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This work demonstrates an in situ etching technique for β-Ga2O3 using solid-source metallic gallium (Ga) in a low-pressure chemical vapor deposition (LPCVD) system, enabling clean, anisotropic, plasma damage-free etching. Etching behavior was systematically studied on (2¯01) β-Ga2O3 films and patterned (010) β-Ga2O3 substrates as a function of temperature (1000–1100 °C), Ar carrier gas flow (80–400 sccm) and Ga source-to-substrate distance (1–5 cm). The process exhibits vapor transport- and surface-reaction-limited behavior, with etch rates reaching a maximum of ∼2.25 µm/h on (010) substrates at 1050 °C and 2 cm spacing. Etch rates decrease sharply with increasing source-to-substrate distance due to reduced Ga vapor availability, while elevated temperatures enhance surface reaction kinetics through increased Ga reactivity and suboxide formation, leading to enhanced etch rates. In-plane anisotropy studies using radial trench patterns reveal that the (100) orientation produces the most stable etch front, characterized by smooth, vertical sidewalls and minimal lateral etching, consistent with its lowest surface free energy. In contrast, orientations such as (101), which possess higher surface energy, exhibit pronounced lateral etching and micro-faceting. As the trench orientation progressively deviates from (100), lateral etching increases. Facet evolution is observed between (100) and (1¯02), where stepped sidewalls composed of alternating (100) and (1¯02) segments progressively transition into a single inclined facet, which stabilizes along (100) or (1¯02) depending on the trench orientation. The (100)-aligned fins exhibit minimal bottom curvature, while (201)-aligned structures display increased under-etching and trench rounding. Collectively, these findings establish LPCVD-based in situ etching as a scalable, damage-free, and orientation-selective technique for fabricating high-aspect-ratio β-Ga2O3 3D structures in next-generation power devices. 

In the rapidly evolving field of quantum computing, niobium nitride (NbN) superconductors have emerged as integral components due to their unique structural properties, including a high superconducting transition temperature (Tc), exceptional electrical conductivity, and compatibility with advanced device architectures. This study investigates the impact of high-temperature annealing and high-dose gamma irradiation on the structural, electrical, and superconducting properties of NbN films grown on GaN via reactive DC magnetron sputtering. The as-deposited cubic δ-NbN (111) films exhibited a high intensity distinct x-ray diffraction (XRD) peak, a high Tc of 12.82 K, and an atomically flat surface. Annealing at 500 and 950 °C for varying durations revealed notable structural and surface changes. High-resolution scanning transmission electron microscopy (STEM) indicated improved local ordering, while atomic force microscopy showed reduced surface roughness after annealing. X-ray photoelectron spectroscopy revealed a gradual increase in the Nb/N ratio with higher annealing temperatures and durations. High-resolution XRD and STEM analyses showed lattice constant modifications in δ-NbN films, attributed to residual stress changes following annealing. Additionally, XRD φ-scans revealed a sixfold symmetry in the NbN films due to rotational domains relative to GaN. While Tc remained stable after annealing at 500 °C, increasing the annealing temperature to 950 °C degraded Tc to 8.7 K and reduced the residual resistivity ratio from 0.85 in the as-deposited films to 0.29 after 30 min annealing. The effects of high-dose gamma radiation [5 Mrad (Si)] were also studied, demonstrating minimal changes to crystallinity and superconducting performance, indicating excellent radiation resilience. These findings highlight the potential of NbN superconductors for integration into advanced quantum devices and its suitability for applications in radiation-intensive environments such as space, satellites, and nuclear power plants.