1,004 research outputs found
Enhanced Carrier Transport by Transition Metal Doping in WS2 Field Effect Transistors
High contact resistance is one of the primary concerns for electronic device
applications of two-dimensional (2D) layered semiconductors. Here, we explore
the enhanced carrier transport through metal-semiconductor interfaces in WS2
field effect transistors (FETs) by introducing a typical transition metal, Cu,
with two different doping strategies: (i) a "generalized" Cu doping by using
randomly distributed Cu atoms along the channel and (ii) a "localized" Cu
doping by adapting an ultrathin Cu layer at the metal-semiconductor interface.
Compared to the pristine WS2 FETs, both the generalized Cu atomic dopant and
localized Cu contact decoration can provide a Schottky-to-Ohmic contact
transition owing to the reduced contact resistances by 1 - 3 orders of
magnitude, and consequently elevate electron mobilities by 5 - 7 times higher.
Our work demonstrates that the introduction of transition metal can be an
efficient and reliable technique to enhance the carrier transport and device
performance in 2D TMD FETs.Comment: Under revie
Determination of key device parameters for short- and long-channel Schottky-type carbon nanotube field-effect transistors
The Schottky barrier, contact resistance and carrier mobility in carbon nanotube (CNT) field-effect transistors (FETs) are discussed in detail in this thesis. Novel extraction methods and definitions are proposed for these parameters. A technology comparison with other emerging transistor technologies and a performance projection study are also presented. A Schottky barrier height extraction method for CNTFETs considering one-dimensional (1D) conditions is developed. The methodology is applied to simulation and experimental data of CNTFETs feasible for manufacturing. Y-function-based methods (YFMs) have been applied to simulation and experimental data in order to extract a contact resistance for CNTFETs. Both extraction methods are more efficient and accurate than other conventional approaches. Practical mobility expressions are derived for CNTFETs covering the ballistic as well as the non-ballistic transport regime which enable a straightforward evaluation of the transport in CNTs. They have been applied to simulation and experimental data of devices with different channel lengths and Schottky barrier heights. A comparison of fabricated emerging transistors based on similar criteria for various application scenarios reveals CNTFETs as promising candidates to compete with Si-based technologies in low-power static and dynamic applications. A performance projection study is suggested for specific applications in terms of the studied design parameters
Highly Quantum-Confined InAs Nanoscale Membranes
Nanoscale size-effects drastically alter the fundamental properties of
semiconductors. Here, we investigate the dominant role of quantum confinement
in the field-effect device properties of free-standing InAs nanomembranes with
varied thicknesses of 5-50 nm. First, optical absorption studies are performed
by transferring InAs "quantum membranes" (QMs) onto transparent substrates,
from which the quantized sub-bands are directly visualized. These sub-bands
determine the contact resistance of the system with the experimental values
consistent with the expected number of quantum transport modes available for a
given thickness. Finally, the effective electron mobility of InAs QMs is shown
to exhibit anomalous field- and thickness-dependences that are in distinct
contrast to the conventional MOSFET models, arising from the strong quantum
confinement of carriers. The results provide an important advance towards
establishing the fundamental device physics of 2-D semiconductors
Opto-Valleytronic Spin Injection in Monolayer MoS2/Few-Layer Graphene Hybrid Spin Valves
Two dimensional (2D) materials provide a unique platform for spintronics and
valleytronics due to the ability to combine vastly different functionalities
into one vertically-stacked heterostructure, where the strengths of each of the
constituent materials can compensate for the weaknesses of the others. Graphene
has been demonstrated to be an exceptional material for spin transport at room
temperature, however it lacks a coupling of the spin and optical degrees of
freedom. In contrast, spin/valley polarization can be efficiently generated in
monolayer transition metal dichalcogenides (TMD) such as MoS2 via absorption of
circularly-polarized photons, but lateral spin or valley transport has not been
realized at room temperature. In this letter, we fabricate monolayer
MoS2/few-layer graphene hybrid spin valves and demonstrate, for the first time,
the opto-valleytronic spin injection across a TMD/graphene interface. We
observe that the magnitude and direction of spin polarization is controlled by
both helicity and photon energy. In addition, Hanle spin precession
measurements confirm optical spin injection, spin transport, and electrical
detection up to room temperature. Finally, analysis by a one-dimensional
drift-diffusion model quantifies the optically injected spin current and the
spin transport parameters. Our results demonstrate a 2D spintronic/valleytronic
system that achieves optical spin injection and lateral spin transport at room
temperature in a single device, which paves the way for multifunctional 2D
spintronic devices for memory and logic applications.Comment: Nano Letters, in pres
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