Overcoming the sensitivity-speed trade-off in two-dimensional photodetectors via a functional oxide interlayer

Photodetectors that can achieve both high sensitivity and fast speed remain a challenge due to inherent trade-offs, particularly limiting in photonic integrated circuits. While substantial progress has been made in broadening spectral response, few strategies have directly addressed the simultaneous enhancement of sensitivity and speed. Here, we introduce a two-dimensional photodetector incorporating a functional interlayer, monolayer tungsten oxyselenide (TOS), formed between n-type PdPSe and p-type WSe₂. TOS serves multifunctional roles to overcome the trade-offs: suppressing dark current as a hole barrier, enhancing responsivity via photogating, and preserving speed through trap-assisted tunneling and direct tunneling. Under spatially resolved illumination, the device shows a detectivity (D*) of 3.78 × 10¹⁵ Jones at 520 nm, with a bandwidth of 0.055 GHz at 785 nm. When integrated onto a silicon photonic platform, it achieves D* of 3.69 × 10¹¹ Jones and a bandwidth of 0.11 GHz at 785 nm, outperforming most reported on-chip photodetectors. These results establish a route to sensitive, high-speed photodetectors for optical interconnect, communications, and sensing applications.