Leakage current reduction by thermal oxidation in Ni/Au Schottky contacts on lattice-matched In_0.18Al_0.82N/GaN heterostructures

By using temperature-dependent current–voltage, variable-frequency capacitance–voltage, and Hall measurements, the effects of the thermal oxidation on the electrical properties of Ni/Au Schottky contacts on lattice-matched In_0.18Al_0.82N/GaN heterostructures are investigated. Decrease of the reverse leakage current down to six orders of magnitude is observed after the thermal oxidation of the In_0.18Al_0.82N/GaN heterostructures at 700 ℃. It is confirmed that the reverse leakage current is dominated by the Frenkel–Poole emission, and the main origin of the leakage current is the emission of electrons from a trap state near the metal/semiconductor interface into a continuum of electronic states associated with the conductive dislocations in the In_xAl_1-xN barrier. It is believed that the thermal oxidation results in the formation of a thin oxide layer on the In_xAl_1-xN surface, which increases the electron emission barrier height.