Wet etch clean-up of plasma damage for 1.68 kV breakdown in NiO/β-Ga2O3 chlorine-etched PN diodes

The effectiveness of relevant wet chemical treatments in mitigating post-dry etch plasma damage to β-Ga2O3 prior to NiO heterojunction formation was investigated using electrical and surface characterization techniques. Wet etches of warm (80 °C) H3PO4, (70 °C) tetramethylammonium hydroxide (TMAH), and room-temperature 10:1 dilute HCl were used as post-BCl3 plasma etch treatments prior to the formation of β-Ga2O3-NiO PN heterojunction diodes and β-Ga2O3 Schottky barrier diodes (SBDs). Remarkably, all etched and treated SBDs displayed low ideality factors (1.04–1.07), while the breakdown voltages (VBD) and specific on-resistances (RON,SP) varied significantly across treatments, indicating that ideality alone cannot distinguish best practices in surface preparation techniques. The most successful treatment was a TMAH (70 °C, 10%, and 2 min), resulting in PN diodes with high VBD and low RON,SP of 1680 V and 4.78 mΩ cm2, respectively. The HCl-treated sample (1550 V) performed similarly in VBD to the etched and untreated control PN diodes (1580 V), improved the breakdown performance for the SBD devices (860 V HCl, 780 V untreated), and improved RON,SP in both cases—3.75 mΩ cm2 HCl vs 4.36 mΩ cm2 untreated for SBDs and 5.10 mΩ cm2 HCl vs 5.57 mΩ cm2 untreated for PN diodes. However, the warm H3PO4 treatment (1500 V VBD, 4.57 mΩ cm2RON,SP) caused a decrease in PN breakdown performance despite exhibiting the lowest RON,SP. All treated samples were similar in RMS roughness by AFM characterization, but showed significant differences in XPS characterization, indicating that surface contamination rather than a roughened surface affected the breakdown performance of devices.