Achieving a Noise Limit with a Few-layer WSe Avalanche Photodetector at Room Temperature.

We engineered a two-dimensional Pt/WSe/Ni avalanche photodetector (APD) optimized for ultraweak signal detection at room temperature. By fine-tuning the work functions, we achieved an ultralow dark current of 10 A under small bias, with a noise equivalent power (NEP) of 8.09 fW/Hz. This performance is driven by effective dark barrier blocking and a record-long electron mean free path (123 nm) in intrinsic WSe, minimizing dark carrier replenishment and suppressing noise under an ultralow electric field. Our APD exhibits a high gain of 5 × 10 at a modulation frequency of 20 kHz, effectively balancing gain and bandwidth, a common challenge in traditional photovoltaic-based APDs. By addressing the typical challenges of high noise and low gain and minimizing dependence on high electric fields, this work highlights the potential of 2D materials in developing efficient, low-power, and ultrasensitive photodetections.