Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session H16: 2D Devices: Electronics and OptoelectronicsFocus
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Sponsoring Units: DMP Chair: Jonathan Bird, University at Buffalo Room: 315 |
Tuesday, March 15, 2016 2:30PM - 3:06PM |
H16.00001: Nano-scale electronic and optoelectronic devices based on 2D crystals Invited Speaker: Wenjuan Zhu In the last few years, the research community has been rapidly growing interests in two-dimensional (2D) crystals and their applications. The properties of these 2D crystals are diverse --- ranging from semi-metal such as graphene, semiconductors such as MoS$_{\mathrm{2}}$, to insulator such as boron nitride. These 2D crystals have many unique properties as compared to their bulk counterparts due to their reduced dimensionality and symmetry. A key difference is the band structures, which lead to distinct electronic and photonic properties. The 2D nature of the material also plays an important role in defining their exceptional properties of mechanical strength, surface sensitivity, thermal conductivity, tunable band-gap and their interaction with light. These unique properties of 2D crystals open up a broad territory of applications in computing, communication, energy, and medicine. In this talk, I will present our work on understanding the electrical properties of graphene and MoS$_{\mathrm{2}}$, in particular current transport and band-gap engineering in graphene, interface between gate dielectrics and graphene, and gap states in MoS$_{\mathrm{2}}$. I will also present our work on the nano-scale electronic devices (RF and logic devices) and photonic devices (plasmonic devices and photo-detectors) based on these 2D crystals. [Preview Abstract] |
Tuesday, March 15, 2016 3:06PM - 3:18PM |
H16.00002: Direct Visualization of Edge States and Electrical Inhomogeneity in MoS$_{2}$ Field Effect Transistors Di Wu, Lan Luan, Zhaodong Chu, Xiaoyu Wu, Keji Lai Ultrathin transition metal dichalcogenides (TMDs) with layer-dependent bandgaps, relatively high carrier mobilities, and valley pseudospins are promising material platforms for novel electronics. It is of great importance to microscopically probe the TMD-based electronic devices for understanding and improving their performances in relation to metal contacts, interfaces, and defects. Here, we report the electrical imaging of the channel conductance of few-layer MoS$_{2}$ field-effect transistors by microwave impedance microscopy (MIM). A systematic evolution of the local conductance of exfoliated MoS2 back-gated devices was captured during the insulator-to-metal transition induced by electrostatic gating. Interestingly, when the transistors were gradually turned on, the carriers were first accumulated at the edges of MoS2 flakes, as indicated by the higher local conductivity in MIM images. At the same time, we have also observed strong local conductance fluctuation, which are presumably due to the charged impurities in the flakes or defects at the interfaces. The MIM images can thus provide us the microscopic understanding of how the device performance is influenced by the local defects and edge states. [Preview Abstract] |
Tuesday, March 15, 2016 3:18PM - 3:30PM |
H16.00003: Tunnelling in van der Waals heterostructures Artem Mishchenko, Kostya Novoselov, Andre Geim, Laurence Eaves, Vladimir Falko When graphene and other conductive two-dimensional (2D) materials are separated by an atomically thin insulating 2D crystal, quantum mechanical tunnelling leads to appreciable current between two 2D conductors due to the overlap of their wavefunctions. These tunnel devices demonstrate interesting physics and potential for applications: such effects as resonant tunnelling, negative differential conductance, light emission and detection have already been demonstrated. In this presentation we will outline the current status and perspectives of tunnelling transistors based on 2D materials assembled into van der Waals heterostructures. Particularly, we will present results on mono- and bilayer graphene tunnelling, tunnelling in 2D crystal-based quantum wells, and tunnelling in superconducting 2D materials. Such effects as momentum and chirality conservation, phonon- and impurity-assisted tunnelling will also be discussed. Finally, we will ponder the implications of discovered effects for practical applications. [Preview Abstract] |
