Thermal conductivity, anisotropy, and interface resistances of diamond on poly-AlN

Due to their high thermal conductivity, diamond substrates are seen as a way to minimize the thermal resistance present in High Electron Mobility Transistor (HEMT) structures based on GaN. Single-crystal AlN transition layers facilitate the growth of high quality GaN on diamond, but such layers may increase the total thermal resistance of the composite substrate. This manuscript measures the thermal conductivity and interface resistance of a 1.4 µm diamond film on a polycrystalline AlN substrate using picosecond time-domain thermoreflectance (TDTR) and nanosecond thermoreflectance. Varying beam widths are used to extract the thermal conductivity anisotropy of the diamond film.