Ultralow Gain-Normalized Dark Current Density in a Colloidal Quantum Dot Avalanche Photodiode with a SACM Architecture

Short-wave infrared (SWIR) avalanche photodiodes (APDs) are important for LiDAR, free-space optical communication, and low-light imaging. Colloidal quantum dots (CQDs) offer a solution-processable, silicon-compatible SWIR platform, but conventional CQD p-i-n APDs couple photon absorption and avalanche multiplication in the same narrow-bandgap layer, causing severe dark-current growth under high reverse bias. Here, we demonstrate a CQD/i-ZnO APD based on a separate-absorption-charge-multiplication (SACM) architecture. By relocating the high-field multiplication region from the narrow-bandgap CQD absorber to wide-bandgap i-ZnO, this design suppresses tunneling-induced dark current while retaining avalanche multiplication. The optimized device achieves a gain-normalized dark current density of 4.86 × 10 –7 A cm –2, the lowest reported among CQD photodetectors with internal gain, and a specific detectivity of 1.15 × 10 12 Jones. These results establish SACM field engineering as an effective route toward low-dark-current CQD-based SWIR APDs.