Asymmetric Dressing of WSe₂ with (Macro)molecular Switches: Fabrication of Quaternary-Responsive Transistors

The forthcoming saturation of Moore's law has led to a strong demand for integrating analogue functionalities within semiconductor-based devices. As a step toward this goal, we fabricate quaternary-responsive WSe₂-based field-effect transistors (FETs) whose output current can be remotely and reversibly controlled by light, heat, and electric field. A photochromic silane-terminated spiropyran (SP) is chemisorbed on SiO₂ forming a self-assembled monolayer (SAM) that can switch from the SP to the merocyanine (MC) form in response to UV illumination and switch back by either heat or visible illumination. Such a SAM is incorporated at the dielectric-semiconductor interface in WSe₂-based FETs. Upon UV irradiation, a drastic decrease in the output current of 82% is observed and ascribed to the zwitterionic MC isomer acting as charge scattering site. To provide an additional functionality, the WSe₂ top surface is coated with a ferroelectric co-polymer layer based on poly(vinylidene fluoride-co-trifluoroethylene). Because of its switchable inherent electrical polarization, it can promote either the accumulation or depletion of charge carriers in the WSe₂ channel, thereby inducing a current modulation with 99% efficiency. Thanks to the efficient tuning induced by the two components and their synergistic effects, the device polarity could be modulated from n-type to p-type. Such a control over the carrier concentration and device polarity is key to develop 2D advanced electronics. Moreover, the integration strategy of multiple stimuli-responsive elements into a single FET allows us to greatly enrich its functionality, thereby promoting the development for More-than-Moore technology.