Low-resistance Ni-based Schottky diodes on freestanding n-GaN

Abstract

Schottky diodes formed on a low doped (5×1016cm−3) n-type GaN epilayer grown on a n+ freestanding GaN substrate were studied. The temperature dependent electrical characteristics of Ni contacts on the as-grown material are compared with an aqueous, potassium hydroxide (KOH) treated surface. In both cases the diodes are dominated by thermionic emission in forward bias, with low idealities (1.04 at room temperature) which decrease with increasing temperature, reaching 1.03 at 413K. The Schottky barrier height is 0.79±0.05eV for the as-grown surface compared with 0.85±0.05eV for the KOH treated surface at room temperature. This is consistent with an inhomogeneous barrier distribution. The specific on-state resistance of the diodes is 0.57mΩcm2 The KOH treatment reduces the room temperature reverse leakage current density at −30Vto1×10−5Acm−2 compared to 6×10−2Acm−2 for the as-grown samples.