High Breakdown Voltage GaN Schottky Diodes for THz Frequency Multipliers

Quasi-vertical gallium nitride (GaN) Schottky diodes on silicon carbide (SiC) substrates were fabricated for frequency multiplier applications. The epitaxial structure employed had an n(-) layer of 590 nm with doping 6.6 x 10(16) cm(-3), while the n(+) layer was 950 nm thick, with doping 2 x 10(19) cm(-3). Potassium hydroxide (KOH) chemical surface treatment before Schottky contact metallization was employed to study its effect in improving the diode parameters. The KOH-treated diode demonstrated a breakdown voltage of - 27.5 V, which is the highest reported for this type of diode. Cut-off frequencies around 500 GHz were obtained at high reverse bias (- 25 V) in spite of high series resistance. The result obtained in breakdown voltage value warrants further research in surface treatment and post-annealing of the Schottky contact optimization in order to decrease the series resistance.