Reliability Improvement of GaN Devices on Free-Standing GaN Substrates

In order to analyze the influence of different substrates on the performance of metal-insulator- semiconductor AlGaN/GaN high-electron mobility transistors, devices on free-standing GaN (FS-GaN), silicon, and sapphire substrates with similar AlGaN/GaN top layers were fabricated. Compared with Si and sapphire substrates, the devices on the FS-GaN substrate not only achieve remarkable improvement in the direct current characteristics but also have much better thermal stability and can significantly suppress the self-heating effects, where the current density only decreases by 4% with the channel at 48 °C and an ambient of 25 °C. Owing to the lower trap and dislocation densities in the epitaxial layers, the dynamic performance and reliability of the devices on the FS-GaN substrate are also dramatically improved. With an off-state drain bias of 50 V kept for 10 s, the devices on the FS-GaN substrate only suffer a 10% increase in dynamic on resistance, much lower than the devices on the Si and sapphire substrates. In addition, all the devices were exposed to a 3-MeV proton irradiation with a dose of 3 × 10
¹⁴
cm
^-2
. Compared with the devices before radiation treatment, the dynamic on resistance increases by 79% with a 20-V off-state stress for the devices on the FS-GaN substrate, while the increase is over 800% for the other devices. The lower performance degradation for the devices on the FS-GaN substrate indicates a lower displacement damage and better irradiation tolerance.