon. This provides the opportunity of combining metallic and semiconduc- tor nanoribbons on the same substrate using continues graphene sheet so that there is no need to the connecting wires in all- graphene circuits. The ultra-thin structure of graphene, further- more, would provide an extremely good gate-control of the different regions of the circuit. On account of its unique properties, graphene is considered to be among the candidate materials for post-silicon electronics by the International Technology Roadmap for Semiconductors, the strategic planning document for the semiconductor industry. Recently, great progress has been achieved in fabrication of graphene field-effect devices [15,16]. A top–down approach has been used to cut graphene sheets into nanoribbons with widths below 10 nm [17]. Also a bottom-up approach has been used to fabricate the nanoscale graphene FETs [18]. In order to provide an early assessment of the opportunities of functionalized graphene in nanoscale electronics, theoretical and numerical simulations can be very useful to explore the function- ality characteristics of graphene electronic devices. The semiclassical transport model that is coupled to a simple treatment of self-consistent electrostatics has been studied in Ref. [19]. But this model does not capture the quantum tunneling Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physe Physica E 1386-9477/$ - see front matter & 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.physe.2011.05.027 n Corresponding author at: University of Tabriz, Research Institute for Applied Physics and Astronomy, 29 Bahman BLV, Tabriz 51665-163, Iran. Tel.: þ98 411 3393007; fax: þ98 411 3347050. E-mail address: asgari@tabrizu.ac.ir (A. Asgari). Physica E 43 (2011) 1708–1711