Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session V1: 2D Electronic Devices and Device Physics |
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Sponsoring Units: DMP DCMP Chair: Kin Fai Mak, Penn State University Room: 260 |
Thursday, March 16, 2017 2:30PM - 2:42PM |
V1.00001: Extraction of interlayer coupling and hopping potentials with misaligned hBN tunnel barriers in graphene/hBN/graphene tunnel FETs Amithraj Valsaraj, Leonard F. Register, Sanjay K. Banerjee Reduction in interlayer tunneling due to weakened coupling across the rotationally misaligned interface between the channel layers and the tunnel barrier has been studied using atomistic density functional theory (DFT) simulations. The effects of rotational misalignment of the tunnel barrier layer between aligned channel layers was simulated with a prototypical graphene/hBN/graphene system. DFT simulation results suggest that the interlayer tunneling current for such heterostructures will be affected strongly by the rotational alignment of the hBN interface with respect to the graphene layers. We find that rotational misalignment between the channel layers and the tunnel barrier in this van der Waal's heterostructure can significantly reduce coupling between the channels by reducing, specifically, coupling across the interface between the channels and the tunnel barrier. Further, the hopping potentials for rotationally misaligned graphene/hBN/graphene were calculated using maximally localized Wannier functions technique, towards a better understanding of the source of reduced coupling. [Preview Abstract] |
Thursday, March 16, 2017 2:42PM - 2:54PM |
V1.00002: Electrical and Optical Characteristics of Undoped and Se-Doped Bi$_{\mathrm{2}}$S$_{\mathrm{3}}$ Transistors Colin Kilcoyne, Ali Alsaqqa, Ajara A. Rahman, Luisa Whittaker-Brooks, G. Sambandamurthy Semiconducting chalcogenides have been drawing increased attention due to their interesting physical properties, especially in low dimensional structures. Bi$_{\mathrm{2}}$S$_{\mathrm{3}}$ has demonstrated a high optical absorption coefficient, a large bulk mobility, small bandgap, high Seebeck coefficient, and low thermal conductivity. These properties make it a good candidate for optical, electric and thermoelectric applications. However, control over the electrical properties for enhanced thermoelectric performance and optical applications is desired. We present electrical transport and optical properties from individual nanowire and few-layer transistors of single crystalline undoped and Se-doped Bi$_{\mathrm{2}}$S$_{\mathrm{3-x}}$Se$_{\mathrm{x}}$. All devices exhibit n-type semiconducting behavior and the ON/OFF ratio, mobility, and conductivity noise behavior are studied as functions of dopant concentration, temperature, and charge carrier density in different conduction regimes. The roles of dopant driven scattering mechanisms and mobility/carrier density fluctuations will be discussed. The potential for this series of materials as optical and electrical switches will be presented. [Preview Abstract] |
Thursday, March 16, 2017 2:54PM - 3:06PM |
V1.00003: Screening limited switching performance of multilayer 2D semiconductor FETs: the case for SnS Sukrit Sucharitakul, Rajesh Kumar, Raman Sankar, Fang-Cheng Chou, Yit-Tsong Chen, Chuhan Wang, Cai He, Rui He, Xuan Gao Multilayer tin mono-sulfide (SnS) field-effect transistor (FET) devices with thickness between 50 to 100 nm with gate tunable p-type carriers were fabricated and studied. The fabricated devices demonstrated anisotropic inplane conductance and room temperature field effect mobility ranging from 5 to 10 cm$^{\mathrm{2}}$/Vs. However, weak gate tuning was shown to underestimate the field effect mobility. The finite screening length effect was demonstrated to be the cause of appreciable OFF state conductance, ON-OFF ratio of 10 at room temperature and the weak gate tuning. Etching and n-type surface doping by Cs$_{\mathrm{2}}$CO$_{\mathrm{3}}$ to reduce non-gatable holes near the sample's top surface were perform and the devices showed an order of magnitude improvement in the ON-OFF ratio and hole Hall mobility \textasciitilde 100 cm$^{\mathrm{2}}$/Vs at room temperature is observed. This demonstrates that in order to obtain strong gate effect and switching on 2D semiconductor, the samples thickness must lie within the regime of Debye screening length. Work's online publication:~DOI: 10.1039/C6NR07098A.~\underline {\textbf{arXiv:1608.06501}} [Preview Abstract] |
