Crack-free thick α-Ga2O3 films grown on Ni–Pd-CNT nanoalloy masks

We report a Ni–Pd–CNT-based nanoalloy mask that improves the crystalline quality of α-Ga₂O₃ epilayers grown via halide vapor phase epitaxy (HVPE). Conventional heteroepitaxy of α-Ga₂O₃ on sapphire substrates typically results in high dislocation densities due to lattice and thermal expansion mismatches. To address this problem, a Ni–Pd–CNT nanoalloy layer was deposited on a (0001)-oriented α-Ga₂O₃ buffer layer using electroless plating and spray coating, and α-Ga₂O₃ was regrown for 15 min. Among the plating durations tested (20, 40, and 60 s), the 40 s condition yielded the thickest epilayer (∼11 μm), the lowest etch pit density (∼4.8 × 10⁷ cm⁻²), and the narrowest X-ray diffraction rocking curve for the asymmetric (10–14) reflection.

AFM and SEM analyses confirmed improved surface uniformity and reduced tilting of seed crystals under these conditions. All samples exhibited high optical transmittance (>80 %) in the visible region and a direct bandgap of ∼5.13 eV, which indicates that the optical properties remained stable regardless of the Ni content. These results show that the Ni–Pd–CNT-assisted nano-epitaxial lateral overgrowth (nano-ELOG) approach effectively reduces threading dislocation density while preserving wide bandgap transparency. This method offers a low-cost, scalable route for producing high-quality α-Ga₂O₃, with strong potential for next-generation power electronics and UV optoelectronic devices.