Comparative analysis of Schottky barriers for heterogeneous defect domains in monolayer WS2 field-effect transistors

Abstract

A major bottleneck in the applications of two-dimensional transition metal dichalcogenides (TMDs) is the realization of ohmic contacts by overcoming the Schottky barrier (SB) at metal–semiconductor interfaces. Although the physical properties of point defects in TMDs are the key to determining the SB characteristics, the correlation between the defect types and SBs is yet to be systematically explored. Here, we investigated the SB characteristics depending on the S vacancy (SV) and W vacancy (WV) in hexagonal WS2 field-effect transistors (FETs). This was implemented by fabricating the SV and WV FETs in each domain on a single-flake monolayer. Compared to WV FET, the SV FET exhibited a 10 times higher doping concentration and 4 times higher Coulomb scattering coefficient (α) resulting in higher low-frequency noise. The comparative SB characteristics of both FETs were investigated by Arrhenius plot for the on-current at high temperatures. Below 360 K, the activation energies (Ea) of the SV and WV FETs exhibited different values of 0.071 and 0.115 eV, respectively, whereas those values are similar above 360 K because sufficient thermal energy allows for tunneling at SBs. These results help us understand the correlation between the defect type, doping level, and SB in TMD-based electronic devices.