Monolayer WS₂ Nanosheets Passivated with HfO₂ for Enhanced Photodetectors

Two-dimensional transition metal dichalcogenides (TMDCs) are widely used in electronic and optoelectronic devices. However, the conventional chemical vapor deposition (CVD) method is difficult to synthesize large-area monolayer WS 2 nanosheets stably, which limits the application of WS 2 in the field of photoelectric detection. In this work, we propose an innovative NaCl-assisted CVD method that allows freely adjustable substrate positions for synthesizing monolayer WS 2 nanosheets. The obtained maximum grain size of the monolayer WS 2 nanosheets is up to 30 μm. Subsequently, we investigated the effect of the HfO 2 passivation layer on the performance of the metal–semiconductor–metal (MSM) WS 2 -based photodetectors. The HfO 2 passivation layer brought an overall improvement to the performance of the fabricated photodetectors, exhibiting a high responsivity of 1093.1 AW –1, a high specific detectivity of 2.6 × 10 12 Jones, and a high external quantum efficiency of 2.1 × 10 5 %. Furthermore, the physical mechanism of the fabricated photodetectors has been discussed to explain how the HfO 2 passivation layer takes effect in the improvement of the WS 2 -based photodetectors. This result can accelerate the development of optoelectronic devices based on TMDCs.