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 N 2. The wafer was divided into 5 parts and three of them were annealed for 30 s at 700, 750, and 800 degrees C, respectively, the others were annealed at 750 degrees 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 x 10(-6) Omega.cm(2) and contact resistance of 0.54 Omega.mm measured by transmission line mode (TLM), and good surface morphology and edge acuity are also desirable by annealing at 750 degrees Cfor 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.