Use of a Hexagonal\nBoron Nitride Interlayer for Noticeable\nEnhancement of Detectivity in Flexible Dual-Doped Graphene/WS<sub>2</sub> Heterojunction Photodetectors

Despite\na lot of studies on flexible broadband photodetectors (PDs)\nby employing two-dimensional (2D)-materials-based heterostructures,\ntheir performance enhancement is limited due to the high dark current\n(DC) originating from the low barrier at the heterojunctions. One\npromising approach to reduce the DC is to locate a high-band-gap low-dimensional\ninterfacial layer at the heterojunction interface as a blocking barrier.\nHere, we report the successful fabrication of an all-2D vertical heterojunction:\ndual-doped graphene (D-GR)/hexagonal boron nitride (h-BN)/WS<sub>2</sub> for flexible PD applications. Dual doping of graphene with Au nanoparticles\nand (trifluoromethanesulfonyl)amide impurities was done for lowering\nthe sheet resistance while maintaining the transmittance. The DC density\nis greatly suppressed (9.78 → 0.85 nA cm<sup>–2</sup> at zero bias) by inserting a h-BN layer at the D-GR/WS<sub>2</sub> heterojunction interface, thereby enhancing the detectivity by 17\ntimes (2.5 × 10<sup>9</sup> → 4.2 × 10<sup>10</sup> cm Hz<sup>1/2</sup> W<sup>–1</sup> at 410 nm) at zero bias,\nmeaning “self-powered”. We also compare other principal\nfigures-of-merit of the PDs without and with h-BN, such as the photocurrent/DC\nratio, diode quality, responsivity, and external quantum efficiency,\nand evaluate the response speed and mechanical stability.