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

在过去的几十年里，半导体的研究和发展使电子设备在社会上得到了广泛的使用。然而，半导体行业正面临着重大挑战，例如难以分散硅电子芯片产生的大量热量。这些挑战推动了对新兴的二维电子材料的研究，因为它们具有优异的电子和热性能。一种具有代表性的2D材料是由单层碳原子组成的石墨烯。然而，与硅电子学的丰富知识相比，人们对二维电子材料的散热了解还很有限。因此，该项目的目标是深入了解2D材料和设备中截然不同的热产生和散热过程。所获得的知识将用于开发开放源码模拟工具，加强在线课程和课堂教学，并开展实践外联活动，以改进热工领域多样化下一代劳动力的招聘和培训。该项目的目标是了解新兴的二维电子和光电子材料，包括石墨烯和过渡金属二卤化物(TMD)中独特的产生热和传导过程的基本机制。具体地说，与2D电子和光电子材料的性能和热可靠性相关的三个悬而未决的问题将被解决：(1)四声子散射过程在石墨烯和其他2D材料中的重要性；(2)不同声子极化和电子激发的长度尺度，以建立2D半导体中的局部热平衡；以及(3)2D层和其3D载体之间的声子模转换和传输过程。这些问题将通过第一性原理和原子理论计算来解决，这些计算结合石墨烯和TMD的热输运和非弹性光散射测量来解决声子和电子的模式散射和耦合行为。对这三个具体问题的更好理解有助于为2D材料和设备中的散热过程建模和控制奠定基础。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

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.