The Woodruff School

SUMMARY

As the device dimension scales down and power dissipation increases in the electronic devices, the inefficient thermal management becomes challenging for the performance and reliability. Phonons are expected to be the dominant energy carriers for the thermal transport in the nano-electronic materials such as Graphene, 2D transition metal dichalcogenides (TMDs) and ultra-wide bandgap semiconductors (UWBGS), such as GaN and β-Ga2O3. Due to the low thermal boundary conductance at the interfaces, and the defect-induced phonon scatterings in these materials, the heat dissipation becomes even worse in their micro- and nano-electronic devices. A fundamental understanding of phonon transport properties of these nano-electronic materials considering the influence of interfaces, boundaries, and defects is of great importance for improving reliability and energy efficiency for the nano-electronics. In this study, we developed an atomistic framework based on the first-principle Density Functional Theory (DFT) and the Atomistic Green’s Function (AGF) to investigate the thermal transport across the vertically stacked 2-D semiconductor/substrate interfaces. The study deciphers the inherent connection among the interfacial electronic structure, charge transfer, the phonon distribution and transmission, and thermal boundary conductance at the interfaces. Furthermore, we used DFT along with the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of these materials. The model for estimating the influence of boundary and vacancy defects on the thermal conductivity is developed by considering contributions of phonon boundary scattering. Furthermore, a parameter-free DFT model is developed to investigate the influence of different types of the defects on the thermal conductivity and to validate the empirical model of defects. Our findings in this study will provide insights to engineer the interfaces for effective thermal management. They will also help in understanding the defect-induced phonon transport mechanism in electronic semiconducting materials and provide reliable empirical models to estimate the material properties considering the influence of defects, which could be used for the future design of electronics.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Zhequan Yan

TIME:	Tuesday, August 21, 2018, 3:00 p.m.

PLACE:	MRDC Building, 4404

TITLE:	The Role of Interfaces and Defects on the Thermal Transport in Nano-Electronic Semiconducting Materials

COMMITTEE:	Dr. Satish Kumar, Chair (ME) Dr. Zhuomin Zhang (ME) Dr. Matthew McDowell (ME & MSE) Dr. Eric Vogel (MSE) Dr. Seung Soon Jang (MSE)

SUMMARY As the device dimension scales down and power dissipation increases in the electronic devices, the inefficient thermal management becomes challenging for the performance and reliability. Phonons are expected to be the dominant energy carriers for the thermal transport in the nano-electronic materials such as Graphene, 2D transition metal dichalcogenides (TMDs) and ultra-wide bandgap semiconductors (UWBGS), such as GaN and β-Ga2O3. Due to the low thermal boundary conductance at the interfaces, and the defect-induced phonon scatterings in these materials, the heat dissipation becomes even worse in their micro- and nano-electronic devices. A fundamental understanding of phonon transport properties of these nano-electronic materials considering the influence of interfaces, boundaries, and defects is of great importance for improving reliability and energy efficiency for the nano-electronics. In this study, we developed an atomistic framework based on the first-principle Density Functional Theory (DFT) and the Atomistic Green’s Function (AGF) to investigate the thermal transport across the vertically stacked 2-D semiconductor/substrate interfaces. The study deciphers the inherent connection among the interfacial electronic structure, charge transfer, the phonon distribution and transmission, and thermal boundary conductance at the interfaces. Furthermore, we used DFT along with the phonon Boltzmann transport equation (BTE) to study the phonon transport properties of these materials. The model for estimating the influence of boundary and vacancy defects on the thermal conductivity is developed by considering contributions of phonon boundary scattering. Furthermore, a parameter-free DFT model is developed to investigate the influence of different types of the defects on the thermal conductivity and to validate the empirical model of defects. Our findings in this study will provide insights to engineer the interfaces for effective thermal management. They will also help in understanding the defect-induced phonon transport mechanism in electronic semiconducting materials and provide reliable empirical models to estimate the material properties considering the influence of defects, which could be used for the future design of electronics.