Low-power organic electronics based on gate-tunable injection barrier in vertical graphene-organic semiconductor heterostructures

Novel device architectures based on heterostructures of graphene with semiconductor layers have recently attracted considerable interest due to their potential in a wide range of electronic and photonic applications. The key concept in these devices is to exploit the work function tunability of graphene via external gate field to modulate the current flow across the graphene-semiconductor junction by adjusting the Schottky barrier height. Transistor devices based on a vertical heterojunction of graphene with inorganic semiconductors (n- and p-type Silicon) [1], oxide semiconductor (n-type indium gallium zinc oxide) [2,3] and flakes of 2D layered materials (molybdenum disulfide, tungsten disulfide) [4-7] have been successfully fabricated with a high on/off ratio, overcoming the limitation of planar graphene field-effect devices. We demonstrate, for the first time, low-voltage complementary p- and n-channel vertical organic thin film transistors (VOTFTs) based on the graphene-organic semiconductor heterojunctions with simple, scalable and low-temperature fabrication process. VOTFT device with thin layer of prototypical n-type organic semiconductor C₆₀ exhibits high on-current densities in the range of 10 mA/cm² with the driving voltage of only 1 V suppressing the output current of traditional planar organic field-effect transistors. It can also operate at the bias as low as 200 mV with high on/off ratio (~10³). For low-power logic application, complementary VOTFT devices with prototypical p-type organic semiconductors (CuPc, Pentacene, α-6T, Rubrene) are also investigated.