Realizing the anisotropic deep trenching of GaN without surface damage is essential for the fabrication of GaN-based devices. However, traditional dry etching technologies introduce irreversible damage to GaN and degrade the performance of the device. In this paper, we demonstrate a damage-free, rapid metal-assisted chemical etching (MacEtch) method and perform an anisotropic, deep trenching of a GaN array. Regular GaN microarrays are fabricated based on the proposed method, in which CuSO₄ and HF are adopted as etchants while ultraviolet light and Ni/Ag mask are applied to catalyze the etching process of GaN, reaching an etching rate of 100 nm/min. We comprehensively explore the etching mechanism by adopting three different patterns, comparing a Ni/Ag mask with a SiN mask, and adjusting the etchant proportion. Under the catalytic role of Ni/Ag, the GaN etching rate nearby the metal mask is much faster than that of other parts, which contributes to the formation of deep trenches. Furthermore, an optimized etchant is studied to restrain the disorder accumulation of excessive Cu particles and guarantee a continuous etching result. Notably, our work presents a novel low-cost MacEtch method to achieve GaN deep etching at room temperature, which may promote the evolution of GaN-based device fabrication.

The 10 nm p-NiO thin film is prepared by thermal oxidation of Ni on β-Ga₂O₃ to form NiO/β-Ga₂O₃ p–n heterojunction diodes (HJDs). The NiO/β-Ga₂O₃ HJDs exhibit excellent electrostatic properties, with a high breakdown voltage of 465 V, a specific on-resistance (R _on,sp) of 3.39 mΩ⋅cm², and a turn-on voltage (V _on) of 1.85 V, yielding a static Baliga's figure of merit (FOM) of 256 MW/cm². Also, the HJDs have a low turn-on voltage, which reduces conduction loss dramatically, and a rectification ratio of up to 10⁸. Meanwhile, the HJDs' reverse leakage current is essentially unaffected at temperatures below 170 °C, and their leakage level may be controlled below 10⁻¹⁰ A. This indicates that p-NiO/β-Ga₂O₃ HJDs with good thermal stability and high-temperature operating ability can be a good option for high-performance β-Ga₂O₃ power devices.

A Cu-assisted photoelectron-chemical etching is proposed to fabricate GaN nanowires. The functional mechanism of assisted metals, etchant concentrations, and the addition of H₂O₂ has been investigated based on theoretical analysis and experiments.