This work demonstrates a self-aligned implanted mesa termination for GaN-on-GaN vertical Schottky barrier diodes (SBDs), and studies its effects on electrical characteristics and breakdown behaviors of diodes. A self-aligned mesa termination with nitrogen implantation (SNT) has been proposed and fabricated to alleviate electric field crowding and suppress the sidewall leakage current near the edge of Schottky junction, as explained by technology computer-aided design (TCAD) simulations and validated through emission microscopy images. The SBD with SNT (SNT-SBD) exhibits an enhanced breakdown voltage (BV) from 224 to 615 V, achieving a critical electric field of 2.19 MV/cm and a high Baliga Figure of Merit 1.64 GW/cm2. Meanwhile, as predicted by the simulation-optimized structure, it is observed that the destructive breakdown ideally occurs in the non-edge active region of the Schottky junction, not at the common edge region. The as-fabricated SNT-SBD maintains a low normalized dynamic on-resistance below 1.03 under a high reverse bias of 550 V (∼90% BV) and exhibits negligible forward performance degradation under a pulsed off-state stress test, indicating minimized defect densities in GaN materials and the effectiveness of the optimized fabrication processes. This efficient termination technology potentially holds promise as a building block for high-voltage vertical power devices and offers a valuable process solution for investigating the electrical characteristics of wide-bandgap materials under high-voltage conditions.

In this work, we present a low-damage p-GaN surface processed by atomic layer etching (ALE), enabling high-performance Ohmic contacts. The mechanism underlying surface modifications introduced by various etching processes were studied in detail. Compared to conventional dry etch, ALE preserves the pristine surface stoichiometry comparable to as-grown p-GaN, effectively suppressing the formation of detrimental surface defects. Crucially, this atomic-level controlled process minimizes the increase in downward band bending and maintains the intrinsic surface electrical properties. Thus, metal contacts fabricated on the ALE-processed p-GaN exhibit an excellent Ohmic behavior. Collectively, these results not only establish low-surface-degradation contacts, but also provide a fundamental understanding required for advancing GaN-based device physics and designs.

The dynamic interactions among multiple trap states in the carbon-doped (C-doped) GaN buffer of AlGaN/GaN high-electron-mobility transistors have been studied and quantitatively characterized through a time-resolved optoelectronic spectroscopy approach. This technique combines transient channel current analysis, back-gate bias stress, and tunable sub-bandgap illumination to elucidate the underlying ionization and recombination mechanisms, which govern trap behaviors under combined electrical and optical excitation. According to the back-gating measurements, the ionization of C-related acceptor traps in the buffer layer can be confirmed as the dominant mechanism. Compared with dark conditions, red illumination accelerated current delay, indicating enhanced ionization of acceptor traps under the combined influence of electric and optical fields. Conversely, the current increase observed under blue and green illumination confirmed the presence of donor traps. Notably, the activation of donor traps under blue illumination, which are classified as CN (0/+) traps, was further confirmed by cathodoluminescence spectroscopy. The proposed method is able to effectively reveal both acceptor and donor traps in the GaN layer, which cannot be achieved by conventional approaches.