Dielectric Properties and Ion Transport in Layered MoS₂ Grown by Vapor-Phase Sulfurization for Potential Applications in Nanoelectronics

Abstract

Electronic and dielectric properties of vapor-phase grown MoS2 have been investigated in metal/MoS2/silicon capacitor structures by capacitance–voltage and conductance-voltage techniques. Analytical methods confirm the MoS2 layered structure, the presence of interfacial silicon oxide (SiOx) and the composition of the films. Electrical characteristics in combination with theoretical considerations quantify the concentration of electron states at the interface between Si and a 2.5–3 nm thick silicon oxide interlayer between Si and MoS2. Measurements under electric field stress indicate the existence of mobile ions in MoS2 that interact with interface states. On the basis of time-of-flight secondary ion mass spectrometry, we propose OH– ions as probable candidates responsible for the observations. The dielectric constant of the vapor-phase grown MoS2 extracted from CV measurements at 100 kHz is 2.6 to 2.9. The present study advances the understanding of defects and interface states in MoS2. It also indicates opportunities for ion-based plasticity in 2D material devices for neuromorphic computing applications.

Nonvolatile Resistive Switching in Nanocrystalline Molybdenum Disulfide with Ion‐Based Plasticity

“…Endurance and state‐retention tests performed on the devices demonstrate that the observed non‐volatile RS behavior is quite stable over a period despite successive biasing. Comparison of measurements carried out in ambient and vacuum conditions provide plausible arguments that the observed RS effect is due to OH − ions that stem from catalytic splitting of adsorbed water molecules, in agreement with previous findings 36. Analytical simulations support experiments and suggest that the movement of such ions toward (away from) the Si/MoS 2 interface in response to negative (positive) electric‐fields dictates the observed RS behavior by tuning the energy barriers at the interface.…”

“…In the present devices, the observed RS effect can be explained by movement of OH − ions inside the layered MoS 2 . The presence of OH − ions in MoS 2 have been experimentally observed in a previous study through time‐of‐flight secondary ion mass spectroscopy and electrical characterizations 36. There, it was also demonstrated that the OH − ions move presumably along the van der Waals gaps toward (away from) the Si/MoS 2 interface in response to a negative (positive) bias applied on the top electrode 36,37.…”

“…Recently, we demonstrated the presence of hydroxyl (OH − ) ions and their field‐induced movement in vapor‐phase grown MoS 2 with vertically aligned layers 36,37. Here, we demonstrate the existence and investigate the origin of nonvolatile resistive switching in silicon (Si)/MoS 2 /metal heterostructure devices, where MoS 2 with vertically aligned layers serves as the RS medium.…”

“…Details of the MoS 2 synthesis process are described in Supporting Information and in ref. 36. After MoS 2 growth, top electrodes were defined on the MoS 2 films by employing a photolithography step followed by evaporation of a stack of 20 nm Cr and 120 nm gold (Au) and a lift‐off process.…”

Recommended Methods to Study Resistive Switching Devices

“…[102] It should be also noted that one method to avoid the formation of wrinkles in 2D materials is to enhance the roughness of the substrate where it is transferred. [105] In ref. [105] In ref.…”