Аннотация:The unique properties of graphene have increased interest in two-dimensional (2D) semiconducting materials. In the past few years, transition metal dichalcogenides (TMD) are of great interest because they possess a direct band gap in the visible spectral range and allow fabrication 2D efficient electronic and optoelectronic devices [1]. Field-effect transistor (FET) is a key unit of any electronic device, and carrier mobility is an essential FET characteristic. The highest mobility value for the individual-flake TMD FET reaches 60 cm2/V*s [2]. However, all previous studies were conducted on individual flakes of TMD, i.e., nanometer crystals formed of a few TMD monolayers, and this approach is hardly compatible with the affordable technology of mass production of electronic devices.
In this work, we prepared thin films from TMD flakes of MoS2 and WS2 by a liquid-phase method and studied their electrical properties in FET. Figure 1a shows the AFM image of WS2 film, which films appears to be rather uniform though not so smooth. Raman spectroscopy data show that the TMD films are in the semiconducting phase and do not contain Mo/W oxides. We fabricated FET on SiO2/Si wafer in bottom gate bottom contacts configuration. Figure 1b shows rather weak field-effect along with off current in acquired TMD films.
Charge mobilities in the TMD films were significantly lower than those measured in individual TMD flakes. We study the possible factors limiting the performance of liquid-processed TMD FETs and discuss various defects in the TMD films: contacts between flakes, carbon contamination, sulfur vacancies etc. However, liquid-phase fabrication of TMD films opens a promising way for their industrial application.