Thermal investigation of quasi-vertical and vertical GaN p–n diodes on sapphire and tungsten substrates

Thermal properties of quasi-vertical GaN-on-sapphire p–n diodes and fully vertical GaN-on-tungsten (W) p–n diodes were investigated. Fully vertical GaN-on-W devices were realized by transferring GaN membranes from sapphire substrates via a laser lift-off process and bonding to a metallic tungsten substrate. Device temperatures were measured using micro-Raman thermography with surface-deposited TiO2 nanoparticles acting as thermometers, and the thermal resistance was determined from the measurement results by 3D thermal simulations. Fully vertical GaN-on-W diodes showed a 3.1× reduction in device thermal resistance compared to quasi-vertical GaN-on-sapphire diodes (21.1 ± 1.5 to 6.8 ± 0.4 mK cm2/W). The extracted thermal resistance is close to simulated models of GaN-on-GaN p–n diodes, validating tungsten as an excellent, thermally stable metallic substrate for GaN-based high-power vertical devices.