Intrinsic defect engineering of CVD grown monolayer MoS2 for tuneable functional nanodevices
Abstract
Defects in atomically thin materials can drive new functionalities and expand applications to multifunctional systems that are monolithically integrated. An ability to control formation of defects during the synthesis process is an important capability to create practical deployment opportunities. Molybdenum disulfide (MoS2), 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 MoS2, while maintaining the structural integrity of the crystals remains a notable challenge. Here, we present a one-step, in-situ defect engineering approach for monolayer MoS2 using a pressure dependent chemical vapour deposition (CVD) process. Monolayer MoS2 grown in low-pressure CVD conditions (LP-MoS2) produces sulfur vacancy (Vs) induced defect rich crystals primarily attributed to the kinetics of the growth conditions. Conversely, atmospheric pressure CVD grown MoS2 (AP-MoS2) passivates these Vs defects with oxygen. This disparity in defect profiles profoundly impacts crucial functional properties and device performance. AP-MoS2 shows a drastically enhanced photoluminescence, which is significantly quenched in LP-MoS2 attributed to in-gap electron donor states induced by the Vs defects. However, the n-doping induced by the Vs defects in LP-MoS2 generates enhanced photoresponsivity and detectivity in our fabricated photodetectors compared to the AP-MoS2 based devices. Defect-rich LP-MoS2 outperforms AP-MoS2 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 MoS2 and presents a pathway to control defects in other monolayer material systems.
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