Formation of ohmic contacts to n-AlxGa1-xN:Si layers with a high aluminum content

The paper describes the results of optimizing rapid thermal annealing (RTA) of ohmic contacts to AlGaN:Si layers with a high aluminum content (70 mol%) and various electron concentration. The contact characteristics were  measured using the transmission line method (TLM). It has been found that for highly doped Al_0.7Ga_0.3N:Si layers (>10¹⁸cm⁻³), the RTA annealing of Ti(25nm)/Al(80nm)/Ti/Au contact at a temperature 900 °C for 60 s makes it possible to obtain the minimum contact resistance of 8 Ω×mm and specific contact resistivity of 9×10⁻⁴ Ω·cm² with high uniformity over the surface of a 2-inch substrate. For lightly doped Al_0.7Ga_0.3N:Si layers (<10¹⁷ cm⁻³), almost the same contact characteristics can be achieved at a higher RTA temperature of about 1000 °C and an increase in the thickness of the Al contact layer to 250 nm.