OFF State Reliability Challenges of Monolayer WS2 FET Photodetector: Impact on the Dark and Photo-Illuminated State

This work reports the hot-hole injection-originated instability in the electrical characteristics (or the photodetection performance) of a monolayer WS2 Field Effect Transistor (FET) photodetector. When a reverse bias (i.e., OFF-state bias or negative gate voltage) temporal stress with a lateral electric field is applied under visible light illumination, the photocurrent is found to vary with time by up to 1 to 2 orders of magnitude. Instability in the dark current is also observed post the stress under illumination, which is reflected in the variation in the transfer and the output characteristics of the FET. The observations impose severe limitations on the reverse-biased back-gated FET for sensitive photodetection applications using transparent single-layer WS2 as the photoactive material.