Abstract
In this study, we investigated the p-doping effects of a fluoropolymer, Cytop, on tungsten diselenides (WSe2). The hole current of the Cytop–WSe2 field-effect transistor (FET) was boosted by the C–F bonds of Cytop having a strong dipole moment, enabling increased hole accumulation. Analysis of the observed p-doping effects using atomic force microscopy (AFM) and Raman spectroscopy shed light on the doping mechanism. Moreover, Cytop reduces the electrical instability by preventing the adsorption of ambient molecules on the WSe2 surface. Annealing Cytop deposited on WSe2 eliminated the possible impurities associated with adsorbates (i.e., moisture and oxygen) that act as traps on the surface of WSe2. After thermal annealing, the Cytop–WSe2 FET afforded higher p-type conductivity and reduced hysteresis. The combination of the Cytop–WSe2 FET with annealing provides a promising method for obtaining high-performance WSe2 p-type transistors.
Highlights
Transition-metal dichalcogenides (TMDs) are used as channel materials that can overcome the limitations of existing silicon devices, with controllable bandgaps, atomically thin 2D structures, and compact metal and chalcogen lattice structures [1,2,3]
The large amount of fluorine contained in Cytop can diffuse as the C–F bonds are more aligned on the WSe2 surface, resulting in a large downward shift of the Fermi level, and the p-doping effect becomes stronger
A simple and stable p-doping technique was proposed by coating WSe2 with Cytop, an amorphous fluorinated polymer
Summary
Transition-metal dichalcogenides (TMDs) are used as channel materials that can overcome the limitations of existing silicon devices, with controllable bandgaps, atomically thin 2D structures, and compact metal and chalcogen lattice structures [1,2,3]. Because the Fermi level of WSe2 is close to the middle of the bandgap [11], it is difficult to inject holes or electron carriers between the contact metal and WSe2 These issues limit the effective carrier mobility and lead to poor process yields and non-uniform properties [12]. When TMDs are exposed to NO2 or K gas, their electrical properties can be adjusted depending on the exposure concentration or time [13,14] These methods involve complex processes and are limited in that the doping effect cannot be stably maintained for a sufficiently long time. 4% variation in Vth and 19% variation in μhole due to air-exposure effects)
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