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Layer-dependent band structure evolution of transition-metal dichalcogenides (TMDs) endows them with various bandgaps from insulating to semiconducting to conductive. Here, we demonstrate a metal–semiconductor–metal (MSM) photodetector using only TMD materials for both electrodes and photoactive materials. Semimetal few-layered PtSe2acts as metal electrodes, and monolayer WS2acts as a photoactive material. PtSe2was synthesized by thermally assisted selenization, and the device was fabricated by using photolithography coupled with direct laser patterning. By modifying the scanning step during the laser patterning process, various channel widths can be achieved. As-fabricated devices exhibit a satisfactory ON/OFF ratio and fair photoresponse. A comparison study shows that a device with a shorter channel width has better photoresponsivity. A back-to-back Schottky diode model estimates well the barrier height of the PtSe2/WS2heterojunction. The device also exhibits the lowering of barrier height with increasing laser power, owing to the photogating effect. Our study widens the material choices for 2D electrodes and investigates the feasibility of the low-cost laser patterning on the fabrication of optoelectronic devices.

Graphene has emerged as a promising material for optoelectronics due to its potential for ultrafast and broad-band photodetection. The photoresponse of graphene junctions is characterized by two competing photocurrent generation mechanisms: a conventional photovoltaic effect and a more dominant hot-carrier-assisted photothermoelectric (PTE) effect. The PTE effect is understood to rely on variations in the Seebeck coefficient through the graphene doping profile. A second PTE effect can occur across a homogeneous graphene channel in the presence of an electronic temperature gradient. Here, we study the latter effect facilitated by strongly localised plasmonic heating of graphene carriers in the presence of nanostructured electrical contacts resulting in electronic temperatures of the order of 2000 K. At certain conditions, the plasmon-induced PTE photocurrent contribution can be isolated. In this regime, the device effectively operates as a sensitive electronic thermometer and as such represents an enabling technology for development of hot carrier based plasmonic devices.

We report a CVD hexagonal boron nitride (hBN-) assisted transfer method that enables a polymer-impurity free transfer process and subsequent top encapsulation of large-area CVD-grown graphene. We demonstrate that the CVD hBN layer that is utilized in this transfer technique acts as a buffer layer between the graphene film and supporting polymer layer. We show that the resulting graphene layers possess lower doping concentration, and improved carrier mobilities compared to graphene films produced by conventional transfer methods onto untreated SiO2/Si, SAM-modified and hBN covered SiO2/Si substrates. Moreover, we show that the top hBN layer used in the transfer process acts as an effective top encapsulation resulting in improved stability to ambient exposure. The transfer method is applicable to other CVD-grown 2D materials on copper foils, thereby facilitating the preparation of van der Waals heterostructures with controlled doping.