Novel type of ohmic contacts to p-doped GaN using polarization fields in thin In_xGa_1-xN capping layers

Thin p-doped InGaN layers on p-doped GaN were successfully used to demonstrate a new type of low-resistance ohmic contact. A significant reduction of specific contact resistance can be achieved by increasing the free-hole concentration and the probability for hole tunneling through the Schottky barrier as a consequence of polarization-induced band bending. As obtained from the transmission-line method, the specific contact resistances of Ni (10 nm)/Au (30 nm) contacts deposited on InGaN capping layers were 1.2 × 10^-2 Ωcm² and 6 × 10^-3 Ωcm² for capping layer thicknesses of 20 nm and 2 nm, respectively.