Use of a Hexagonal Boron Nitride Interlayer for Noticeable Enhancement of Detectivity in Flexible Dual-Doped Graphene/WS₂ Heterojunction Photodetectors

Despite a lot of studies on flexible broadband photodetectors (PDs) by employing two-dimensional (2D)-materials-based heterostructures, their performance enhancement is limited due to the high dark current (DC) originating from the low barrier at the heterojunctions. One promising approach to reduce the DC is to locate a high-band-gap low-dimensional interfacial layer at the heterojunction interface as a blocking barrier. Here, we report the successful fabrication of an all-2D vertical heterojunction: dual-doped graphene (D-GR)/hexagonal boron nitride (h-BN)/WS2 for flexible PD applications. Dual doping of graphene with Au nanoparticles and (trifluoromethanesulfonyl)amide impurities was done for lowering the sheet resistance while maintaining the transmittance. The DC density is greatly suppressed (9.78 → 0.85 nA cm–2 at zero bias) by inserting a h-BN layer at the D-GR/WS2 heterojunction interface, thereby enhancing the detectivity by 17 times (2.5 × 109 → 4.2 × 1010 cm Hz1/2 W–1 at 410 nm) at zero bias, meaning “self-powered”. We also compare other principal figures-of-merit of the PDs without and with h-BN, such as the photocurrent/DC ratio, diode quality, responsivity, and external quantum efficiency, and evaluate the response speed and mechanical stability.