Oxygen Driven Defect Engineering of Monolayer MoS2 for Tunable Electronic, Optoelectronic, and Electrochemical Devices

Abstract Molybdenum disulfide (MoS 2 ), a two‐dimensional (2D) semiconducting material harbors intrinsic defects that can be harnessed to achieve tuneable electronic, optoelectronic, and electrochemical devices. However, achieving precise control over defect formation within monolayer MoS 2 , remains a notable challenge. Here, an in‐situ defect engineering approach for monolayer MoS 2 using a pressure‐dependent chemical vapor deposition (CVD) process is presented. Monolayer MoS 2 grown in a low pressure CVD conditions (LP‐MoS 2 ) produces sulfur vacancy ( V s ) induced defect‐rich crystals primarily attributed to the oxygen‐deficient growth conditions. Conversely, atmospheric pressure CVD‐grown MoS 2 (AP‐MoS 2 ) passivates these defects with oxygen from ambient conditions. This disparity in defect profiles profoundly impacts crucial functional properties and device performance. AP‐MoS 2 shows a drastically enhanced photoluminescence, which is significantly quenched in LP‐MoS 2 attributed to in‐gap electron donor states induced by the V s defects. However, the n‐doping induced in LP‐MoS 2 generates enhanced photoresponsivity and detectivity in fabricated photodetectors compared to the AP‐MoS 2 ‐based devices. Defect‐rich LP‐MoS 2 outperforms AP‐MoS 2 as channel layers of field‐effect transistors (FETs), as well as electrocatalytic material for hydrogen evolution reaction (HER). This work presents a single‐step CVD approach for in situ defect engineering in monolayer MoS 2 and presents a pathway to control defects in other monolayer 2D materials.