Electrical Comparison of Ta/Ti/Al/Mo/Au and Ti/Al/Mo/Au Ohmic Contacts on Undoped GaN HEMTs Structure with AlN Interlayer

A significant improvement of contact transfer resistance on undoped GaN/AlGaN/AlN (10 Å)/GaN high electron mobility transistor (HEMT) structure was demonstrated using a Ta/Ti/Al/Mo/Au metallization scheme compared to a Ti/Al/Mo/Au metallization scheme. A contact resistance as low as 0.16 ± 0.03 ohm-mm was achieved by rapid thermal annealing of evaporated Ta (125 Å)/Ti (150 Å)/Al (900 Å)/Mo(400 Å)/Au(500 Å) metal contact at 700 °C for 1 min followed by 800 °C for 30 sec in a N₂ ambient. An excellent edge acuity was also demonstrated for the annealed Ta/Ti/Al/Mo/Au ohmic contacts.