Platinum diselenide (PtSe₂) field‐effect transistors with ultrathin channel regions exhibit p‐type electrical conductivity that is sensitive to temperature and environmental pressure. Exposure to a supercontinuum white light source reveals that positive and negative photoconductivity coexists in the same device. The dominance of one type of photoconductivity over the other is controlled by environmental pressure. Indeed, positive photoconductivity observed in high vacuum converts to negative photoconductivity when the pressure is raised. Density functional theory calculations confirm that physisorbed oxygen molecules on the PtSe₂ surface act as acceptors. The desorption of oxygen molecules from the surface, caused by light irradiation, leads to decreased carrier concentration in the channel conductivity. The understanding of the charge transfer occurring between the physisorbed oxygen molecules and the PtSe₂ film provides an effective route for modulating the density of carriers and the optical properties of the material.

This study reports the optoelectronic characterization of few‐layer ReSe₂field 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.

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.

Herein, the fabrication and electrical characterization of multilayer black phosphorus (BP)‐based field effect transistors with Ni or NiCr alloy contacts are reported. The devices show p‐type conduction and hysteresis in the transfer characteristics that enable their use as nonvolatile memories. The differences between Ni and NiCr contacts are investigated and the Y‐function method is applied to extract the channel mobility up to 112 cm² V⁻¹ s⁻¹ and the contact resistances. Ni contacts present specific contact resistance of 6.3 k Ω μm that increases to 18.1 k Ω μm for NiCr. These findings are important for the technological exploitation of multilayer BP in a new class of electronic and optoelectronic devices.