Tuesday, March 15, 2016 3:30PM - 3:42PM |
H16.00004: Fabrication and characterization of graphene PN junctions Dennis Wang, Xiaodong Zhou, Ali Dadgar, Pratik Agnihotri, Ji Ung Lee, Mark Reuter, Frances Ross, Abhay Pasupathy Theoretical predictions of relativistic Klein tunneling and Veselago lensing in graphene have inspired efforts to fabricate graphene p-n junctions where such phenomena could be realized and studied via electronic transport or scanning tunneling microscopy (STM). Here we will discuss the interplay between device geometry and our measurements in a 4-probe STM, which allows for simultaneous back gating, biasing, and scanning of a micromechanically exfoliated graphene sample. A sharp p-n junction is essential to the manifestation of these aforementioned effects, and we examine the benefits and drawbacks of several routes toward this goal from a fabrication standpoint. These methods include lithographically pre-patterned substrates and the stacking of vertical heterostructures. Finally, we will describe our subsequent characterization results for each, including information about topography and spatial mapping of the density of states. [Preview Abstract] |
Tuesday, March 15, 2016 3:42PM - 3:54PM |
H16.00005: Graphene -- ferroelectric and MoS2 -- ferroelectric heterostructures for memory applications. Alexey Lipatov, Pankaj Sharma, Alexei Gruverman, Alexander Sinitskii In recent years there has been an unprecedented interest in two-dimensional (2D) materials with unique physical and chemical properties that cannot be found in their three-dimensional (3D) counterparts. One of the important advantages of 2D materials is that they can be easily integrated with other 2D materials and functional films, resulting in multilayered structures with new properties. We fabricated and tested electronic and memory properties of field-effect transistors (FETs) based on a single-layer graphene combined with lead zirconium titanate (PZT) substrate. Previously studied graphene-PZT devices exhibited an unusual electronic behavior such as clockwise hysteresis of electronic transport, in contradiction with counterclockwise polarization dependence of PZT. We investigated how the interplay of polarization and interfacial phenomena affects the electronic behavior and memory characteristics of graphene-PZT FETs, explain the origin of unusual clockwise hysteresis and experimentally demonstrate a reversed polarization-dependent hysteresis of electronic transport. In addition we fabricated and tested properties of MoS2-PZT FETs which exhibit a large hysteresis of electronic transport with high ON/OFF ratios. We demonstrate that MoS2-PZT memories have a number of advantages over commercial FeRAMs, such as nondestructive data readout, low operation voltage, wide memory window and the possibility to write and erase them both electrically and optically. [Preview Abstract] |
Tuesday, March 15, 2016 3:54PM - 4:06PM |
H16.00006: Programmable Schottky Junctions Based on Ferroelectric Gated MoS$_{\mathrm{2}}$ Transistors. Zhiyong Xiao, Jingfeng Song, Stephen Drcharme, Xia Hong We report a programmable Schottky junction based on MoS$_{\mathrm{2}}$ field effect transistors with a SiO$_{\mathrm{2}}$ back gate and a ferroelectric copolymer poly(vinylidene-fluoride-trifluorethylene) (PVDF) top gate. We fabricated mechanically exfoliated single layer MoS$_{\mathrm{2}}$ flakes into two point devices via e-beam lithography, and deposited on the top of the devices \textasciitilde 20 nm PVDF thin films. The polarization of the PVDF layer is controlled locally by conducting atomic force microscopy. The devices exhibit linear $I_{\mathrm{D}}$-$V_{\mathrm{D\thinspace }}$characteristics when the ferroelectric gate is uniformly polarized in one direction. We then polarized the gate into two domains with opposite polarization directions, and observed that the $I_{\mathrm{D}}$-$V_{\mathrm{D\thinspace }}$characteristics of the MoS$_{\mathrm{2}}$ channel can be modulated between linear and rectified behaviors depending on the back gate voltage. The nonlinear $I_{\mathrm{D}}$-$V_{\mathrm{D\thinspace }}$relation emerges when half of the channel is in the semiconductor phase while the other half is in the metallic phase, and it can be well described by the thermionic emission model with a Schottky barrier of \textasciitilde 0.5 eV. The Schottky junction can be erased by re-write the entire channel in the uniform polarization state. Our study facilitates the development of programmable, multifunctional nanoelectronics based on layered 2D TMDs.. [Preview Abstract] |
