High Mobility Transistors and Flexible Optical Synapses Enabled by Wafer-Scale Chemical Transformation of Pt-Based 2D Layers.

Electronic devices employing two-dimensional (2D) van der Waals (vdW) transition-metal dichalcogenide (TMD) layers as semiconducting channels often exhibit limited performance (e.g., low carrier mobility), in part, due to their high contact resistances caused by interfacing non-vdW three-dimensional (3D) metal electrodes. Herein, we report that this intrinsic contact issue can be efficiently mitigated by forming the 2D/2D in-plane junctions of 2D semiconductor channels seamlessly interfaced with 2D metal electrodes. For this, we demonstrated the selectively patterned conversion of semiconducting 2D PtSe 2 (channels) to metallic 2D PtTe 2 (electrodes) layers by employing a wafer-scale low-temperature chemical vapor deposition (CVD) process. We investigated a variety of field-effect transistors (FETs) employing wafer-scale CVD-2D PtSe 2 /2D PtTe 2 heterolayers and identified that silicon dioxide (SiO 2 ) top-gated FETs exhibited an extremely high hole mobility of ∼120 cm 2 V -1 s -1 at room temperature, significantly surpassing performances with previous wafer-scale 2D PtSe 2 -based FETs. The low-temperature nature of the CVD method further allowed for the direct fabrication of wafer-scale arrays of 2D PtSe 2 /2D PtTe 2 heterolayers on polyamide (PI) substrates, which intrinsically displayed optical pulse-induced artificial synaptic behaviors. This study is believed to vastly broaden the applicability of 2D TMD layers for next-generation, high-performance electronic devices with unconventional functionalities.