Electrical and Structural Evolution of Few- to Multi-Layer MoS₂ Devices Upon Electrochemical Intercalation

We systematically investigate the impact of electrochemical intercalation on the electrical and structural properties of few- to multi-layer MoS₂ field-effect transistors (FETs). Devices of varying channel thickness were subjected to KOH-based intercalation conditions, and their transport characteristics were evaluated in three stages: original, right after intercalation, and after post-annealing. We observed that MoS₂ FETs generally show reduced source-drain current and stronger hysteresis in the gate transfer curve upon the intercalation of K⁺ ions, indicating the disorder effect from intercalated K⁺ ions. However, a subsequent annealing treatment improves the device performance (enhanced source-drain current and field-effect mobility) accompanied by a negative threshold-voltage shift, presumably due to the thermal activation and redistribution of intercalated ions. These intercalation effects were examined in samples with different thicknesses and corroborated by Raman spectroscopy to elucidate the structural evolution of layered MoS₂ upon electrochemical intercalation. Together, these findings establish a comprehensive understanding of thickness-coupled electrochemical intercalation and annealing-optimization of intercalated MoS₂ FETs, offering practical design insights for stable and tunable electrochemically-engineered two-dimensional electronics.