Correlation between Fermi-Level Hysteresis and Sulfur Vacancy-Based Traps on MoS2

Abstract

Two-dimensional (2D) transition metal dichalcogenides (TMDs) have emerged as promising candidates for memory cells and data storage devices, thanks to their exceptional electrical properties and high data storage capabilities enabled by their layered structures. Despite the significant role of charge traps induced by defects in TMD-based memory devices in contributing to hysteresis (ΔV) as a memory window, there remains a lack of research on how different energy levels of these traps specifically affect ΔV. In this study, we report the simultaneous measurement of the spatially distributed ΔV and energy-dependent trap density (D_t) in a MoS₂/hBN structure by using Kelvin probe force microscopy. We observed a strong correlation of 0.61 between the ΔV and D_t in the trap states at 0.4–0.8 eV below the conduction band (E_C), which is attributed to sulfur vacancies (SVs) in MoS₂. Additionally, a slight correlation of 0.3 between the ΔV and D_t in the trap states at approximately 0.4 eV below the E_C was observed, arising from the trap states via the hybridization of individual SVs, aligning well with previous findings. Furthermore, thiol molecule treatment on MoS₂ completely mitigates these correlations by healing the SVs. Our technique, capable of quantifying the energy levels of trap states and their impact on hysteresis, provides crucial insights into the origins of charge trap sources and their charge trapping mechanisms. These insights are essential for the development of TMD-based memory devices and data storage cells.