Tuesday, March 15, 2016 4:06PM - 4:18PM |
H16.00007: Control of Rewriteable Doping Patterns in Graphene/Boron Nitride Heterostructures Salman Kahn, Jairo Velasco Jr., Dillon Wong, Juwon Lee, Hsin Zon Tsai, Long Ju, Lili Jiang, Zhiwen Shi, Paul Ashby, Takashi Taniguchi, Kenji Watanabe, Alex Zettl, Feng Wang, Michael Crommie Spatial control of charge doping in 2D materials is a promising technique for designing future electronic devices and understanding novel physics. Electrostatic gating and chemical doping are common methods to achieve control of charge doping in 2D materials. However, these approaches suffer from complicated fabrication processes that introduce impurities, change material properties irreversibly, and lack flexibility. Here, we introduce a new method for patterning rewriteable doping profiles with local interface charge transfer from defects in a tunable BN substrate into an adjacent layer of graphene. We characterize these spatial doping patterns through local probe and transport techniques. This technique enables many novel device designs for 2D materials, including atomically thin p-n junctions and rewriteable memory devices. [Preview Abstract] |
Tuesday, March 15, 2016 4:18PM - 4:30PM |
H16.00008: Spatially inhomogeneous barrier height in graphene/MoS2 Schottky junctions Dushyant Tomer, Shivani Rajput, Lian Li Graphene interfaced with a semiconductor forms a Schottky junction with rectifying properties. In this study, graphene Schottky junctions are fabricated by transferring CVD monolayer graphene on mechanically exfoliated MoS$_{2}$ multilayers. The forward bias current--voltage characteristics are measured in the temperature range of 210--300 K. An increase in the zero bias barrier height and decrease in the ideality factor are observed with increasing temperature. Such behavior is attributed to Schottky barrier inhomogeneities possibly due to graphene ripples and ridges at the junction interface as suggested by atomic force microscopy. Assuming a Gaussian distribution of the barrier height, mean barrier of 0.97\textpm 0.10 eV is found for the graphene MoS$_{2}$ junction. Our findings provide significant insight on the barrier height inhomogeneities in graphene/two dimensional semiconductor Schottky junctions. [Preview Abstract] |
Tuesday, March 15, 2016 4:30PM - 4:42PM |
H16.00009: Phase change memory devices formed by using 2 dimensional layered Graphene-In2Se3 van der Waals heterostructure. Min Sup Choi, Chenxi Yang, Chang Ho Ra, Won Jong Yoo Indium selenide (In2Se3) is one of the unique materials which have both a layered structure and phase change property. One of the advantages of using 2 dimensional (2D) materials is their potential to form van der Waals heterostructures which enable unique physical properties and novel quantum device functions, which cannot be achieved in 2D material alone. In this study, we fabricated vertically stacked graphene-In2Se3 heterostructured memory devices. The fabricated devices showed a rapid increase of current conduction, which is attributed to the phase transition of In2Se3. The TEM images demonstrated that In2Se3 transformed from polycrystalline to layered structure thanks to the effective thermal confinement effect between graphene and In2Se3, attributed to the low thermal conductivity of layered materials in vertical direction. In addition, the current conduction could be controlled effectively by applying different pulse voltages, showing stable retention and endurance characteristics. It is thought that the differently bonded states contribute to this control process. This study demonstrates the possibility of Graphene-In2Se3 van der Waals heterostructure as 2D based future memory electronics. [Preview Abstract] |
