Oxygen-Activated Surface Chemistry Enabling Low-Temperature CVD of RuS ₂ for Broadband Photodetectors

Ruthenium sulfide (RuS 2 ) is a promising channel material for light detection because of its high carrier mobility, suitable bandgap, and long-term stability. However, conventional synthesis requires high temperatures and predominantly yields nanoparticle-based structures, which are unsuitable for optoelectronic devices. In this work, we demonstrate the direct growth of high-quality RuS 2 films at a remarkably low temperature of 300 °C, enabled by an O 2 coinjection strategy during chemical vapor deposition (CVD). Systematic characterization reveals that O 2 plays a critical role in facilitating low-temperature growth while suppressing metallic Ru or RuO 2 formation. Machine-learning interatomic potential (MLIP)-based theoretical analysis on surface reactions reveals that slightly oxidized RuS 2 surfaces formed under O 2 /H 2 S coinjection enhance H 2 S activation, surface reactivity, and precursor-ligand elimination, thereby supporting low-temperature RuS 2 CVD growth. Consequently, the O 2 -assisted process yields phase-pure, polycrystalline RuS 2 films with minimal oxygen incorporation. Metal–semiconductor–metal (MSM) RuS 2 photodetectors exhibit broadband photoresponse across the visible to near-infrared (NIR) region, very low dark current (∼1.7 nA), and high responsivity, along with fast response times (47/65 μs) and excellent stability. These findings demonstrate that O 2 -assisted CVD provides a robust, low-temperature route for synthesizing RuS 2 thin films and highlight their potential for next-generation optoelectronic applications.