Dendritic WS₂ Nanocrystal-Coated Monolayer\nWS₂ Nanosheet Heterostructures for Phototransistors

Abstract

Two-dimensional\ntungsten disulfide (WS₂), as one of\nthe widely concerned members of the transition metal dichalcogenides\nfamily, has been studied broadly by its outstanding photonic and electronic\nproperties. Since all of the research works focus on size and the\nnumber of layers, the dendritic structure WS₂ has been\nscarcely reported. In our study, we make use of atmospheric pressure\nchemical vapor deposition (APCVD) to control the synthesis of dendritic\nWS₂/monolayer WS₂ heterostructures on the SiO₂/Si substrate. The stacking morphology of the heterostructure\nis verified by AFM, Raman, and PL spectra. The effects of growth times\nand carrier gas flux on the quasi-epitaxial growth of WS₂ films with dendritic structures have been systematically studied.\nIn addition, the transition between fractal, dendritic, and compact\nmorphologies with the increase of the growth times (carrier gas flux)\nare more significant. The compact morphology and difference of contact\npotential between the adjacent dendritic structures are characterized\nby Kelvin probe force microscopy (KPFM). Moreover, the as-fabricated\nFET devices exhibit excellent electronic properties (on/off ratio,\ncarrier mobility, photoresponsivity, and response time are about 10⁶, 11.42 cm² V^–1S^1–, 46.6 mA/W, and 105.5 μs, respectively). This study paves\nthe way for the rational design of high-sensitivity fractal-enhanced\nphototransistor devices for industrial and commercial applications.