Tuesday, March 15, 2016 4:42PM - 4:54PM |
H16.00010: Optoelectronic devices based on MoTe$_{\mathrm{2}}$ p-n junction. Ya-Qing Bie, Mikkel Heuck, Marco Furchi, Gabriele Grosso, Jiabao Zheng, Yuan Cao, Efren Navarro-Moratalla, Dirk Englund, Pablo Jarillo-Herrero 2D transition metal dichalcogenides (2D-TMD), such as MoS$_{\mathrm{2}}$, have been verified with many remarkable physical properties, which include an indirect to direct band transition as a function of thickness and a valley dependent spin polarization. One of the 2D-TMD family members, 2H-MoTe$_{\mathrm{2}}$ has been shown to be a direct bandgap semiconductor as a monolayer and bilayer with a near infrared (NIR) bandgap of about 1.1eV. However, optoelectronic devices based on MoTe2 were so far not experimentally demonstrated. Here, we will present a high on-off ratio MoTe$_{\mathrm{2}}$ p-n junction enabled by a hexagonal boron nitride encapsulation technique. Our study of the MoTe$_{\mathrm{2}}$ p-n junction devices sheds light on designing efficient NIR optoelectronic devices such as photodetectors and energy harvesting cells and light emitters. [Preview Abstract] |
Tuesday, March 15, 2016 4:54PM - 5:06PM |
H16.00011: \textbf{Polarization and resistive switching behavior of ferroelectric tunnel junctions with }\textbf{transition metal }\textbf{dichalcogenides} Tao Li, Alexey Lipatov, Pankaj Sharma, Hyungwoo Lee, Chang-Beom Eom, Alexander Sinitskii, Alexei Gruverman Transition metal dichalcogenides (TMDs) are emerging 2-dimensional (2D) materials of the MX$_{\mathrm{2}}$ type, where M is a transition metal atom (Mo, W, Ti, Sn, Zr, etc.) and X is a chalcogen atom (S, Se, or Te.). Comparing to graphene, TMDs have a sizable band gap and can be metal, half-metal, semiconductor or superconductor. Their band structures can be tuned by external bias voltage, mechanical force, or light illumination. Their rich physical properties make TMDs potential candidates for a variety of applications in nanoelectronics and optoelectronics. Ferroelectric tunnel junctions (FTJs) are actively studied as a next-generation of non-volatile memory elements. An FTJ comprises a ferroelectric tunnel barrier sandwiched between two electrodes. In this work, we investigate the resistive switching behavior of MoS$_{\mathrm{2}}$/BaTiO$_{\mathrm{3}}$-based FTJs. The ON/OFF ratio can be modulated via electric or mechanical control of the switched polarization fraction opening a possibility of tunable electroresistance effect. Effect of optical illumination on the polarization reversal dynamics has been observed and analyzed based on the polarization-induced modulation of the MoS$_{\mathrm{2}}$ layered electronic properties. [Preview Abstract] |
Tuesday, March 15, 2016 5:06PM - 5:18PM |
H16.00012: Atomic-scaled characterization of graphene PN junctions Xiaodong Zhou, Dennis Wang, Ali Dadgar, Pratik Agnihotri, Ji Ung Lee, Mark C. Reuter, Frances M. Ross, Abhay N. Pasupathy Graphene p-n junctions are essential devices for studying relativistic Klein tunneling and the Veselago lensing effect in graphene. We have successfully fabricated graphene p-n junctions using both lithographically pre-patterned substrates and the stacking of vertical heterostructures. We then use our 4-probe STM system to characterize the junctions. The ability to carry out scanning electron microscopy (SEM) in our STM instrument is essential for us to locate and measure the junction interface. We obtain both the topography and \textit{dI/dV} spectra at the junction area, from which we track the shift of the graphene chemical potential with position across the junction interface. This allows us to directly measure the spatial width and roughness of the junction and its potential barrier height. We will compare the junction properties of devices fabricated by the aforementioned two methods and discuss their effects on the performance as a Veselago lens. [Preview Abstract] |
Tuesday, March 15, 2016 5:18PM - 5:30PM |
H16.00013: ABSTRACT WITHDRAWN |
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