Collaborative Research: High-order Phonon Scattering and Highly Nonequilibrium Carrier Transport in Two-dimensional Electronic and Optoelectronic Materials

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Semiconductor research and development over the past several decades have enabled widespread use of electronic devices in society. However, the semiconductor industry is facing significant challenges, such as the difficulty in dissipating the large amount of heat generated in silicon electronic chips. The challenges have motivated the investigation of emerging two-dimensional (2D) electronic materials because of their superior electronic and thermal properties. One representative 2D material is graphene that is made of a single layer of carbon atoms. However, compared to the abundant knowledge of silicon electronics, there is only limited understanding of heat dissipation in 2D electronic materials. Therefore, the goal of this project is to establish an in-depth understanding of the distinctly different heat generation and dissipation processes in 2D materials and devices. The obtained knowledge will be used to develop open-source simulation tools, enhance online courses and classroom instruction, and develop hands-on outreach activities to improve the recruitment and training of a diverse population of next-generation workforce in thermal engineering. The goal of this project is to understand the unique fundamental mechanisms underlying heat generation and conduction processes in emerging 2D electronic and optoelectronic materials, including graphene and transition metal dichalcogenides (TMD). Specifically, three outstanding questions that are relevant to the performance and thermal reliability of 2D electronic and optoelectronic materials will be addressed: (1) the importance of four-phonon scattering processes in graphene and other 2D materials; (2) the length scales for different phonon polarizations and electronic excitations to establish local thermal equilibrium in 2D semiconductors; and (3) the phonon mode conversion and transmission processes across the dimensionally mismatched interfaces between a 2D layer and its 3D support. The questions will be addressed via first principles and atomistic theoretical calculations that resolve the modal scattering and coupling behaviors of phonons and electrons, in conjunction with thermal transport and inelastic light scattering measurements of graphene and TMD. Improved understanding of the three specific questions helps to build the foundation for modeling and controlling heat dissipation processes in 2D materials and devices.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.