195 research outputs found
Current Status of Graphene Transistors
This paper reviews the current status of graphene transistors as potential
supplement to silicon CMOS technology. A short overview of graphene
manufacturing and metrology methods is followed by an introduction of
macroscopic graphene field effect transistors (FETs). The absence of an energy
band gap is shown to result in severe shortcomings for logic applications.
Possibilities to engineer a band gap in graphene FETs including quantum
confinement in graphene Nanoribbons (GNRs) and electrically or substrate
induced asymmetry in double and multi layer graphene are discussed. Graphene
FETs are shown to be of interest for analog radio frequency applications.
Finally, novel switching mechanisms in graphene transistors are briefly
introduced that could lead to future memory devices.Comment: 11 pages, 6 figure
Extended papers selected from ESSDERC 2015
This special issue of Solid State Electronics includes 28 papers which have been carefully selected from the best presentations given at the 45th European Solid-State Device Research Conference (ESSDERC 2015) held from September 14–18, 2015 in Graz, Austria. These papers cover a wide range of topics related to the research on solid-state devices. These topics are used also to organize the conference submissions and presentations into 7 tracks: CMOS Processes, Devices and Integration; Opto-, Power- and Microwave Devices; Modeling & Simulation; Characterization, Reliability & Yield; Advanced & Emerging Memories; MEMS, Sensors & Display Technologies; Emerging Non-CMOS Devices & Technologies
Direct Graphene Growth on Insulator
Fabrication of graphene devices is often hindered by incompatibility between
the silicon technology and the methods of graphene growth. Exfoliation from
graphite yields excellent films but is good mainly for research. Graphene grown
on metal has a technological potential but requires mechanical transfer. Growth
by SiC decomposition requires a temperature budget exceeding the technological
limits. These issues could be circumvented by growing graphene directly on
insulator, implying Van der Waals growth. During growth, the insulator acts as
a support defining the growth plane. In the device, it insulates graphene from
the Si substrate. We demonstrate planar growth of graphene on mica surface.
This was achieved by molecular beam deposition above 600{\deg}C. High
resolution Raman scans illustrate the effect of growth parameters and substrate
topography on the film perfection. Ab initio calculations suggest a growth
model. Data analysis highlights the competition between nucleation at surface
steps and flat surface. As a proof of concept, we show the evidence of electric
field effect in a transistor with a directly grown channel.Comment: 13 pages, 6 figure
Growth-Induced Strain in Chemical Vapor Deposited Monolayer MoS2: Experimental and Theoretical Investigation
Monolayer molybdenum disulphide (MoS) is a promising two-dimensional (2D)
material for nanoelectronic and optoelectronic applications. The large-area
growth of MoS has been demonstrated using chemical vapor deposition (CVD)
in a wide range of deposition temperatures from 600 {\deg}C to 1000 {\deg}C.
However, a direct comparison of growth parameters and resulting material
properties has not been made so far. Here, we present a systematic experimental
and theoretical investigation of optical properties of monolayer MoS grown
at different temperatures. Micro-Raman and photoluminescence (PL) studies
reveal observable inhomogeneities in optical properties of the as-grown single
crystalline grains of MoS. Close examination of the Raman and PL features
clearly indicate that growth-induced strain is the main source of distinct
optical properties. We carry out density functional theory calculations to
describe the interaction of growing MoS layers with the growth substrate as
the origin of strain. Our work explains the variation of band gap energies of
CVD-grown monolayer MoS, extracted using PL spectroscopy, as a function of
deposition temperature. The methodology has general applicability to model and
predict the influence of growth conditions on strain in 2D materials.Comment: 37 pages, 6 figures, 10 figures in supporting informatio
Ultra Low Specific Contact Resistivity in Metal-Graphene Junctions via Atomic Orbital Engineering
A systematic investigation of graphene edge contacts is provided.
Intentionally patterning monolayer graphene at the contact region creates
well-defined edge contacts that lead to a 67% enhancement in current injection
from a gold contact. Specific contact resistivity is reduced from 1372
{\Omega}m for a device with surface contacts to 456 {\Omega}m when contacts are
patterned with holes. Electrostatic doping of the graphene further reduces
contact resistivity from 519 {\Omega}m to 45 {\Omega}m, a substantial decrease
of 91%. The experimental results are supported and understood via a multi-scale
numerical model, based on density-functional-theory calculations and transport
simulations. The data is analyzed with regards to the edge perimeter and
hole-to-graphene ratio, which provides insights into optimized contact
geometries. The current work thus indicates a reliable and reproducible
approach for fabricating low resistance contacts in graphene devices. We
provide a simple guideline for contact design that can be exploited to guide
graphene and 2D material contact engineering.Comment: 26 page
Non-invasive Scanning Raman Spectroscopy and Tomography for Graphene Membrane Characterization
Graphene has extraordinary mechanical and electronic properties, making it a
promising material for membrane based nanoelectromechanical systems (NEMS).
Here, chemical-vapor-deposited graphene is transferred onto target substrates
to suspend it over cavities and trenches for pressure-sensor applications. The
development of such devices requires suitable metrology methods, i.e.,
large-scale characterization techniques, to confirm and analyze successful
graphene transfer with intact suspended graphene membranes. We propose fast and
noninvasive Raman spectroscopy mapping to distinguish between freestanding and
substrate-supported graphene, utilizing the different strain and doping levels.
The technique is expanded to combine two-dimensional area scans with
cross-sectional Raman spectroscopy, resulting in three-dimensional Raman
tomography of membrane-based graphene NEMS. The potential of Raman tomography
for in-line monitoring is further demonstrated with a methodology for automated
data analysis to spatially resolve the material composition in micrometer-scale
integrated devices, including free-standing and substrate-supported graphene.
Raman tomography may be applied to devices composed of other two-dimensional
materials as well as silicon micro- and nanoelectromechanical systems.Comment: 23 pages, 5 figure
Maximum illumination control system for photovoltaic panels orientation
The article describes the solar tracker for photovoltaic panels and energy systems based on such devices. The authors introduce the results of calculations of the solar tracker application effectiveness for solar energy systems and the results of the field testing in Tomsk
A Graphene-based Hot Electron Transistor
We experimentally demonstrate DC functionality of graphene-based hot electron
transistors, which we call Graphene Base Transistors (GBT). The fabrication
scheme is potentially compatible with silicon technology and can be carried out
at the wafer scale with standard silicon technology. The state of the GBTs can
be switched by a potential applied to the transistor base, which is made of
graphene. Transfer characteristics of the GBTs show ON/OFF current ratios
exceeding 50.000.Comment: 18 pages, 6 figure
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