Vertical Schottky diodes were fabricated on the bulk GaN substrate with decreasing impurity concentration from N-face to Ga-face. An array of circular Pt Schottky contacts and a full backside Ti/Al/Ni/Au ohmic contact were prepared on the Ga-face and the N-face of the n-GaN substrate, respectively. The Schottky diode exhibits a minimum specific on-state resistance of 1.3 m Omega cm(2) and a maximum breakdown voltage of 600 V, resulting in a figure-of-merit of 275 MW cm(-2). An ultra-low reverse leakage current density of 3.7 x 10(-4) A cm(-2) at reverse bias of 400 V was observed. Temperature-dependent I-V measurements were also carried out to study the forward and reverse transportation mechanisms.
