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 (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.