No abstract

The GaN Schottky diodes capable of operating in the 300-700-V range with low turn-on voltage (0.7 V) and forward conduction currents of at least 10 A at 1.4 V (with corresponding forward current density of 500 A/cm 2 ) are attractive for applications ranging from power distribution in electric/hybrid electric vehicles to power management in spacecraft and geothermal, deep-well drilling telemetry.A key requirement is the need for edge-termination design to prevent premature breakdown because of field crowding at the edge of the depletion region. We describe the simulation of structures incorporating various kinds of edge termination, including dielectric overlap and ion-implanted guard rings. Dielectric overlap using 5-µm termination of 0.1-0.2-µm-thick SiO 2 increases the breakdown voltage of quasi-vertical diodes with 3-µm GaN epi thickness by a factor of ϳ2.7. The use of even one p-type guard ring produces about the same benefit as the optimized dielectric overlap termination.

The performance of Schottky rectifiers fabricated with dielectric overlap edge termination on epitaxial layers grown on a free-standing GaN template is reported. The power figure-of-merit (VB)2/RON where VB is the reverse breakdown voltage and RON is the on-state resistance was 11.5 MW cm−2. The forward turn-on voltage was ∼3.5 V at 25 °C, with an on-state resistance of ∼5×10−3 Ω cm2. The reverse recovery time was ⩽50 ns in switching from forward bias to reverse bias. The reverse breakdown showed a temperature coefficient of −0.45 V/C.

Zinc oxide is generally considered to be radiation hard, although there are few experimental reports supporting this assertion. In this paper, we present results on the changes in electrical performance of bulk Pt/ZnO Schottky rectifiers exposed to 40-MeV protons at fluences from 5 ϫ 10 9 cm Ϫ2 to 5 ϫ 10 10 cm Ϫ2 . These doses correspond to more than 10 years or 100 years, respectively, in low-earth satellite orbit. The reverse breakdown voltage of the ZnO diodes increased from ϳ3.6 V in unirradiated devices to ϳ4 V after the highest proton dose. The effective barrier height decreased with proton dose, while the diode ideality factor increased from 1.8 to 1.9 for the highest dose. These devices appear promising for both aerospace and terrestrial applications where irradiation hardness is a prerequisite. The main degradation mechanism appears to be creation of recombination centers and traps.

Bulk ZnO Schottky rectifiers with Pt rectifying contacts were exposed to 40 MeV protons at fluences from 5 × 109 to 5 × 1010 cm–2. These doses correspond to that received in more than 10 or 100 years, respectively, in low earth satellite orbit. The reverse breakdown voltage of the ZnO diodes increased from ∼3.2 V (taken at a current density of 0.1 A/cm2) in unirradiated devices to ∼3.9 V after the highest proton dose. The effective barrier height decreased with proton dose from 0.37 eV to 0.35 eV while the diode ideality factor increased from 1.8 to 1.9 for the 5 × 1010 dose. The very high tolerance of the ZnO diodes to high doses of energetic protons suggests that this material is well‐suited to applications requiring high radiation tolerance. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)