Vertical Tunneling in Layered Materials and Its Applications*

Tunneling has to play an essential role in vertical transport in layered materials due to the van der Waals coupling between layers. The van der Waals gap can be viewed as the thinnest insulator, with a physical thickness of about 3-5 angstrom measured from the center of the nearest atomic planes separated by the van der Waals gap (not the centroid of a monolayer). When an electron wavelet moves perpendicular to this gap, is it sufficient to use the transfer-Hamiltonian method to calculate the time it takes thus calculating the magnitude of the resulting current flow? Is it possible to control tunneling with an applied electric field thus possible to generate a signal? Being one of the most sensitive transport mechanisms, it is difficult to reach very high tunneling current density. In resonant tunneling diodes, very high tunneling peak currents are achieved (\textasciitilde MA/cm$^{\mathrm{2}})$; however, the valley current increases concurrently, thus limiting the range of tunable tunneling current to a typical value of \textless 5. Finally, how is tunneling in layered materials different from 3D materials? These are the questions our group has aimed to answer [1-8]. In this talk, I will share our progress and the challenges we face in terms of preparing, characterizing these layered materials as well as pursuing their applications. \begin{enumerate} \item Mingda (Oscar) Li, Huili Grace Xing et al. \textit{Single particle transport in two-dimensional heterojunction interlayer tunneling field effect transistor}. J. Appl. Phys. 115, 074508 (2014). doi:10.1063/1.4866076 \item Shudong Xiao, Mingda Li,~Alan Seabaugh, Debdeep Jena,~Huili Grace Xing. \textit{Vertical heterojunction of MoS2 and WSe2.} IEEE Device Research Conference, University of California, Santa Barbara, June 2014. \item Debdeep Jena,~Mingda Li,~Nan Ma, Wan Sik Hwang, David Esseni, Alan~Seabaugh, and~Huili Grace Xing. \newline \textit{Electron transport in 2D crystal semiconductors and their device applications.} IEEE Silicon Nanoelectronics Workshop, Hawaii, June 2014. \item Rusen Yan, Huili Grace Xing et al.,~\textit{Esaki diodes in van der Waals heterojunctions with broken-gap energy band alignment}.~Nano Letters, 15(9), 5791-8, (2015). DOI: 10.1021/acs.nanolett.5b01792 \item Mingda (Oscar) Li, David Esseni, Gregory Snider, Debdeep Jena and~Huili Grace Xing.~\textit{Two-dimensional heterojunction interlayer tunneling field effect transistors (Thin-TFET)}~IEEE J-EDS, 3(3), 200-207 (2015). DOI:10.1109/JEDS.2015.2390643 \item ~Mingda (Oscar) Li, Rusen Yan, Debdeep Jena and Huili Grace Xing. \textit{Two-dimensional Heterojunction Interlayer Tunnel Field Effect Transistor (Thin-TFET): From Theory to Applications.} IEDM, pp.19.2/1-4, (2016) \item Mingda (Oscar) Li, Ozan Irsoy, Claire Cardie, and Huili Grace Xing. \textit{Physics-inspired neural networks (Pi-NN) for efficient device compact modeling.} IEEE J. of Exploratory Solid-State Computational Devices and Circuits (2016). \item Jimy Encomendero, Faiza Afroz Faria, S. M. Islam, Vladimir Protasenko, Sergei Rouvimov, Berardi Sensale-Rodriguez, Patrick Fay, Debdeep Jena, and Huli Grace Xing. \textit{New tunneling features in polar III-nitride resonant tunneling diodes.} Physics Review X (PRX), 7,041017 (2017).~ DOI: 10.1103/PhysRevX.7.041017 \end{enumerate}