Thursday, March 16, 2017 3:06PM - 3:18PM |
V1.00004: Valley FETs in graphene Yu-Shu Wu, Feng-Wu Chen, Mu-Kuen Lee, Maio-Ling Lin, Ning-Yuan Lue, Yen-Chun Chen Graphene electrons carry a unique binary degree of freedom called valley pseudospin, in association with the two-fold valley degeneracy at the Dirac points (K and K') of Brillouin zone. Such pseudospin responds to external electromagnetic fields in ways similar to those an ordinary electron spin does, and hence qualifies for an information carrier [1]. Implementation of the corresponding electronics -- valleytronics can be carried out in a unified fashion, namely, by utilizing the valley-orbit interaction (VOI) existing between an in-plane electric field and a valley pseudospin. Based on the VOI mechanism, a family of valleytronic structures have been proposed, such as valley qubits, valley filters, and valley FETs [2]. This presentation discusses the valley FET as an example to demonstrate such a methodology. Specifically, it will describe the underlying principle as well as our recent numerical simulation of electron transport through this structure based on the algorithm of recursive Green's function method. [1] Rycerz et al., Nat. Phys. 3 (2007),172; Xiao et al., Phys. Rev. Lett. 99, (2007), 236809. [2] Wu et al., Phys. Rev. B 84, (2011), 195463; ibid B 86 (2012), 165411; ibid B 88 (2013), 125422; ibid B 94 (2016), 075407. [Preview Abstract] |
Thursday, March 16, 2017 3:18PM - 3:30PM |
V1.00005: Shot noise detection in hBN-based tunnel junctions Panpan Zhou, Will Hardy, Kenji Watanabe, Takashi Taniguchi, Douglas Natelson Shot noise, which originates from the discreteness of charge carriers, can provide more information about charge transport than the average current. The tunneling current noise in a normal single electron system is given by $S=2eI$ when $eV\gg 2k_B T$. While in strongly correlated systems, where the electron Coulomb repulsion is not negligible, the shot noise might deviate from this classical result. Here we demonstrate a technique that can be adapted to study the shot noise in strongly correlated systems. High quality Au/hBN/Au tunneling devices are fabricated using transferred atomically thin hexagonal boron nitride as the tunneling barrier. All tunneling junctions show specific resistance on the order of several $k\Omega / {\mu m}^2$, which agrees with previous reported hBN-based tunnel junction properties. The ohmic-like $I-V$ curves at small bias range indicate the sparsity of defects. Tunneling current shot noise is measured in these devices and the excess shot noise shows great consistency with theoretical expectation. These results show that atomically thin hBN is an excellent tunneling barrier, especially for the study of shot noise properties, which might be a useful tool to study the charge transport properties in complicated systems. [Preview Abstract] |
Thursday, March 16, 2017 3:30PM - 3:42PM |
V1.00006: Strong Coulomb scattering effects in monolayer WS$_{\mathrm{2}}$ transistor analyzed by low-frequency noise measurement Yoojoo Yun, Min-Kyu Joo, Seokjoon Yun, Young Hee Lee, Dongseok Suh A monolayer tungsten disulfide (WS$_{\mathrm{2}})$ has recently gained great interests as a new semiconducting material for electronic device due to the controllability of bandgap depending on its thickness, high thermal stability and on/off ratio. In real application, however, those intrinsic properties are easily affected by the extrinsic environmental factors such as substrate doping and surface roughness. Especially, the largely distributed interfacial Coulomb impurities give rise to the severe carrier fluctuation, limiting a signal-to-noise ratio. Here, we report the strong Coulomb scattering effect on low-frequency (LF) noise in monolayer WS$_{\mathrm{2}}$ FETs in respect of temperature [1]. For the better device performance, a nitrogen annealing was carried out. The experimental results are explained well with the carrier number fluctuation and correlated mobility fluctuation model (CNF-CMF), and it is discussed that the electronic transport of WS$_{\mathrm{2}}$ transistor can be strongly dominated by the enhanced Coulomb scattering source located in WS$_{\mathrm{2}}$ channel with carrier trapping/de-trapping processes into the oxide traps. [1] Y. Yun, M. Joo, et al., Appl. Phys. Lett. 109, 153102 (2016) [Preview Abstract] |
Thursday, March 16, 2017 3:42PM - 3:54PM |
V1.00007: Abstract Withdrawn
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Thursday, March 16, 2017 3:54PM - 4:06PM |
