  In this work, single-layer intrinsic and fluorinated graphene were
investigated as gate insertion layers in normally-OFF p-GaN gate HEMTs, which
wraps around the bottom of the gate forming Ti/graphene/p-GaN at the bottom and
Ti/graphene/ SiNx on the two sides. Compared to the Au/Ti/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 {\deg}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 Ti/graphene/p-GaN and Ti/graphene/SiNx
interfaces. This approach is very effective in improving the Ion/Iff ratio and
gate BV of normally-OFF GaN HEMTs.
