Analysis of Schottky barrier heights and reduced Fermi-level pinning in monolayer CVD-grown MoS₂ field-effect-transistors

Abstract

Chemical vapor deposition (CVD)-grown monolayer (ML) molybdenum disulfide (MoS2) is a promising material for next-generation integrated electronic systems due to its capability of high-throughput synthesis and compatibility with wafer-scale fabrication. Several studies have described the importance of Schottky barriers in analyzing the transport properties and electrical characteristics of MoS2 field-effect-transistors (FETs) with metal contacts. However, the analysis is typically limited to single devices constructed from exfoliated flakes and should be verified for large-area fabrication methods. In this paper, CVD-grown ML MoS2 was utilized to fabricate large-area (1 cm x 1 cm) FET arrays. Two different types of metal contacts (i.e., Cr/Au and Ti/Au) were used to analyze the temperature-dependent electrical characteristics of ML MoS2 FETs and their corresponding Schottky barrier characteristics. Statistical analysis provides new insight about the properties of metal contacts on CVD-grown MoS2 compared to exfoliated samples. Reduced Schottky barrier heights (SBH) are obtained compared to exfoliated flakes, attributed to a defect-induced enhancement in metallization of CVD-grown samples. Moreover, the dependence of SBH on metal work function indicates a reduction in Fermi level pinning (FLP) compared to exfoliated flakes, moving towards the Schottky-Mott limit. Optical characterization reveals higher defect concentrations in CVD-grown samples supporting a defect-induced metallization enhancement effect consistent with the electrical SBH experiments.

Improvements in 2D p-type WSe2 transistors towards ultimate CMOS scaling

“…We can select metal contacts with WF that result in good band alignment (i.e., a small SBH) and ideally a seamless injection of charge carriers into the channel. However, non-ideal effects may be at play, such as Fermi-level “pinning”, affecting our ability to correctly adjust the SBH 33 , 34 . Therefore, it is essential to extract the SBH to identify the contribution of Schottky junctions on contact resistivity.…”

Hexagonal boron nitride (h-BN) memristor arrays for analog-based machine learning hardware

“…Their atomic scale thicknesses and pristine (i.e., dangling-bond free) surfaces could enable ultra-dense integration for next-generation integrated electronic systems 5 . Consequently, many studies have evolved from the demonstration of isolated devices (e.g., field effect transistors or FETs) based on exfoliated flakes towards large-area methods for fabrication of integrated circuits with 2D materials [6][7][8][9][10][11][12] . While early device demonstrations focused predominantly on FET applications [13][14][15][16] , recent studies have proposed memory and neuromorphic devices based on the non-volatile resistive-switching (NVRS) behavior observed in various 2D materials including transition metal dichalcogenides (TMDC) 17 , black-phosphorus 18,19 , graphene 20,21 , hexagonal boron nitride (h-BN) [22][23][24][25][26][27][28][29][30] , etc.…”

Investigation on Contact Properties of 2D van der Waals Semimetallic 1T-TiS2/MoS2 Heterojunctions

“…Furthermore, based on the Arrhenius plots (Figure d) and Richardson’s eq (eq ), the effective SBH was estimated (Figure e). I D = A * T 1.5 exp ( prefix− q Φ B k B T ) [ prefix− 1 + exp ( prefix− q V DS k B T ) ] where V ds is equal to 1 V, A * is the Richardson constant, k B is the Boltzmann constant, T is the temperature (Kelvin), and q Φ B is the SBH, derived from the slope of the ln( I D / T 1.5 ) versus 1/ k B T plot. The extracted SBH at the TiS 2 /ML MoS 2 heterojunction was 8.54 meV at a V ds of 1 V. This extracted SBH appears to be small compared with the previously reported SBH of MoS 2 (typically ranging from a few tens to hundreds of meV). − It could exhibit the ohmic contact properties of the TiS 2 /ML MoS 2 heterojunction. Combined with the former observations, a sufficiently small value of SBH could be one of the evidence for improving contact properties (e.g., R c ) of TiS 2 /ML MoS 2 fabricated via our process.…”