Analysis of the ohmic contacts of Ti/Al/Ni/Au to AlGaN/GaN HEMTs by the multi-step annealing process

The multi-step rapid thermal annealing process of Ti/Al/Ni/Au can make good ohmic contacts with both low contact resistance and smooth surface morphology for AlGaN/GaN HEMTs. In this work, the mechanism of the multi-step annealing process is analyzed in detail by specific experimental methods. The experimental results show that annealing temperature and time are very important parameters when optimizing the Ti/Al layer for lower resistance and the Ni/Au layer for smooth surface morphology. It is very important for good ohmic contacts to balance the rate of various reactions by adjusting the annealing temperature and time. We obtained a minimum specific contact resistance of 3.22 × 10 −7 Ω·cm 2 on the un-doped AlGaN/GaN structure with an optimized multi-step annealing process.