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*_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 11^th , 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 (MoS_2 ).

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-? 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-? 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.