Bulletin of the American Physical Society
APS March Meeting 2014
Volume 59, Number 1
Monday–Friday, March 3–7, 2014; Denver, Colorado
Session Y51: Focus Session: Beyond Graphene Devices: Function, Fabrication, and Characterization VIII |
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Sponsoring Units: DMP Chair: Peide Ye, Purdue University Room: Mile High Ballroom 1E |
Friday, March 7, 2014 8:00AM - 8:12AM |
Y51.00001: Phosphorene: A New High-Mobility 2D Semiconductor Han Liu, Adam Neal, Zhen Zhu, David Tomanek, Peide Ye The rise of 2D crystals has opened various possibilities for future electrical and optical applications. MoS$_{\mathrm{2}}$ n-type transistors are showing great potential in ultra-scaled and low-power electronics. Here, we introduce phosphorene, a name we coined for 2D few-layer black phosphorus, a new 2D material with layered structure. We perform \textit{ab initio} band structure calculations and show that the fundamental band gap depends sensitively on the number of layers. We observe transport behavior, which shows a mobility variation in the 2D plane. High on-current of 194 mA/mm, high hole mobility up to 286 cm$^{\mathrm{2}}$/V$\cdot $s and on/off ratio up to 10$^{\mathrm{4}}$ was achieved with phosphorene transistors at room temperature. Schottky barrier height at the metal/phosphorene interface was also measured as a function of temperature. We demonstrate a CMOS inverter with combination to MoS$_{\mathrm{2}}$ NMOS transistors, which shows great potential for semiconducting 2D crystals in future electronic, optoelectronic and flexible electronic devices. [Preview Abstract] |
Friday, March 7, 2014 8:12AM - 8:24AM |
Y51.00002: Photostability of thin exfoliated black phosphorus Alexandre Favron, S\'ebastien Francoeur, Richard Leonelli, Richard Martel In its bulk form, black phosphorus has a direct gap of about 0.3 eV. Because of its lamellar structure, similar to that of graphite, black phosphorus can be exfoliated down to a single monolayer. The interesting properties is the possible tuning of the energy gap in the Near-IR using control of the layer thickness, which is of great interesting to develop sensors and other Near-IR optoelectronic devices. Preliminary studies on thin exfoliated layers revealed a fast photo-induced oxidation of black phosphorus, in room condition with an excitation higher than 1.8 eV. Using Raman spectroscopy as a probe of the quality and integrity of exfoliated layers, we present in this talk the results of a dynamical study of the photo-oxidation process at room temperature in a controlled atmosphere with the presence of the oxygen-water redox couple. A photo-induced charge transfer from black phosphorus to the redox couple is found to be responsible of the fast deterioration of the structure. Finally, we present Raman and Photoluminescence results on un-oxidized thin-layers measured at low temperature using different passivation schemes. [Preview Abstract] |
Friday, March 7, 2014 8:24AM - 8:36AM |
Y51.00003: Electronic transport and device properties of monolayer CVD MoS$_{2}$ Wenjuan Zhu, Tony Low, Yi-Hsien Lee, Han Wang, Damon B. Farmer, Jing Kong, Fengnian Xia, Phaedon Avouris The electronic transport and device properties of monolayer molybdenum disulphide (MoS$_{2})$ grown by chemical vapor deposition (CVD) are studied in this work. We show that these devices have the potential to suppress short channel effects, be aggressively down-scaled and have high critical breakdown electric field. These properties make them a compelling alternative to organic and other thin film materials. However, our study reveals that the electronic properties of these devices are at present, severely limited by the presence of a significant amount of band tail trapping states. Through capacitance and ac conductance measurements, we systematically quantify the density-of-states and response time of these states. Due to the large amount of trapped charges, the measured effective mobility also leads to a large underestimation of the true band mobility and the potential of the material. These exponentially distributed states further limit the device's subthreshold slope to 200meV/dec, regardless of the temperature. Continual engineering efforts on improving the sample quality are needed for its potential applications in flexible electronics, high resolution displays, photo-detection and energy harvesting. [Preview Abstract] |
Friday, March 7, 2014 8:36AM - 8:48AM |
