Ohmic contacts to p-type GaN mediated by polarization fields in thin InxGa1-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 1.2x10(-2) Omega cm(2) and 6x10(-3) Omega cm(2) were obtained for capping layer thicknesses of 20 nm and 2 nm, respectively. (C) 2002 American Institute of Physics.