Charge Trap Dynamics in Nanobubbles on MoS₂ Nanosheets: Implications for Reliability in 2D Electronic Devices

The performance of MoS2 transistors is significantly influenced by charge trapping in pre-existing traps with a wide range of time constants. In this study, we investigate local charge trapping dynamics in nanoscale bubbles on MoS2 by comparing the frequency-dependent Fermi-level hysteresis (ΔV) in gate sweep measurements between bubble and flat regions using Kelvin probe force microscopy. We find that ΔV increases as the gate sweep frequency (f) decreases in both regions. However, it remains consistently larger in the bubble regions across all frequencies. The stronger f-dependence of ΔV in bubbles compared to flat regions is attributed to slow traps caused by water molecules confined within the bubbles. Humidity-controlled measurements reveal that in flat regions, adsorbed water molecules also enhance ΔV at lower frequencies, confirming the role of water as a dominant trapping source. To rule out other extrinsic trap sources, we repeat the measurements using an hBN insulating layer and observe similar behavior. These results demonstrate that water molecules in nanoscale bubbles act as slow charge traps and are a major contributor to hysteresis and instability, offering insights for improving the reliability of 2D electronic devices.