Ultra‐Sensitive β‐Ga₂O₃ Solar‐Blind Photodetector with High‐Density Al@Al₂O₃ Core−Shell Nanoplasmonic Array

Abstract β‐Ga₂O₃ solar‐blind photodetectors (PDs) are attracting great attention for broad applications. However, their detection sensitivities are still lower than expected after tremendous efforts. The phenomenon of localized surface plasmon resonance (LSPR) offers another approach beyond conventional techniques to engineer the photodetection performance, but extending the plasmonic properties into the deep‐ultraviolet region faces severe challenges, among which strictly controlling the nanostructures structural properties is extremely prominent besides material selection. Herein, well‐defined Al@Al₂O₃ core−shell nanostructure arrays are fabricated with sub‐50 nm feature sizes, narrow dimension distributions, periodic graphene‐like patterns, and extremely high densities (up to 152.7 counts µm⁻²). The decorated β‐Ga₂O₃ PDs exhibit significantly enhanced sensitivities without response spectra broadening. Particularly, the sample with a 42‐nm nanostructure array possesses an ultrahigh specific detectivity (4.22 × 10¹⁵ Jones), being one of the top among film‐type gallium oxide PDs, and an excellent responsivity of 216.0 A W⁻¹ peaked at 235 nm. Moreover, the passivation effect of self‐terminating native oxide shell is confirmed. The finite‐difference time‐domain simulations based on isolated, dimer, and arrayed models not only demonstrate the presence of LSPR, but also reveal the critical contribution of nanostructure density. The findings provide an alternative platform to break the bottleneck and develop ultra‐sensitive, truly solar‐blind PDs for advanced optoelectronic systems.