6 research outputs found
Strong interfacial exchange field in the graphene/EuS heterostructure
Exploiting 2D materials for spintronic applications can potentially realize
next-generation devices featuring low-power consumption and quantum operation
capability. The magnetic exchange field (MEF) induced by an adjacent magnetic
insulator enables efficient control of local spin generation and spin
modulation in 2D devices without compromising the delicate material structures.
Using graphene as a prototypical 2D system, we demonstrate that its coupling to
the model magnetic insulator (EuS) produces a substantial MEF (> 14 T) with
potential to reach hundreds of Tesla, which leads to orders-of-magnitude
enhancement in the spin signal originated from Zeeman spin-Hall effect.
Furthermore, the new ferromagnetic ground state of Dirac electrons resulting
from the strong MEF may give rise to quantized spin-polarized edge transport.
The MEF effect shown in our graphene/EuS devices therefore provides a key
functionality for future spin logic and memory devices based on emerging 2D
materials in classical and quantum information processing
III-V Nanowire Hetero-junction Tunnel FETs integrated on Si
In the last decade the power consumption of electronic devices has increased for both static and active components. Following the Dennard's scaling rule, as long as the transistor sizes are reduced then the supply voltage (VDD) can also be scaled in order to increase the area density and maintain or improve the performances. However, scaling VDD and thus shifting the threshold voltage (Vth) of 60mV in a metal-oxide semiconductor field-effect transistor (MOSFET) increases the OFF state current (Ioff ) by a factor of 10 in the ideal case. The reason for this is that the inverse subthreshold slope (SS) in an ideal MOSFET is limited by the thermionic emission of electrons over a potential barrier, which has an intrinsic physical limit of 60mV/decade. To overcome this limit, novel device concepts have been proposed and the tunnel field-effect transistor (TFET) is one of the most promising because it resembles a MOSFET and should enable to achieve sub-60mV/dec SS, low Ioff and small VDD. The aim of this thesis is to investigate the potential of TFETs by the fabrication and characterization of InAs/Si as p-channel and InAs/GaSb as n-channel device for a complementary TFET technology. III-V nanowires are grown via metal-organic chemical vapor deposition (MOCVD) and are integrated on Si(100) substrates using a novel technique called template-assisted selective epitaxy (TASE), which enables the fabrication of vertical and lateral III-V hetero-structure TFETs. Sub-40nm nanowire cross-section InAs/Si p-TFETs and InAs/GaSb n-TFETs in-plane on Si are demonstrated for the first time. The InAs/Si p-TFETs exhibit state-of-the art performances with an ON state current (Ion) of 4uA/um at VGS=VDS=-0.5V, ON/OFF ratio of 1x10E5 with SSavg of 70-80mV/dec at room temperature. The InAs/GaSb n-TFETs have an order of magnitude larger Ion but the SS is limited by the non-optimized gate-stack on InAs channel and by the depletion of the undoped GaSb source. Different operation regimes of TFETs are investigated by temperature-dependent measurements,Wentzel-Kramers-Brillouin (WKB) modeling and TCAD simulations, indicating that the switching region for InAs/Si is dominated by the presence of traps at the hetero-junction. The abruptness of the band-edges in InAs/GaSb is studied by the extraction of the conductance slope in fabricated p-n and p-i-n tunnel diodes
Strong interfacial exchange field in the graphene/EuS heterostructure
\u3cp\u3eExploiting 2D materials for spintronic applications can potentially realize next-generation devices featuring low power consumption and quantum operation capability. The magnetic exchange field (MEF) induced by an adjacent magnetic insulator enables efficient control of local spin generation and spin modulation in 2D devices without compromising the delicate material structures. Using graphene as a prototypical 2D system, we demonstrate that its coupling to the model magnetic insulator (EuS) produces a substantial MEF (>14 T) with the potential to reach hundreds of tesla, which leads to orders-of-magnitude enhancement of the spin signal originating from the Zeeman spin Hall effect. Furthermore, the new ferromagnetic ground state of Dirac electrons resulting from the strong MEF may give rise to quantized spin-polarized edge transport. The MEF effect shown in our graphene/EuS devices therefore provides a key functionality for future spin logic and memory devices based on emerging 2D materials in classical and quantum information processing.\u3c/p\u3
High-Mobility GaSb Nanostructures Cointegrated with InAs on Si
GaSb nanostructures
integrated on Si substrates are of high interest
for p-type transistors and mid-IR photodetectors. Here, we investigate
the metalorganic chemical vapor deposition and properties of GaSb
nanostructures monolithically integrated onto silicon-on-insulator
wafers using template-assisted selective epitaxy. A high degree of
morphological control allows for GaSb nanostructures with critical
dimensions down to 20 nm. Detailed investigation of growth parameters
reveals that the GaSb growth rate is governed by the desorption processes
of an Sb surface layer and, in turn, is insensitive to changes in
material transport efficiency. The GaSb crystal structure is typically
zinc-blende with a low density of rotational twin defects, and even
occasional twin-free structures are observed. Hall/van der Pauw measurements
are conducted on 20 nm-thick GaSb nanostructures, revealing high hole
mobility of 760 cm<sup>2</sup>/(V s), which matches literature values
for high-quality bulk GaSb crystals. Finally, we demonstrate a process
that enables cointegration of GaSb and InAs nanostructures in close
vicinity on Si, a preferred material combination ideally suited for
high-performance complementary III–V metal-oxide-semiconductor
technology