The role of interfaces and defects on the thermal transport in nano-electronic semiconducting materials
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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 semiconducting 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 electronic materials considering the influence of interfaces, boundaries, and defects is of high importance for improving reliability and energy efficiency of their electronic devices. In this work, the phonon transport at the interface of vertically stacked graphene and h-BN heterostructures is investigated using first-principles density functional theory (DFT) and atomistic Green’s function (AGF) simulations. The frequency and wave-vector dependent phonon transmission function is computed. Results indicate distinct stacking-dependent thermal boundary conductance (TBC) features for the graphene/h-BN interfaces. In addition, the role of interfacial electronic properties on the phonon transport in monolayer MoS2 adsorbed on metal substrates (Au and Sc) is studied using the DFT and AGF methods. The study reveals that the different degree of orbital hybridization and electronic charge distribution between MoS2 and metal substrates play a significant role in determining the overall phonon-phonon coupling and phonon transmission. The findings demonstrate the inherent connection among the interfacial electronic structure, the phonon distribution, and TBC, which will help in understanding the mechanism of phonon transport at the MoS2/metal interfaces. Another part of this study is investigating the phonon transport properties of electronic materials, such as MoSe2 and β-Ga2O3, under the influence of doping and defects using DFT along with the phonon Boltzmann transport equation (BTE) simulation. The model for estimating the influence of vacancy defects on the thermal conductivity is developed by considering contributions of different types of the defect-induced phonon scatterings. The influence of different types of the defects on the thermal conductivity is studied using the first-principles DFT, considering supercell with defects, which is a parameter-free model. The findings help us understand how the vacancy-induced phonon states impact the mechanism of phonon transport of MoSe2. Furthermore, a modified empirical model of defects is developed in this study which is in better agreement of the parameter-free DFT simulation results. The results from this work will 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.