Work-Function Engineering of Graphene Electrodes by Self-Assembled Monolayers for High-Performance Organic Field-Effect Transistors

We have devised a method to optimize the performance of organic field-effect transistors (OFETs) by controlling the work functions of graphene electrodes by functionalizing the surface of SiO₂ substrates with self-assembled monolayers (SAMs). The electron-donating NH₂-terminated SAMs induce strong n-doping in graphene, whereas the CH₃-terminated SAMs neutralize the p-doping induced by SiO₂ substrates, resulting in considerable changes in the work functions of graphene electrodes. This approach was successfully utilized to optimize electrical properties of graphene field-effect transistors and organic electronic devices using graphene electrodes. Considering the patternability and robustness of SAMs, this method would find numerous applications in graphene-based organic electronics and optoelectronic devices such as organic light-emitting diodes and organic photovoltaic devices

Photoelectric Memory Effect in Graphene Heterostructure Field-Effect Transistors Based on Dual Dielectrics

We report a photo and field (PF)-induced doping of a graphene-heterostructure field-effect transistor (graphene HFET) using a double-layered gate insulator consisting of narrow-bandgap insulator (NGI) and wide-bandgap insulator (WGI). The PF-induced doping in the graphene HFETs with variable NGIs (hafnium oxide, silicon nitride, and hexagonal boron nitride) are investigated, and consequently we reveal that this rewritable/erasable doping behavior is not limited to specific insulating materials, but unexceptionally accomplished when a step-like vertical band diagram, that is graphene/NGI/WGI, is fulfilled in the device. We clearly verify that this doping is originated from PF-induced charge transfer between graphene and defects at the NGI/WGI interface, and then the polarized charges at the NGI/WGI interface pretend to be “remote dopants”, shifting Dirac voltage of the device. The remote dopant is highly stable in the dark due to the presence of the adjacent insulators providing enormous energy barriers, but can be efficiently tuned by the modulation of the gate bias and incident photon energy. Because the PF-induced doping mechanism is not limited by specific materials that is still hard to be synthesized as a large scale, the graphene HFET memory devices can be patterned with a large scale using practical fabrication processes, appealing to industrial applications