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Platinum Metals Rev., 2000, 44, (4), 157

High Breakdown Voltage of Au/Pt/GaN Schottky Diodes

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In power electronics (power > 1 MW), silicon carbide, gallium arsenide and gallium nitride (GaN) are being developed as alternative materials to silicon. Silicon carbide is already used in solid-state power electronic devices, such as diodes, thyristors and transistors. Wide bandgap GaN, with high breakdown voltage, is also under extensive investigation for power device uses, but little work has been reported on breakdown in GaN diode devices.

Schottky diodes can switch faster than junction diodes and are often used to measure the quality of material. Now, a team of researchers, from the National Central University, Taiwan, the University of Florida, Sandia National Laboratories, Bell Laboratories, and a consultant, U.S.A., have examined breakdown using Au/Pt/GaN Schottky diode rectifiers (G. T. Dang, A. P. Zhang, M. M. Mshewa, F. Ren, J.-I. Chyi, C-M. Lee, C. C. Chuo, G. C. Chi, J. Han, S. N. G. Chu, R. G. Wilson, X. A. Cao and S. J. Pearton, J. Vac. Sci. Technol. A, 2000,18, (4), 1135–1143).

GaN was grown by MOCVD on sapphire via NH3 and trimethylgallium precursors. The ohmic contacts were formed by Pt/Au liftoff. They were annealed before Pt/Au deposition. Optimised high-density plasma etching conditions were developed for GaN, to give minimal degradation in reverse current leakage in p-i-n mesa diodes. Reverse breakdown voltages (V rb) of up to 550 V on vertically depleting structures and > 2000 V on lateral devices were obtained. Values for the figure-of-merit (V rb)2/Ron, (Ron = on-state resistance) were 4.2 to 4.8 MW cm−2. The reverse leakage currents and forward on-voltages were slightly higher than theoretical minimum values, but comparable with reported SiC Schottky rectifiers. The GaN-devices show promise for use in ultrahigh-power switches.

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