Emerging thermal metrology for ultra-wide bandgap semiconductor devices

Ultrawide bandgap (UWBG) semiconductor materials, such as β−Ga2O3 (gallium oxide), AlN (aluminum nitride), AlxGa1−xN (AlGaN), and diamond, have emerged as essential candidates for components in high-power, high-frequency applications due to their superior electronic properties. However, with the exception of diamond and AlN, these materials present unique thermal management challenges, primarily because of their low thermal conductivities that are incapable of managing the demand for high power densities. Therefore, novel thermal management approaches that feature new device architectures are needed to prevent excessively high peak temperatures in UWBG devices. In parallel, accurate device-level thermal characterization (with high spatial/temporal resolution) is crucial to verify and optimize these designs with an overall goal to improve device performance and reliability. This paper discusses current thermal metrology techniques used for UWBG semiconductor devices covering: optical methods (Raman and thermoreflectance); electrical methods (gate resistance thermometry); and scanning probe methods (scanning thermal microscopy). More specifically, the steady-state and transient capability of each thermal metrology is explored and the limitation of each technique is highlighted. Finally, this perspective outlines potential advances in transient thermoreflectance imaging including a hyperspectral approach for nitride based heterostructures and a sub-bandgap excitation technique for gallium oxide based electronics. Additionally, the development of a future thermoreflectance microscope is presented. This microscope features high optical transmission, in the deep ultra violet wavelength range, for near bandgap thermoreflectance imaging of UWBG devices.