Effects of rapid thermal annealing on ohmic contact of AlGaN/GaN HEMTs

Ohmic contacts with Ti/Al/Ti/Au source and drain electrodes on AlGaN/GaN high electron mobility transistors (HEMTs) were fabricated and subjected to rapid thermal annealing (RTA) in flowing N2. The wafer was divided into 5 parts and three of them were annealed for 30 s at 700, 750, and 800 °C, respectively, the others were annealed at 750 °C for 25 and 40 s. Due to the RTA, a change from Schottky contact to Ohmic contact has been obtained between the electrode layer and the AlGaN/GaN heterojunction layer. We have achieved a low specific contact resistance of 7.41 × 10−6 Ωcm2 and contact resistance of 0.54 Ωmm measured by transmission line mode (TLM), and good surface morphology and edge acuity are also desirable by annealing at 750 °C for 30 s. The experiments also indicate that the performance of ohmic contact is first improved, then it reaches a peak, finally degrading with annealing temperature or annealing time rising.