Ohmic contacts to p-type GaN mediated by polarization fields in thin In_xGa_1-xN capping layers

Low-resistance ohmic contacts are demonstrated using thin p-type InGaN layers on p-type GaN. It is shown that the tunneling barrier width is drastically reduced by polarization-induced electric fields in the strained InGaN capping layers resulting in an increase of the hole tunneling probability through the barrier and a significant decrease of the specific contact resistance. The specific contact resistance of Ni (10 nm)/Au (30 nm) contacts deposited on the InGaN capping layers was determined by the transmission line method. Specific contact resistances of 1.2×10^-2cm² and 6×10^-3cm² were obtained for capping layer thicknesses of 20 nm and 2 nm, respectively.