Program

O.12 -- Oral, NCTP-42

Date: Tuesday, 1 August 2017

Time: 14h30 - 14h50

Theoretical study of electronic and thermoelectric nanodevices based on strained graphene junctions

M. Chung Nguyen (1,2,3), V. Hung Nguyen (1,2), H. Viet Nguyen (1) and P. Dollfus (2)

(1) Center for Computational Physics, Institute of Physics, VAST, Hanoi, Vietnam; (2) Institut d’Electronique Fondamentale, Université Paris Sud, Orsay, France; (3) Energy deparment, University of Science and Technology of Hanoi, Vietnam

Graphene, due to its outstanding physical properties, is expected to be able to replace or, at least, complement traditional semiconductors in device technology [1]. However, applications of graphene in electronic devices are still questionable because of its gapless character. In particular, regarding electronic applications, the absence of energy bandgap in the electronic band structure makes it difficult to switch off the current in graphene devices like transistors [2]. For thermoelectric properties, the gapless character is also a strong drawback since it prevents the separation of the opposite contributions of electrons and holes to the Seebeck coefficient [3]. Thus, opening a sizable bandgap in graphene is required to overcome the disadvantages of graphene and to fully benefit from its excellent conduction properties. Although many nanostructuring techniques can be used to open such a bandgap in graphene, e.g., graphene nanoribbons, graphene bilayer with a perpendicular electric field, graphene nanomesh lattices, channels based on vertical stack of graphene layers , mixed graphene/hexagonal boron nitride structures, nitrogen doped graphene, etc, each of these methods has its own fabrication issues and/or need to be further confirmed by experiments. In this work, we present our theoretical studies focusing on strain engineering, which offers a wide range of opportunities for modulating the electronic properties of graphene nanostructures. We show that with a strain of only a few percent, the strain-induced shift of the Dirac point in k-space may be enough to open a sizable conduction gap (500 meV or more) in graphene heterojunctions made of unstrained/strained junctions [4]. The effect can be exploited to improve the behavior and performance of several types of devices. We show that, with a strain of only 5%, it is possible to switch off transistors efficiently, with the ON/OFF current ratio of several order of magnitude larger than that of pristine graphene transistors which is not exceeding 10 [5]. By combining strain and doping engineering Seebeck coefficient can reach values higher than 1.4 mV/K, which is 17 times higher than in gapless pristine graphene [6]. This makes graphene an excellent candidate for thermoelectric material as well. Finally, we will show that very strong negative differential conductance (NDC) effects with peak-to-valley ratios of a few hundred at room temperature can be achieved by using appropriate strain engineering in graphene diodes made of either single gate-induced strained barrier or a p-n junction [7]. [1] A. C. Ferrari et al., Nanoscale 7, 4598 (2015). [2] Ha et al, Electron Device Lett. IEEE 34, 559 (2013). [3] Zuev et al, Phys. Rev. Lett. 102, 096807 (2009). [4] M. C. Nguyen et al., Semicond. Sci. Technol. 29,115024(2014). [5] V. H. Nguyen et al., Nanotechnology 25, 165201 (2014). [6] M. C. Nguyen et al., Physica E 73, 207(2015). [7] M. C. Nguyen et al., J. Appl. Phys. 118, 234306(2015).

Presenter: Nguyen Mai Chung