Deep-Ultraviolet Thermoreflectance Imaging of Ultra-Wide Bandgap Semiconductor Devices

AlGaN/GaN high electron mobility transistors (HEMTs) have tremendously advanced today’s power electronics and radio frequency (RF) applications. In order to further improve the device performance in terms of higher sheet charge density and/or a kV-range critical electric field, HEMTs based on ultra-wide bandgap (UWBG) semiconductor heterostructures AlScN/GaN and AlGaN/AlGaN have been recently developed.<br/>For these devices to handle the high operational frequencies of 5G and beyond, their physical dimensions must decrease and devices must transmit higher RF signals to counter signal attenuation. Higher power and aggressive scaling translate to extreme operational heat fluxes and thus self-heating, which significantly impacts the device performance and reliability. Therefore, it is crucial to experimentally quantify the temperature profile across the active region of these devices. This will allow to accurately predict the component lifetime and design thermal management solutions.<br/>We have developed a deep-ultraviolet (DUV) thermoreflectance imaging technique that offers the highest spatial resolution among far-field optical methods and allows to directly probe the two-dimensional electron gas (2-DEG) region of UWBG AlScN/GaN and AlGaN-channel HEMTs. This allows to explore the fundamental physics of thermal transport within the UWBG material under high electric field conditions and serves as the first step to the electro-thermal co-design of emerging UWBG device technologies.