Impacts of localized charge accumulation on photocurrent dynamics in metal-MoS₂ contacts

Monolayer molybdenum disulfide (1L-MoS₂) has attracted a lot of attention due to its excellent electrical and optoelectronic properties. However, the instability of the metal-semiconductor junction remains a challenge, which greatly affects the performance of the drain/source contacts. Despite the promising potential offered by 1L-MoS₂ as an ultrathin two-dimensional semiconductor, its optoelectronic performance is often compromised by contact issues at the metal-semiconductor junctions. In particular, localized charge accumulation (LCA) can cause barrier height fluctuation, which affects carrier transport and activated trap states. In this study, we use photocurrent mapping to investigate photocurrent reduction and its optoelectronic properties depending on the device position. The results show a significant reduction in the photoresponsivity and photodetectivity of the LCA region compared to the channel. Moreover, the decay time of the LCA region was approximately twice as long as that of the channel, indicating the presence of deep traps leading to slow switching. This study shows that the photogenerated LCA region significantly impairs optoelectronics performance by disturing carrier transport, exhiniting up to a 30-fold reduction in photocurrent compared to the channel. It also provides a critical understanding necessary for engineering next-generation optoelectronics based on 2D semiconductors.