Pseudo-vertical GaN-on-Sapphire PiN Diode: Process Optimizations and Electrical Properties

In this study, pseudo-vertical GaN-on-Sapphire PiN diodes with different mesa radii were designed, fabricated and characterized. First, critical process stages, such as mesa etching, ohmic contacts on GaN and passivation, are presented and reviewed to obtain functional diodes. Ion beam etching, with an optimized USG hard mask, seems the best solution to achieve reliable devices. Our results also show the impact of different passivation solutions on Au/Ni ohmic contact. Finally, the diodes with varying radii of the mesa (20, 40 and 60 μm) exhibit turn-on voltages of approximately 3.5 V and achieve a specific onresistance of 0.56-1.7 mΩ·cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>. More, the devices show low capacitance versus frequency properties up to 40GHz. Further adjustments on designs and fabrication processes are requested to enhance performance.