Low-resistance Ni/Al Ohmic contacts applied to a nonpolar a-plane n-type GaN

The authors report upon a low-resistance Ni/Al Ohmic contact to a nonpolar n-type a-plane GaN with respect to the annealing temperature. The Schottky behavior of the Ni/Al contact changes to a linear Ohmic behavior at a 700 °C annealing, at which the specific contact resistivity of the Ni/Al contact became as low as 5.8×10−5 whereas that of a typical Ti/Al contact was 1.6×10−3 Ω cm2. This improvement is attributed to a lowering of the Schottky barrier height via a Ni–Al interdiffused layer, formed at the interface between the metal and the nonpolar a-plane n-type GaN during the annealing process.