Gate Leakage Suppression and Breakdown Voltage Enhancement in p-GaN HEMTs using Metal/Graphene Gates.

In this work, single-layer intrinsic and fluorinated graphene were investigated as gate insertion layers for normally-OFF p-GaN gate HEMTs, which were sandwiched between the Ti/p-GaN and Ti/SiNx. Compared to the metal/p-GaN HEMTs without graphene, the insertion of graphene can increase the ION/IOFF ratios by a factor of 50, increase the VTH by 0.30 V and reduce the off-state gate leakage by 50 times. Additionally, this novel gate structure has better thermal stability. After thermal annealing at 350 degree C, gate breakdown voltage holds at 12.1 V, which is first reported for Schottky gate p-GaN HEMTs. This is considered to be a result of the 0.24 eV increase in Schottky barrier height and the better quality of the graphene/p-GaN and graphene/SiNx interfaces. This approach is very effective in improving the ION/IOFF ratio and gate BV of normally-OFF GaN HEMTs.