V1.00008: Interface states analysis in atomically thin MoS$_{\mathrm{2}}$ FET Nan Fang, Kosuke Nagashio Two-dimensional (2D) materials such as MoS$_{\mathrm{2}}$ have recently attracted much attention for use in next-generation field-effect transistors (FETs). The interface between the channel and gate insulator should be seriously considered especially for atomically thin channel devices. Defects in MoS$_{\mathrm{2}}$ as well as dangling bonds from gate oxide could contribute to the interface states. At present, interface states density ($D_{\mathrm{it}})$ of MoS$_{\mathrm{2}}$ FET extracted by various kinds of electrical measurements is largely scattered and very large. This large $D_{\mathrm{it\thinspace }}$should affect carrier transport seriously. Here, in order to gain insight to reduce $D_{\mathrm{it}}$, we study the correlation between interface states and carriers in terms of random telegraphic signals (RTSs) analysis, which complements noise study of MoS$_{\mathrm{2}}$. RTSs measurements for multi-probe devices confirm that the defects at the channel/insulator interface cause RTSs. Moreover, conductance method is also applied for dual-gated MoS$_{\mathrm{2}}$ FET to extract $D_{\mathrm{it}}$ and its time constant. In this talk, we focus on the RTSs analysis and conductance measurements for thin MoS$_{\mathrm{2}}$ FET to study interface states. [Preview Abstract] |
Thursday, March 16, 2017 4:06PM - 4:18PM |
V1.00009: Depin MoS$_{\mathrm{2}}$ Fermi Level via One-Dimensional Contact Zheng Yang, Chang Ho Ra, Won Jong Yoo In this work, we depin MoS$_{\mathrm{2}}$/metal contact using MoS$_{\mathrm{2}}$/metal one-dimensional (1D) contact via controllable plasma etching. An intrinsic MoS$_{\mathrm{2}}$/Pd 1D contact FET fabricated in this study shows ambipolar behavior. While an intrinsic MoS$_{\mathrm{2}}$/Mo 1D contact FET fabricated shows n-type behavior with a two-probe field-effect electron mobility of 96 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$. With four-probe transport measurement, we obtain a maximum field-effect hole mobility, 9 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$ at 300 K. At 70 k, it increases to around 393 cm$^{\mathrm{2}}$V$^{\mathrm{-1}}$s$^{\mathrm{-1}}$. With the use of this MoS$_{\mathrm{2}}$/metal 1D contact, we successfully demonstrate an inverter formed on intrinsic MoS$_{\mathrm{2}}$, whose gain is \textasciitilde 14.7 at V$_{\mathrm{SD}}=$5 V. Our work opens a door to simply realizing complementary integrated circuitry, based on high performance intrinsic MoS$_{\mathrm{2}}$. [Preview Abstract] |
Thursday, March 16, 2017 4:18PM - 4:30PM |
V1.00010: Large scale commercial fabrication of high quality graphene-based assays for biomolecule detection Mitchell Lerner, Yingning Gao, Brett Goldsmith, Francie Barron Large numbers of high quality graphene transistors with mobility approximately 5000 $cm^2/V*s$ were fabricated by chemical vapor deposition and packaged into ceramic carriers with an open cavity design. The ceramic carrier is compatible with standard electronics assembly, enabling the readout of graphene properties on the benchtop without large, expensive probing systems. After chemical functionalization, these sensors demonstrate sensitivity in the pM range and selectivity to many classes of biomolecules as a three terminal liquid-gated field effect transistor. High precision measurements of protein kinetics captured using this technology, commercially known as AGILE R100, are comparable and can exceed the capabilities of state-of-the-art biomolecule characterization tools. Recently published in Sensors and Actuators B [Preview Abstract] |
Thursday, March 16, 2017 4:30PM - 4:42PM |
V1.00011: Electron optics lab-on-chip: Absorptive pinhole collimators for ballistic electrons in graphene Arthur W. Barnard, Alex Hughes, Aaron L. Sharpe, Kenji Watanabe, Takashi Taniguchi, David Goldhaber-Gordon In the absence of scattering, electrons in graphene propagate as unperturbed waves, analogous to photons propagating in free space. However, these electrons possess distinctive interparticle interactions and unique refractive properties. These traits, in conjunction with the emerging capability of fabricating ultraclean graphene devices, have inspired widespread interest in on-chip electron optical systems built from graphene. While such systems have great promise, graphene's inherent chiral transport presents a unique challenge: chiral electrons cannot be readily confined by electrostatic gates. We overcome this fundamental challenge and present an attractively simple means of forming a collimated electron beam, an important building block for electron optical devices. Our collimators are formed by etched collinear slits combined with absorptive ohmic sidewalls between the slits. Here, we experimentally demonstrate collimated beams with full-width half maxima of 18 degrees or narrower. We use our collimators to form ballistic magnetometers as well as to directly observe Klein tunneling. [Preview Abstract] |
