VAlVAg Ohmic contacts to n-AlGaNGaN heterostructures with a thin GaN cap

Silver is studied as a replacement for Au in V- and Ti-based Ohmic contacts to GaN-capped n- Al0.27 Ga0.73 NGaN heterostructures for high electron mobility transistors. An optimized VAlVAg contact provided a low contact resistance of 0.27 mm and specific contact resistance of 1.7× 10-6 cm2, and was much smoother than analogous Au-bearing metallizations. Transmission electron microscopy reveals a very limited reaction of the annealed metallization and semiconductor, leaving the Al0.27 Ga0.73 N layer intact. The majority of the Al0.27 Ga0.73 N interface is contacted by Ag-bearing phases. Silver has a lower work function than Au and facilitates the formation of a low-resistance Ohmic contact.