The miniaturization of ferroelectric devices offers prospects for non-volatile memories, low-power electrical switches and emerging technologies beyond existing Si-based integrated circuits. An emerging class of ferroelectrics is based on van der Waals (vdW) two-dimensional materials with potential for nano-ferroelectrics. Here, we report on ferroelectric semiconductor junctions (FSJs) in which the ferroelectric vdW semiconductor α-In 2 Se 3 is embedded between two single-layer graphene electrodes. In these two-terminal devices, the ferroelectric polarization of the nanometre-thick In 2 Se 3 layer modulates the transmission of electrons across the graphene/In 2 Se 3 interface, leading to memristive effects that are controlled by applied voltages and/or by light. The underlying mechanisms of conduction are examined over a range of temperatures and under light excitation revealing thermionic injection, tunnelling and trap-assisted transport. These findings are relevant to future developments of FSJs whose geometry is well suited to miniaturization and low-power electronics, offering opportunities to expand functionalities of ferroelectrics by design of the vdW heterostructure.

The fabrication of solution-processed organic thin-film transistors (OTFTs) is the cleanest root for the development of green and eco-friendly disposable technologies as a crucial need of human society in the future. Therefore, P3HT polymer based OTFTs are demonstrated here with mobility as high as 8.0 cm2/(V·s) by using an unconventional solid–electrolyte layer containing the redox-active ionic compound ethyl viologen diperchlorate (EV­(ClO4)2) as the gate dielectric. A suitable negative gate bias produces a carrier density higher than 1015 holes/cm2 resulting from a reversible redox exchange reaction between EV2+ and P3HT present in the electrolyte and channel, respectively, other than the field effect and electrochemical doping. Anonymous high current (I G) between source and gate has been observed which is actually the redox-exchange current to produce large carrier density, which solely controls the operation of the transistors at very low operating voltage. A large specific capacitance (Ci = 7.1 μF/cm2) of the redox-electrolyte layer facilitates the OTFTs to operate below 1.5 V with bulk conductivity up to ∼194 S/cm and sheet conductance 40 μS/area. Our OTFT devices exhibit high reproducibility in performance and better devices parameters, including subthreshold swings down to 177 mV/dec and current ON/OFF ratios up to 107.

Ferroelectricity at the nanometre scale can drive the miniaturisation and wide application of ferroelectric devices for memory and sensing applications. The two-dimensional van der Waals (2D-vdW) ferroelectrics CuInP2S6(CIPS) has attracted much attention due to its robust ferroelectricity found in thin layers at room temperature. Also, unlike many 2D ferroelectrics, CIPS is a wide band gap semiconductor, well suited for use as a gate in field-effect transistors (FETs). Here, we report on a hybrid FET in which the graphene conducting channel is gated through a CIPS layer. We reveal hysteresis effects in the transfer characteristics of the FET, which are sensitive to the gate voltage, temperature and light illumination. We demonstrate charge transfer at the CIPS/graphene interface in the dark and under light illumination. In particular, light induces a photodoping effect in graphene that varies from n- to p-type with increasing temperature. These hybrid FETs open up opportunities for electrically and optically controlled memristive devices.

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