A5081174674- Semiconductor materials and devices
- Advancements in Semiconductor Devices and Circuit Design
- Silicon and Solar Cell Technologies
- Semiconductor materials and interfaces
- 2D Materials and Applications
- Graphene research and applications
- Thin-Film Transistor Technologies
- Integrated Circuits and Semiconductor Failure Analysis
- Nanowire Synthesis and Applications
- Silicon Nanostructures and Photoluminescence
- Quantum and electron transport phenomena
- Ferroelectric and Negative Capacitance Devices
- MXene and MAX Phase Materials
- Silicon Carbide Semiconductor Technologies
- Advanced Memory and Neural Computing
- Topological Materials and Phenomena
- Perovskite Materials and Applications
- Electronic and Structural Properties of Oxides
- Magnetic properties of thin films
- Semiconductor Quantum Structures and Devices
- Quantum Dots Synthesis And Properties
- Ion-surface interactions and analysis
- Molecular Junctions and Nanostructures
- Chalcogenide Semiconductor Thin Films
- GaN-based semiconductor devices and materials
The University of Texas at Austin
2016-2025
Translational Health Science and Technology Institute
2021
National Institute of Pharmaceutical Education and Research
2021
Indian Institute of Technology Kanpur
2021
Intel (United States)
2019-2020
University of South Florida
2019-2020
University of Maryland, College Park
2016
New York University
2016
University of Tennessee System
2008-2014
IBM Research - Thomas J. Watson Research Center
2013
Graphene has been attracting great interest because of its distinctive band structure and physical properties. Today, graphene is limited to small sizes it produced mostly by exfoliating graphite. We grew large-area films the order centimeters on copper substrates chemical vapor deposition using methane. The are predominantly single-layer graphene, with a percentage (less than 5%) area having few layers, continuous across surface steps grain boundaries. low solubility carbon in appears help...
We fabricate and characterize dual-gated graphene field-effect transistors using Al2O3 as top-gate dielectric. use a thin Al film nucleation layer to enable the atomic deposition of Al2O3. Our devices show mobility values over 8000 cm2/V s at room temperature, finding which indicates that stack does not significantly increase carrier scattering consequently degrade device characteristics. propose model fit experimental data single value.
We describe the realization of van der Waals (vdW) heterostructures with accurate rotational alignment individual layer crystal axes. illustrate approach by demonstrating a Bernal-stacked bilayer graphene formed using successive transfers monolayer flakes. The Raman spectra this artificial possess wide 2D band, which is best fit four Lorentzians, consistent Bernal stacking. Scanning tunneling microscopy reveals no moiré pattern on graphene, and spectroscopy as function gate voltage constant...
We study the gate voltage induced gap that occurs in graphene bilayers using \textit{ab initio} density functional theory. Our calculations confirm qualitative picture suggested by phenomenological tight-binding and continuum models. discuss enhanced screening of external interlayer potential at small voltages, which is more pronounced calculations, quantify role crystalline inhomogeneity a model self-consistent Hartree calculation.
We demonstrate dual-gated $p$-type field-effect transistors (FETs) based on few-layer tungsten diselenide (WSe$_2$) using high work-function platinum source/drain contacts, and a hexagonal boron nitride top-gate dielectric. A device topology with contacts underneath the WSe$_2$ results in $p$-FETs $I_{ON}$/$I_{OFF}$ ratios exceeding 10$^7$, that remain Ohmic down to cryogenic temperatures. The output characteristics show current saturation gate tunable negative differential resistance....
2D materials have attracted much interest over the past decade in nanoelectronics. However, it was believed that atomically thin layered are not able to show memristive effect vertically stacked structure, until recent discovery of monolayer transition metal dichalcogenide (TMD) atomristors, overcoming scaling limit sub-nanometer. Herein, nonvolatile resistance switching (NVRS) phenomenon hexagonal boron nitride (h-BN), a typical insulator, is reported. The h-BN atomristors studied using...
We demonstrate the growth of thin films molybdenum ditelluride and diselenide on sapphire substrates by molecular beam epitaxy. In situ structural chemical analyses reveal stoichiometric layered film with atomically smooth surface morphologies. Film along (001) direction is confirmed X-ray diffraction, crystalline nature in 2H phase evident from Raman spectroscopy. Transmission electron microscopy used to confirm structure hexagonal arrangement atoms. Temperature-dependent electrical...
To reduce Schottky-barrier-induced contact and access resistance, the impact of charged impurity phonon scattering on mobility in devices based 2D transition metal dichalcogenides (TMDs), considerable effort has been put into exploring various doping techniques dielectric engineering using $high-\kappa$ oxides, respectively. The goal this work is to demonstrate a that serves as an effective n-type charge transfer dopant monolayer (ML) molybdenum disulfide ($MoS_{2}$). Utilizing amorphous...
We report the fabrication and device characteristics of exfoliated, few-layer, dual-gated ReS2 field effect transistors (FETs). The FETs display n-type behavior with a room temperature Ion/Ioff 105. Many devices were studied maximum intrinsic mobility 12 cm2·V–1·s–1 at 26 77 K. Cr/Au-ReS2 contact resistance determined using transfer length method is gate-bias dependent ranges from 175 kΩ·μm to 5 kΩ·μm, shows an exponential dependence on back-gate voltage indicating Schottky barriers source...
Abstract The ability to scale two-dimensional (2D) material thickness down a single monolayer presents promising opportunity realize high-speed energy-efficient memristors. Here, we report an ultra-fast memristor fabricated using atomically thin sheets of 2D hexagonal Boron Nitride, exhibiting the shortest observed switching speed (120 ps) among memristors and low energy (2pJ). Furthermore, study dynamics these ultra-short (120ps-3ns) voltage pulses, frequency range that is highly relevant...
