Monolayer WS₂ Nanosheets Passivated with\nHfO₂ for Enhanced Photodetectors

Abstract

Two-dimensional\ntransition metal dichalcogenides (TMDCs) are widely\nused in electronic and optoelectronic devices. However, the conventional\nchemical vapor deposition (CVD) method is difficult to synthesize\nlarge-area monolayer WS₂ nanosheets stably, which limits\nthe application of WS₂ in the field of photoelectric detection.\nIn this work, we propose an innovative NaCl-assisted CVD method that\nallows freely adjustable substrate positions for synthesizing monolayer\nWS₂ nanosheets. The obtained maximum grain size of the\nmonolayer WS₂ nanosheets is up to 30 μm. Subsequently,\nwe investigated the effect of the HfO₂ passivation layer\non the performance of the metal–semiconductor–metal\n(MSM) WS₂-based photodetectors. The HfO₂ passivation\nlayer brought an overall improvement to the performance of the fabricated\nphotodetectors, exhibiting a high responsivity of 1093.1 AW^–1, a high specific detectivity of 2.6 × 10¹² Jones,\nand a high external quantum efficiency of 2.1 × 10⁵%. Furthermore, the physical mechanism of the fabricated photodetectors\nhas been discussed to explain how the HfO₂ passivation\nlayer takes effect in the improvement of the WS₂-based\nphotodetectors. This result can accelerate the development of optoelectronic\ndevices based on TMDCs.