We report the fabrication and optoelectronic characterization of field-effect transistors (FETs) based on few-layer ReSe2. The devices show n-type conduction due to the Cr contacts that form low Schottky barriers with the ReSe2 nanosheet. We show that the optoelectronic performance of these FETs is strongly affected by air pressure, and it undergoes a dramatic increase in conductivity when the pressure is lowered below the atmospheric one. Surface-adsorbed oxygen and water molecules are very effective in doping ReSe2; hence, FETs based on this two-dimensional (2D) semiconductor can be used as an effective air pressure gauge. Finally, we report negative photoconductivity in the ReSe2 channel that we attribute to a back-gate-dependent trapping of the photo-excited charges.

We studied the temperature dependent transport properties and memory behaviour of ultrathin black phosphorus field-effect transistors. The devices show electrical conductance and field-effect mobility that decreases with the rising temperature. The field effect mobility, which depends also on the gate voltage sweep range, is 283 cm2V-1s-1 at 150 K and reduces to 33 cm2V-1s-1 at 340 K, when the voltage gate sweep range is ± 50 V. The transfer characteristics show a hysteresis width that increases with the temperature and is exploited to enable non-volatile memories with a wider programming window at higher temperatures.

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We report the fabrication, electrical, and optical characterizations of few-layered black phosphorus (BP)-based field-effect transistor (FET). The fabricated device exhibits a p-type transport with hole mobility up to 175 cm2 V−1 s−1 at Vds = 1 mV. The transfer characteristics show a large hysteresis width that depends linearly on the gate voltage and decreases with the increasing drain bias. The fabricated device also ensures a non-volatile charge-trap memory behaviour, with a stable and long retention time. The material’s photodetection capabilities enhance the functionality of the device making it controllable by light. The photocurrent was observed to be linearly increasing with the light incident power and exposure time. As a photodetector, the transistor reaches a responsivity and detectivity up to 340 mA W−1 and 6.52 × 1011 Jones under white light at 80 $$\mathrm{mW}$$ mW , respectively. Time-resolved measurements provide evidence of a long single exponential decay process through deep intra-gap states. Our results highlight the potential of a few layers BP as a nanomaterial for field-effect, memory, and optoelectronic devices. Graphical Abstract

This study reports the optoelectronic characterization of few-layer ReSe 2 field effect transistors at different pressures. The output curves reveal dominant n-type behavior and a low Schottky barrier at the metal contacts. The transfer curves show a significant hysteresis that can be exploited in memory devices with an order ofmagnitude memory window and good cycling. The devices are dramatically affected by air pressure; their conductance and mobility increase with the lowering pressure that desorbs electronegative air molecules from the surface of the material. The photoresponse under white super-continuum laser illumination reveals that the device exhibits positive photoconductivity (PPC) at ambient and low (≈1 mbar) pressure and negative photoconductivity (NPC) in a higher vacuum (≈10 −4 mbar). The transition from PPC to NPC can be explained by considering that the photoresponse is affected by molecule desorption, which yields PPC at higher pressure, and defect trapping of photogenerated carriers, which can dominate at lower pressures. The transient behavior of the device exposed to laser pulses shows a faster response and a higher photodetection efficiency at ambient pressure, with the highest signal-to-noise ratio at the valley of the transfer curve between p-and n-type conduction.