Gate Voltage Dependence Ultrahigh Sensitivity WS₂ Avalanche Field-Effect Transistor

Recently, WS
₂
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 WS
₂
photodetector is still unsatisfactory. Therefore, this article proposes a WS
₂
-based high sensitivity field-effect transistor (FET) based on avalanche multiplication. Under 532-nm illumination, WS
₂
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 WS
₂
channel. Meanwhile, the unique transfer and output characteristics are observed in WS
₂
FET with graphene electrode. The inherent mechanisms are discussed, considering the Fermi-level tenability of graphene flakes and ambipolar transport properties of WS
₂
. These results open a promising door to realize the WS
₂
FET with low power consumption and ultrahigh photoresponsivity, which will be ideal for high-performance photodetectors.