Thursday, March 16, 2017 4:42PM - 4:54PM |
V1.00012: A 2D Material based Gate Tunable Memristive Device for Emulating Modulatory Input-dependent Hetero-synaptic Plasticity. Xiaodong Yan, He Tian, Yujun Xie, Andrew Kostelec, Huan Zhao, Judy J. Cha, Jesse Tice, Han Wang Modulatory input-dependent plasticity is a well-known type of hetero-synaptic response where the release of neuromodulators can alter the efficacy of neurotransmission in a nearby chemical synapse. Solid-state devices that can mimic such phenomenon are desirable for enhancing the functionality and reconfigurability of neuromorphic electronics. In this work, we demonstrated a tunable artificial synaptic device concept based on the properties of graphene and tin oxide that can mimic the modulatory input-dependent plasticity. By using graphene as the contact electrode, a third electrode terminal can be used to modulate the conductive filament formation in the vertical tin oxide based resistive memory device. The resulting synaptic characteristics of this device, in terms of the profile of synaptic weight change and the spike-timing-dependent-plasticity, is tunable with the bias at the modulating terminal. Furthermore, the synaptic response can be reconfigured between excitatory and inhibitory modes by this modulating bias. The operation mechanism of the device is studied with combined experimental and theoretical analysis. The device is attractive for application in neuromorphic electronics. [Preview Abstract] |
Thursday, March 16, 2017 4:54PM - 5:06PM |
V1.00013: Electrical Transport of an Electron-Hole Double Layer with a Middle Barrier Wu Xing-Jun, Liu Ruiyuan, Lou Wenkai, Chang Kai, Sullivan Gerard, Du Rui-Rui It was proposed that in a spatially separated electron-hole system like InAs-GaSb-based quantum wells, spontaneous excitonic ground states could form under proper conditions. Motivated by this prospect and with the advent of high quality materials grown by MBE, we explore low temperature electrical transport properties in InAS/GaInSb bilayers with a AlSb middle barrier. The devices were made with flip-chip techniques to facilitate dual-gate control of carrier densities. We will report preliminary results, and a brief discussion will be presented. [Preview Abstract] |
Thursday, March 16, 2017 5:06PM - 5:18PM |
V1.00014: Correlating Crystal Quality with Electronic Properties in Transition Metal Dichalcogenide Semiconductors Drew Edelberg, Irene Zhang, Daniel Rhodes, Benjamin Foutty, Fernando Stavale, Luis Balicas, James Hone, Abhay Pasupathy Monolayer transition metal dichalcogenides (TMD) have given rise to a new era of two-dimensional layered, semiconducting devices for electronics and optoelectronics applications. One of the limiting features in TMD materials is the presence of traps and scattering centers that lead to a degradation of performance. These defects can lie either in the monolayer TMD itself, or can exist in the substrate that the monolayer is placed on. A better understanding of the disorder affecting these materials can be achieved by separating intrinsic sources of disorder (ie, defects within the crystal) from extrinsic ones. To do this, we present a study of cleaved bulk crystals of the TMD semiconductor MoSe2 using atomic-resolution scanning tunneling microscopy (STM) and spectroscopy (STS). We study bulk crystals of MoSe2 grown using two established techniques, chemical vapor transport (CVT) and flux-based growth. STM measurements reveal that crystals grown by selenium flux have a sharply lower defect concentration when compared to images taken on CVT grown crystals. Analysis of local electronic structure using STS reveals both acceptor and donor defects that cause local bandgap shifts. Finally, we correlate our STM data with optical measurements of excitonic lifetimes to show that intrinsic defects have a direct relationship to the quality of monolayer TMD devices. [Preview Abstract] |
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