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Recently, WS2 has been considered a promising photodetector material due to its benefits of atomic thickness, easily customized single-crystal van der Waals heterostructure, and efficient photon absorption. However, the photosensitivity obtained from the WS2 photodetector is still unsatisfactory. Therefore, this article proposes a WS2-based high sensitivity field-effect transistor (FET) based on avalanche multiplication. Under 532-nm illumination, WS2 FET has ultralow dark current ($10^{-{12}}$ A), high responsivity (74 A/W), and high detectivity ($1.45\times 10^{{13}}$ Jones). In addition, the avalanche breakdown voltage of the device is reduced by employing graphene as an electrode. Because the height of the Schottky barrier can be reduced by replacing the Au electrode with a graphene electrode, the lower Schottky barrier can result in higher electric field intensity in the WS2 channel. Meanwhile, the unique transfer and output characteristics are observed in WS2 FET with graphene electrode. The inherent mechanisms are discussed, considering the Fermi-level tenability of graphene flakes and ambipolar transport properties of WS2. These results open a promising door to realize the WS2 FET with low power consumption and ultrahigh photoresponsivity, which will be ideal for high-performance photodetectors. [ABSTRACT FROM AUTHOR]

Au nanoparticles (NPs) were drop-casted onto germanium (Ge) devices to investigate the influence of Au NPs on the electronic transport and photodetection properties of Ge metal–semiconductor–metal photodetectors. A significant hysteresis behavior was observed in the current–voltage curves of the Au NP-decorated Ge photodetector, which was ascribed to the energy band bending below the Au NPs and the electrostatic effect of image charges in the Au NPs. More interestingly, at the optical communication wavelength of $1.55~\mu \text{m}$ , the introduction of Au NPs effectively improved the responsivity of the device from 0.18 to 0.92 A/W. Rather than the localized surface plasmon resonance effect, the increase of responsivity in the Au NP-decorated Ge photodetector was caused by a type-II liked energy band alignment, which enhanced the spatial electron–hole separation effect. These results provide inspiration for the development of novel optoelectronic devices. [ABSTRACT FROM AUTHOR]