  This letter reports the first demonstration of AlN Schottky diodes on bulk
AlN substrates by metalorganic chemical vapor phase deposition (MOCVD) with
breakdown voltages exceeding 3 kV. The devices exhibited good rectifying
characteristics with ON/OFF ratios on the order of 10^6 to 10^8 and excellent
thermal stability from 298 to 623 K. The device Schottky barrier height
increased from 0.89 to 1.85 eV, and the ideality factor decreased from 4.29 to
1.95 with increasing temperatures, which was ascribed to the inhomogeneous
metal/AlN interface. At reverse bias of -3 kV, the devices showed a low leakage
current of 200 nA without the incorporation of any field plate structures or
passivation techniques. This work demonstrates the potential of AlN as an
ultra-wide bandgap semiconductor and represents a big step toward the
development of multi-kV AlN high-voltage and high-power devices.
