Nanoscale thermal processes in devices

对于当前和新兴的电子设备来说，热管理是一个重要的问题，它们越来越多地以高功率密度运行，并将功率耗散到越来越小的体积中。此外，设备越来越多地由众多材料界面组成，这强烈影响了热量的流动，并导致在描述热量如何从设备传递时，器件材料的导热系数的文献值越来越无关紧要。研究小组将利用最近开发的一种工具，以前所未有的空间分辨率绘制设备内的温度，研究材料结等基本设备构建块的散热问题，以及高功率晶体管和激光器等关键技术。根据测量的温度曲线，该团队将制定通用设计原则，以更好地管理设备中的热量，这可以为许多设备类型提供更好的性能和可靠性，包括发光二极管、激光器、晶体管、太阳能电池和热电发电机/冷却器。从广泛的角度来看，这些进步将有助于移动电子、通信系统和能量收集系统等技术平台的性能。这项工作还将通过直接的研究活动和开发的课程材料，培养本科生和研究生关于器件物理学、纳米尺度能量输运和固态物理学的主题。此外，该团队将让高中生和少数族裔参与与能源和电子设备相关的科学和工程活动。该项目的目标是使用高分辨率热测量与耦合电子/声子模型相结合，以获得对控制器件中纳米级热输运过程的基本见解。这样的设备越来越多地在高场和高功率密度下工作，导致电子、光学声子和声学声子系统经常彼此失去热平衡。此外，材料界面可以强烈地影响声子散射和声子色散。虽然非平衡对纳米器件（特别是硅场效应管）加热的影响已经进行了十多年的计算研究，但由于缺乏能够以纳米分辨率直接探测温度场的仪器，大多数提出的模型和其中做出的大量假设仍然未经实验验证。研究组将利用最近开发的超高真空扫描热显微镜，以前所未有的空间分辨率（10纳米）和温度分辨率（15 mK）探测温度场。该工具将首次提供对偏置器件温度场的实验洞察，并与电子和声子输运模型相结合，将揭示器件结和热点处电子-声子和声子-声子耦合的本质。该研究将首先探测偏置单异质结和同质结，然后扩展到p-n二极管、二极管激光器和hemt等原型设备。所提出的工作所获得的理解将使器件工程师能够更好地分析器件散热的瓶颈，设计器件内的热电制冷，以及更好地设计声子辅助隧道和非辐射跃迁等过程中的电子-声子散射。

Thermal management is a significant concern for current and emerging electronic devices, which increasingly operate with high power densities and dissipate power into ever-smaller volumes. Furthermore, devices are increasingly composed of numerous material interfaces, which strongly impact the flow of heat and cause literature values of a device material's thermal conductivity to be more and more irrelevant when describing how heat is transferred from the device. Using a recently developed tool that can map the temperature in a device with unprecedented spatial resolution, the research team will study heat dissipation in fundamental device building blocks such as material junctions as well as critical technologies such as high-power transistors and lasers. From measured temperature profiles, the team will develop general design principles for better managing heat in devices, which can provide better performance and better reliability for numerous device types including light-emitting diodes, lasers, transistors, solar cells, and thermoelectric generators/coolers. From a broad perspective, these advances will aid the performance of technology platforms such as mobile electronics, communications systems, and energy harvesting systems. This work will also train undergraduate and graduate students on the topics of device physics, nanoscale energy transport, and solid state physics, through direct research activities as well as developed course materials. Furthermore, the team will engage high school students and underrepresented minorities in science and engineering activities related to energy and electronic devices.The goal of this project is to use high-resolution thermal measurements in conjunction with coupled electron/phonon models to obtain fundamental insight into the processes that govern nanoscale thermal transport in devices. Such devices increasingly operate with high fields and high power densities, leading to electron, optical phonon, and acoustic phonon systems that are often out of thermal equilibrium with each other. Furthermore, material interfaces can strongly impact phonon scattering and phonon dispersion. While the implications of non-equilibrium on heating in nanoscale devices (especially Si FETs) have been studied computationally for over a decade, most of the proposed models and the large number of assumptions made within them remain experimentally untested due to a lack of instruments that can directly probe temperature fields with nanometer resolution. The research team will utilize an ultra-high vacuum scanning thermal microscope they have recently developed that is capable of probing temperature fields with unprecedented spatial resolution (10 nm) and temperature resolution (15 mK). This tool will provide the first experimental insight into the temperature fields in biased devices, and in conjunction with electron and phonon transport models will reveal the nature of electron-phonon and phonon-phonon coupling at device junctions and hotspots. The study will begin by first probing biased single heterojunctions and homojunctions, and will then expand to prototypical devices such as p-n diodes, diode lasers, and HEMTs. The understanding gained by the proposed work will enable device engineers to better analyze bottlenecks to device heat dissipation, engineer thermoelectric refrigeration within a device, and better engineer electron-phonon scattering for processes such as phonon-assisted tunneling and nonradiative transitions.