Palladium diselenide (PdSe₂), a stable layered material with pentagonal structure, has attracted extensive interest due to its excellent electrical and optoelectronic performance. Here, we report a reliable process to synthesize PdSe₂ via chemical vapor deposition (CVD) method. Through systematic regulation of temperature in the growth process, we can tune the thickness, size, nucleation density and morphology of PdSe₂ nanosheets. Field-effect transistors based on PdSe₂ nanosheets exhibit n-type behavior and present a high electron mobility of 105 cm²·V^-1·s^-1. The electrical property of the devices after 6 months keeping in the air show little change, implying outstanding air-stability of PdSe₂. In addition, PdSe₂ near-infrared photodetector shows a photoresponsivity of 660 A·W^-1 under 914 nm laser. These performances are better than those of most CVD-grown 2D materials, making ultrathin PdSe₂ a highly qualified candidate material for next-generation optoelectronic applications.

Doping, which is the intentional introduction of impurities into a material, can improve the metal-semiconductor interface by reducing Schottky barrier width. Here, we present high-quality two-dimensional SnS₂ nanosheets with well-controlled Sb doping concentration via direct vapor growth approach and following micromechanical cleavage process. X-ray photoelectron spectroscopy (XPS) measurement demonstrates that Sb contents of the doped samples are approximately 0.22%, 0.34% and 1.21%, respectively, and doping induces the upward shift of the Fermi level with respect to the pristine SnS₂. Transmission electron microscopy (TEM) characterization exhibits that Sb-doped SnS₂ nanosheets have a high-quality hexagonal symmetry structure and Sb element is uniformly distributed in the nanosheets. The phototransistors based on the Sb-doped SnS₂ monolayers show n-type behavior with high mobility which is one order of magnitude higher than that of pristine SnS₂ phototransistors. The photoresponsivity and external quantum efficiency (EQE) of Sb-SnS₂ monolayers phototransistors are approximately three orders of magnitude higher than that of pristine SnS₂ phototransistor. The results suggest that the method of reducing Shottky barrier width to achieve high mobility and photoresponsivity is effective, and Sb-doped SnS₂ monolayer has significant potential in future nanoelectronic and optoelectronic applications.

Two-dimensional (2D) van der Waals (vdWs) metal-semiconductor heterostructures with atomically sharp interface and matched work functions have recently attracted great attention due to their unique electronic and optoelectronic properties.Here we report the vapor phase epitaxial growth of large-scale vertical Sb/WSe₂ metal-semiconductor vdWs heterostructures with uniform stacking orientation. Compared with the growth on SiO₂/Si substrate, the thickness of Sb nanosheet on WSe₂ can be reduced effectively to monolayer.We construct Sb-WSe₂-Au asymmetric electrodes photodiode based on the Sb/WSe₂ heterostructures.Electrical transport measurements indicate that the photodiode show obvious rectifying effect.Optoelectronic characterizations show prominent photoresponse with a high photoresposivity of 364 mA/W, a fast response time of less than 8 ms, a large open-circuit voltage of 0.27 V and a maximum electrical power output of 0.11 nW.The direct growth of high-quality metal-semiconductor vdWs heterostructures may open up new realms in 2D functional electronics and optoelectronics.