Effects of oxygen plasma and hydrochloric acid surface preparation on contact formation for pseudo-vertical GaN-on-Si Schottky diodes grown by localized epitaxy

The influence of surface preparation on the metal–semiconductor interface of pseudo-vertical GaN-on-Si Schottky diodes fabricated by selective-area growth on 200 mm silicon wafers is investigated. Devices were subjected to four surface conditions prior to anode metallization: no treatment, O2 plasma, HCl etching, and O2 plasma followed by HCl treatment. Electrical measurements show that HCl treatment yields the most favorable Schottky behavior, with a higher turn-on voltage (1.0 V) and a lower ideality factor (n ≈ 1), while O2 plasma degrades device performance (VTH = 0.2 and n ≈ 1.9). The combined treatment results in the poorest Schottky characteristics despite a thinner oxide layer than with plasma alone (VTH = 0.1 and n ≈ 2.2). X-ray photoelectron spectroscopy performed before and after Ni deposition reveals that these trends correlate with changes in interfacial oxide chemistry, including effective removal of GaOx by HCl, enhanced oxidation following O2 plasma exposure, and increased disorder in the top layers due to the plasma energy. When applied prior to cathode deposition, the combined treatment of O2 plasma and HCl increases forward current density by a factor of 6 without affecting the forward-bias characteristics, underscoring the interface-specific role of surface preparation. These results highlight the need for tailored surface treatments to optimize the performance of both contacts in GaN Schottky diodes.