ENG-SEMICON: Understanding Nanoscale Heat Transport in Wide- and Ultrawide Bandgap Semiconductors Using Novel Deep Ulraviolet Tools

Removing excess heat from electronic devices is essential for energy efficiency, overall performance, reliability, and lifespan. Next-generation electronic devices, including communication systems, electrical vehicles, high-performance computation, and military technologies, will need to operate at much higher frequencies and power levels. Meeting this demand will require new semiconductors materials with capabilities beyond those of silicon and models that can accurately describe the heat flow behavior within complex microelectronics. This project will develop unique measurement tools by harnessing ultraviolet laser pulses to study heat flow in these future semiconductor materials. The results will provide critical information about heat behavior at extremely small size and timescales, which will advance models of heat flow for the semiconductor industry. In addition, the project will encourage undergraduate and graduate students to work closely with industry professionals, which will help educate the future workforce in microelectronics. This project will demonstrate and advance a nondestructive, noncontact ultrafast, deep-ultraviolet transient grating spectroscopy technique to probe phonon-dominated thermal transport in wide- and ultrawide-bandgap thin films and substrates as a function transport length-scale. By coupling the extensive previous work in visible-based transient grating spectroscopy with the high-photon energy and short-wavelength of ultrafast deep-ultraviolet laser pulses, this project will harness these new tools to observe phonon flow over effective transport scales in the sub-100 nm regime with sub-ps temporal precision. Specifically, these results will fill much-needed gaps in the literature on the thermal transport properties of gallium oxides, boron nitride, crystalline diamond, and other materials. More importantly, this project will investigate the exotic behaviors of nanoscale hot spots in these materials induced by highly-nonequilibrium phonon distributions, such as thermal viscous and memory effects that were recently observed in crystalline silicon and germanium. By collaborating closely with state-of-the-art theory, these measurements will provide more insight on the fundamental picture of heat flow in semiconductors and validate new models, such as the mesoscopic hydrodynamic approach, with the capability to predict behavior in complex and multi-scales 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.