Vapor‐Phase Synthesis of Ultrathin Indium Nitrides via Self‐Assembled Oxide Intermediates for Ultraviolet Photodetection

Indium nitride (InN) has garnered significant attention for high‐speed semiconductor devices. However, its inherently nonlayered crystal structure poses a significant challenge for the integration into emerging 2D material systems. Here, the article reports the synthesis of ultrathin polycrystalline InN film and its potential applications in light sensing. The synthesis involves the ammonolysis of indium oxide layers that were squeeze‐printed from liquid indium. The intermediate bromination facilitates the transformation into crystalline InN nanosheets characterized by a thickness of ≈47 nm and an optical bandgap around 1.35 eV. The photodetectors designed on ultrathin InN films exhibit a responsivity ( R _λ ) of 2.11 A·W ⁻¹ , an external quantum efficiency ( EQE ) of 4.39 × 10 ² %, and a detectivity ( D* ) of 6.5 × 10 ¹¹ Jones under 365 nm (≈1.0 mW cm ⁻² , bias = 1 V), comparable to that of other InN materials prepared by MBE, MOCVD, or RF sputtering. In addition, the image reproduction capability of ultrathin InN photodetectors is showcased on a single‐pixel imaging platform (excited by a 360 nm laser, 1 V), highlighting the potential for high‐precision optical imaging applications. This cost‐effective method using liquid metal for the synthesis of ultrathin/polycrystalline InN films offers a promising strategy for integrating industrially important III nitride semiconductors into the future atomically thin systems.