Low resistance ohmic contacts to p-type GaN and AlGaN

We report the influence of surface treatment, annealing temperature tend metal bilayer thickness on the specific contact resistance (rho(c)) of Au/Ni ohmic contacts to p-GaN and p-AlGaN Ohmic contact on p-GaN with a hole concentration of 6.5 x 10(17) cm(-3), shows the lowest rho(c) of similar to 9.2 x 10(-6) Omega cm(2), when GaN was treated in HCl: H2O (3:1) solution before metal deposition and annealed at 500 degrees C for 10 minutes in 90% N-2 and 10% O-2 atmosphere. Similar procedure applied on p-AlxGa1-xN (x = 5-7%), with a hole concentration of 2.3 x 10(17) cm(-3), yields a rho(c) of 1.8 x 10(-4) Omega cm(2). An increase is observed in rho(c). when Mg doping exceeds 4 x 10(19) cm(-3) in both p-GaN and p-AlGaN. This is attributed to Mg self compensation. This increase is more pronounced in AlGaN which we attribute to the presence of residual native aluminum oxides.