Y51.00004: Substrate Effect on Thin Layer MoSe$_{2}$ Field-Effect Transistors with Photo-Response Matthew Z. Bellus, Hui-Chun Chien, David L. Sicilian, Benjamin I. Weintrub, Jatinder Kumar, A. Davis St. Aubin, T.B. Hoffman, Y. Zhang, J.H. Edgar, Hsin-Ying Chiu The discovery of graphene has opened the gates for the study of layered semiconducting materials such as the transition metal dichalcogenides (TMDs), i.e. MoS$_{2}$, MoSe$_{2}$, WS$_{2}$, WSe$_{2}$. In addition, recent works have shown that hexagonal boron nitride (hBN) can act as an ideal substrate with electrical performance enhancement for graphene and possibly for other materials as well. In this study, we examine this substrate effect for MoSe$_{2}$ by comparing various material properties on both SiO$_{2}$ and hBN. Field-effect transistors (FETs) were fabricated on both substrates using mechanically exfoliated MoSe$_{2}$. Our FETs show n-type doping and strong gate modulation yielding I$_{on}$/I$_{off}$ ratios larger than 10$^{6}$ for both substrates. Using a 4-probe measurement we found a relatively high mobility on SiO$_{2}$ that was larger than previous reports, with a slight variation between substrates. Under illumination, devices on both substrates showed ``photo-doping'' effects that in some cases were very large and persistent, thought to be the persistent photoconductivity (PPC) effect. These initial results have shown promising characteristics in MoSe$_{2}$ for applications in electronics and optoelectronics as well as shown the effects that a substrate can play in device performance and material properties. [Preview Abstract] |
Friday, March 7, 2014 8:48AM - 9:00AM |
Y51.00005: Electron/Hole-phonon scattering and intrinsic carrier mobility in 2D transition metal dichalcogenidesĀ (TMDs) Zhenghe Jin, Xiaodong Li, Byoung-Don Kong, Jeffrey Mullen, Ki Wook Kim We have investigated electron/hole-phonon scattering mechanism in 2D transition metal dichalcogenides using a first-principles approach. Specifically, 2D TMDs, i.e., monolayer MX$_{2}$ (M=Mo and W; X=S and Se) material are investigated. The scattering rates are calculated using Density Functional Theory (DFT) and Density Functional Perturbation Theory (DFPT) and intrinsic electron/hole-mobility is obtained though full band Monte Carlo carrier transport simulation. Then, the parameters for the deformation potential model are extracted from the first principle's transport studies for practical purposes. Our calculation reveals WS$_2$ has the largest mobility among the investigated TMDs. At room temperature, the electron mobility of WS$_2$ is 300 cm$^2$/Vs, which is smaller than that of usual bulk semiconductor. Contrary to this, the hole mobility of WS$_2$ turns out to be over than 800 cm$^2$/Vs, which is even higher than that of bulk silicon, which provides a good opportunity of high-performance pMOSFET. Our work examines the electronic transportation property of 2D TMD material from first-principles approach and demonstrates the importance of electron/hole-phonon scattering in those materials and provides optimal channel material for future field effect transistor. [Preview Abstract] |
Friday, March 7, 2014 9:00AM - 9:12AM |
Y51.00006: Electrical Transport and Photoresponse of Field-Effect Transistors Based on Two-Dimensional Metal-Layered Materials Ming-Wei Lin, Ivan Kravchenko, Jason Fowlkes, Jiaqiang Yan, Xufan Li, Alexander Puretzky, Christopher Rouleau, David Mandrus, David Geohegan, Kai Xiao High performance field effect transistors based on exfoliated two-dimensional (2D) layered materials of transition metal dichalcongenides (TMDCs) such as MoS$_{2}$, WSe$_{2}$ and MoSe$_{2}$ have been demonstrated. The electrical transport measurements show that the mobility is associated with the thickness and temperature for mono- and few-layered 2D materials. Besides, these 2D materials are demonstrated highly sensitive to the light, providing the potential applications for photodetectors or optoelectronic devices. In addition, the thickness dependence of noise measurement for these 2D materials will also be discussed. [Preview Abstract] |
Friday, March 7, 2014 9:12AM - 9:24AM |
Y51.00007: Dielectric and Conductivity Mapping of Few-Layer Metal Chalcogenides Keji Lai, Di Wu, Yingnan Liu, Yuan Ren, Min Lin, Hailin Peng, Ariel Ismach, Rudresh Ghosh, Rodney Ruoff A novel microwave impedance microscope was used to spatially map the local dielectric constant and conductivity of few-layered metal chalcogenides without the need of contact electrodes. For phase-change In$_{2}$Se$_{3}$ nanoplates grown on mica substrates, our results showed a sudden drop of permittivity from the bulk value for thicknesses below 5 layers and strong dielectric inhomogeneity around 4 and 5 layers. For CVD-grown MoS$_{2}$ flakes on SiO$_{2}$/Si wafers, we observed highly conductive localized regions within monolayer islands. These regions, which can be imaged by scanning electron microscopy and atomic force microscopy, show enhanced Raman signals and PL signal quenching. Continued imaging effort is expected to shed some light on the growth mechanism and electron physics of these quasi-2D chalcogenides. [Preview Abstract] |
