V ∕ Al ∕ V ∕ Ag Ohmic contacts to n-AlGaN∕GaN 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-Al0.27Ga0.73N∕GaN heterostructures for high electron mobility transistors. An optimized V∕Al∕V∕Ag contact provided a low contact resistance of 0.27Ωmm and specific contact resistance of 1.7×10−6Ωcm2, 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 Al0.27Ga0.73N layer intact. The majority of the Al0.27Ga0.73N 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.