The role of silicon hydride species in the photoluminescence intensity behavior porous Si has been studied. surfaces luminescent samples were converted to a predominate SiH termination using remote H plasma. as-passivated then immersed various concentrations hydrofluouric solutions regulate recovery SiH2 on surface. Photoluminescence measurements and transmission Fourier-transform infrared spectroscopy have shown that predominant monohydride (SiH) results weak photoluminescence. In contrast,...
We propose a new type of graphene-based transistor intended to allow lower voltage, power operation than possible with complementary metal-oxide-semiconductor (CMOS) field-effect transistors. Increased energy efficiency is not only important for its own sake, but also necessary continued device scaling and the resulting increase in computational CMOS-like logic circuits. describe basic structure physics predicted current-voltage characteristics. Advantages over CMOS terms voltage are discussed.
We demonstrate gate-tunable resonant tunneling and negative differential resistance in the interlayer current–voltage characteristics of rotationally aligned double bilayer graphene heterostructures separated by hexagonal boron nitride (hBN) dielectric. An analysis heterostructure band alignment using individual layer densities, along with experimentally determined chemical potentials indicates that resonance occurs when energy bands two are aligned. discuss dependence on hBN thickness, as...
Flexible synthesized MoS2 transistors are advanced to perform at GHz speeds. An intrinsic cutoff frequency of 5.6 is achieved and analog circuits realized. Devices mechanically robust for 10,000 bending cycles.
Owing in part to scaling challenges for metal oxide semiconductor field-effect transistors (MOSFETs) and complementary (CMOS) logic, the industry is placing an increased emphasis on emerging materials devices that may provide improved MOSFET performance beyond 22 nm node, or novel functionality for, e.g. ‘beyond CMOS’ devices. Graphene, with its electron–hole symmetric band structure high carrier mobilities thermal velocities, one such material has garnered a great deal of interest both...
We study the magnetotransport properties of high-mobility holes in monolayer and bilayer WSe_{2}, which display well defined Shubnikov-de Haas (SdH) oscillations, quantum Hall states high magnetic fields. In both mono- SdH oscillations occur predominantly at even filling factors, evincing a twofold Landau level degeneracy. The Fourier transform analysis WSe_{2} reveals presence two subbands localized top or bottom layer, as negative compressibility. From temperature dependence we determine...
We report on the gigahertz radio frequency (RF) performance of chemical vapor deposited (CVD) monolayer MoS2 field-effect transistors (FETs). Initial DC characterizations fabricated FETs yielded current densities exceeding 200 μA/μm and maximum transconductance 38 μS/μm. A contact resistance corrected low-field mobility 55 cm2/(V s) was achieved. Radio were in ground–signal–ground (GSG) layout, standard de-embedding techniques applied. Operating at peak transconductance, we obtain...
Atomically thin molybdenum disulfide (MoS2), a member of the transition metal dichalcogenide (TMDC) family, has emerged as prototypical two-dimensional (2D) semiconductor with multitude interesting properties and promising device applications spanning all realms electronics optoelectronics. While possessing inherent advantages over conventional bulk semiconducting materials (such Si, Ge III-Vs) in terms enabling ultra-short channel and, thus, energy efficient field-effect transistors (FETs),...
We show that in crystalline insulators, space group symmetry alone gives rise to a topological classification based on the discretization of electric polarization. Using ${C}_{3}$ rotational as an example, we first prove polarization is discretized into three distinct classes, i.e., it can only take inequivalent values. then these classes are topologically distinct. Therefore, ${Z}_{3}$ exists, with class index. A concrete tight-binding model derived demonstrate phase transition....
We demonstrate the synthesis of large-area graphene on Co, a complementary metal-oxide-semiconductor (CMOS)-compatible metal, using acetylene (C(2)H(2)) as precursor in chemical vapor deposition (CVD)-based method. Cobalt films were deposited SiO(2)/Si, and influence Co film thickness monolayer growth was studied, based solubility C Co. The surface area coverage observed to increase with decreasing thickness. A thorough Raman spectroscopic analysis reveals that films, grown an optimized...
Transition metal dichalcogenides are of interest for next generation switches, but the lack low resistance electron and hole contacts in same material has hindered development complementary field-effect transistors circuits. We demonstrate an air-stable, reconfigurable, monolayer MoTe2 transistor encapsulated hexagonal boron nitride, using electrostatically doped contacts. The introduction a multigate design with prepatterned bottom allows us to independently achieve contact threshold...
Adsorption of organic molecules passivates defect states on single-layer MoS 2 via charge transfer.
Non-volatile resistive switching (NVRS) is a widely available effect in transitional metal oxides, colloquially known as memristors, and of broad interest for memory technology neuromorphic computing. Until recently, NVRS was not other dichalcogenides (TMDs), an important material class owing to their atomic thinness enabling the ultimate dimensional scaling. Here, various monolayer or few-layer 2D materials are presented conventional vertical structure that exhibit NVRS, including TMDs (MX2...
One of the most fascinating properties molybdenum disulfide (MoS2) is its ability to be subjected large amounts strain without experiencing degradation. The potential MoS2 mono- and few-layers in electronics, optoelectronics, flexible devices requires fundamental understanding their as a function strain. While previous reports have studied mechanically exfoliated flakes, tensile experiments on chemical vapor deposition (CVD)-grown few-layered not been examined hitherto, although CVD state...