Notice
and Invitation
Oral Defense of
Doctoral Dissertation
Department of
Electrical and Computer Engineering
Volgenau School
of Engineering, George Mason University
Deepak
K Sharma
Bachelor of
Science, Visvesvaraya Technological University
Master of
Science, George Mason University
Friday, April 11th,
2014
10:30 AM to
12:30 PM
The Nguyen
Engineering Building, Room 3507
All are invited
to attend.
Committee
Qiliang Li,
Dissertation Director
Dimitris E. Ioannou
Rao V. Mulpuri
Yuri Mishin
Abhishek Motayed
Albert V.
Davydov
Electrical
Transport and Low Frequency Noise in Reduced Dimension
Field-effect Transistors
The
dimensional scaling of Complementary Metal-Oxide-Semiconductor
devices for
better performance cannot continue indefinitely. One of the
predominant factors
is the increasing statistical fluctuation with the down-scaling
dimensions. As
the dimension shrinks, the number of electrons within the device
decreases.
Consequently, statistical fluctuation in the number becomes an
increasing
fraction of the total electrons, limiting device performance,
and makes circuit
design more challenging.
Low
frequency noise (LFN) is one of the major sources of statistical
fluctuation in
materials. My thesis presents many key revelations associated
with LFN and
electric transport in Field-effect Transistors (FETs) made of
(reduced
dimension geometry) materials like Silicon Nanowire (SiNW) and
2-Dimensional Molybdenum
disulfide (MoS2).
First,
I designed and installed precise noise measurement setup. This
is crucial
because accurate device noise measurement can be affected by
many other
sources, such as amplifiers, cables, connectors, AC power
supplies, etc.
Second,
I fabricated and tested SiNW FETs. Temperature-dependent
(77K-300K) LFN
measurement revealed the presence of generation-recombination
related
Lorentzian-type peaks along with 1/f
-type noise in these SiNW FETs. I have successfully detected the
electrically
active deep-levels at very low concentration which are
associated with Gold and
Nickel metals in the SiNWs using LFN measurements.
Third,
I performed temperature dependent electrical transport and LFN
measurement on
monolayer-layer MoS2 FETs prepared by chemical deposition. The
effect of high-κ
dielectric passivation on the electrical transport properties
revealed key
aspects related to activation energy. The observed channel
current noise
revealed different trapping states in passivated devices when
compared to the
devices without high-κ dielectric passivation.
Fourth,
I studied electrical transport LFN in FETs consisting of
different number of
MoS2 layers. Based on our comparative analysis of both
electrical transport and
LFN on the MoS2 devices with different number of layers, we
found that devices
containing 4 to 7 layers may provide the optimum FET
performance. Devices with
thick MoS2 suffers from low mobility values, weak dependence of
channel current
on gate voltage and increase in normalized LFN value, while
conduction in mono-
and few-layer devices is affected by surface states at
oxide-semiconductor
interface and therefore, shows much higher LFN.
In
summary, my thesis has presented a detailed study on the
electrical transport
and low-frequency noise of nanoelectronic devices based on
reduced dimensional
materials. The findings in this thesis will play a significant
role in the
optimization of reduced dimension devices for future generation
electronics.