Friday, March 7, 2014 9:24AM - 9:36AM |
Y51.00008: A comparison of MoSe$_{2}$ field-effect transistors on SiO$_{2}$ and parylene-C substrates: possible surface polar phonon effects Bhim Chamlagain, Qing Li, Minghu Pan, Tugeng Hong, Hsuen-Jen Chuang, Meeghage Perera, Yong Xu, Di Xaio, Nirmal Ghimire, Jiaqiang Yan, David Mandrus, Zhixian Zhou We report the fabrication and electrical characterization of high quality MoSe$_{2}$ field-effect transistors fabricated on both SiO$_{2}$ and parylene-C substrates. Multilayer MoSe$_{2}$ on parylene-C shows a significantly higher room temperature mobility of 100 cm$^{2}$V$^{-1}$s$^{-1} -$ 160 cm$^{2}$V$^{-1}$s$^{-1}$ than that on SiO$_{2}$ ($\approx $50 cm$^{2}$V$^{-1}$s$^{-1})$. Our variable temperature transport measurements indicate that the mobility of MoSe$_{2}$ devices on both SiO$_{2}$ and parylene-C increases to $\approx $ 500 cm$^{2}$V$^{-1}$s$^{-1}$ as the temperature decreases to below 100 K, with the mobility of MoSe$_{2}$ on SiO$_{2}$ increasing more rapidly. We attribute the observed difference in mobility and its temperature dependence between MoSe$_{2}$ on SiO$_{2}$ and on parylene-C primarily to the surface polar optical phonon scattering in the SiO$_{2}$ substrate, which is absent in parylene-C. [Preview Abstract] |
Friday, March 7, 2014 9:36AM - 9:48AM |
Y51.00009: ABSTRACT WITHDRAWN |
Friday, March 7, 2014 9:48AM - 10:00AM |
Y51.00010: Charge Scattering and Mobility in Atomically Thin Semiconductors Nan Ma, Debdeep Jena The electron transport properties in atomically thin semiconductors have attracted intense interest. In this work, we study the scattering mechanisms that limiting the mobility of such semiconductors. The effects of the dielectric environments are also evaluated. We find that high-K dielectrics increase the charged-impurity-limited mobility, but weaken the free-carrier screening. The strong remote optical phonon scattering from high-K dielectrics severely decrease the high-temperature mobility. From a comparative study of different scattering mechanisms, we find that all current reported measured mobilities (around 100 cm$^{\mathrm{2}}$/Vs) are dominated by charged impurity scattering. When the impurity densities are reduced, remote phonon scattering determines the room-temperature mobility upper-limits. The mobilities achieved till date are far below the intrinsic potential in these materials. The truly intrinsic mobility over 10,000 cm$^{\mathrm{2}}$/Vs at room temperature can only be achieved in ultraclean suspended samples. Among the commonly used dielectrics, AlN and BN offer the best compromise if a high mobility over 1000 cm$^{\mathrm{2}}$/Vs and a high gate capacitance are simultaneously desired, as is the case in field effect transistors. [Preview Abstract] |
Friday, March 7, 2014 10:00AM - 10:12AM |
Y51.00011: Conductivity and Carrier Dynamics in Multilayer Molybdenum Disulphide (MoS$_{2})$ Measured by THz Time-Domain Spectroscopy Jared Strait, Parinita Nene, Farhan Rana We present results on the ultrafast carrier dynamics and the frequency-dependent conductivity of multilayer MoS$_{2}$ using optical-pump terahertz-probe spectroscopy with sub-ps time resolution. Measurements done at various temperatures reveal that the photoexcited conductivity is well-described by the Drude model, with a mobility of 300 cm$^{2}$/V-s at 300 K increasing to 5200 cm$^{2}$/V-s at 30 K. We find that the Drude scattering rate increases linearly with temperature, which we attribute to phonon-dominated scattering. Various time scales are observed in the dynamics of photoexcited carriers. Immediately after photoexcitation, the conductivity takes $\sim$ 1-2 ps to reach its maximum value, as carriers undergo intraband relaxation, and then decays as they recombine. During the first 100 ps after photoexcitation, we observe $\sim$ 1/ns recombination rates with a linear dependence on the carrier density. Recombination rates become smaller and independent of carrier density as time progresses. Complete transients can last over tens of ns. Carrier dynamics are found to be temperature dependent, becoming faster at higher temperatures. We will present physical models that explain our data. [Preview Abstract] |
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