Selective p-Doping of 2D WSe2 via UV/Ozone Treatments and Its Application in Field-Effect Transistors.

Development of two-dimensional (2D) semiconductor devices with good Ohmic contact is essential to utilize their full potential for nanoelectronics applications. Among the methods that have been introduced to reduce the Schottky barrier in 2D material-based electronic devices, charge transfer doping has attracted significant interest because of its efficiency, simplicity, and compatibility with the microelectronic fabrication process. In this study, 2D WSe2-based field-effect transistors (FETs) were subjected to selective UV/ozone treatment to improve the Ohmic contact by forming WOX with a high work function, which induced hole doping in the neighboring WSe2 via electron transfer. The atomic force microscopy, cross-sectional transmission electron microscopy, and micro-Raman spectroscopy analyses confirmed the self-limiting formation of WOX while maintaining the crystallinity of the underlying WSe2. The channel layer of the back-gated 2D WSe2 FETs was encapsulated using 2D hexagonal boron nitride to prevent the UV/ozone-induced oxidation. By contrast, the regions that were in contact with the underlying metal electrodes were open, which allowed area-selective p-doping in the 2D WSe2. Our study demonstrated that the Ohmic-like behaviors obtained after area-selective UV/ozone treatment improved the electrical properties of the 2D WSe2-based FETs such as the field-effect mobility (improvement of 3-4 orders of magnitude) and current on/off ratio (improvement of five orders of magnitude), while maintaining the p-type normally-off characteristics. These results provide useful insights into an effective and facile method to reduce contact resistance in 2D semiconductor materials, thereby enhancing the electrical performances of 2D material-based electronic devices.