Control of Chemical Doping-Mediated Space Charge for Energetic Band-Switching Modulation in Low-Noise Shortwave-Infrared Organic Photodetector.

This study investigates the influence of chemical doping on the spatial-charge distributions and carrier-tunneling mechanisms in single-polymer shortwave-infrared (SWIR) photomultiplication (PM)-organic photodetectors (OPDs). By systematically analyzing the optical and photoelectric properties influenced by chemical doping, it is identified that dopant-induced defects as space charges significantly contribute to Fowler-Nordheim (FN) tunneling, thereby impacting the performance of SWIR OPDs. At a doping concentration of 0.5 mm, the formation of positively charged carriers (polarons and/or bipolarons) within the polymer matrix initiates, thereby facilitating SWIR absorption and contributing to the balance between photocurrent and noise by mitigating FN tunneling through the reduction of defect density (N). However, as the doping concentration exceeds 5 mm, the increased N accumulates more space charge, accelerating FN tunneling. This enhances photocurrent generation and amplifies noise disproportionately, ultimately limiting OPD performance. Under N-minimized optimum doping concentration (at 0.5 mm), the OPD exhibited a noise equivalent power of 9.85 pW (at -8 V, bandwidth = 1 Hz, and wavelength = 1490 nm), and a linear dynamic range of 42 dB. These findings demonstrate the role of chemical doping in enhancing the performance of SWIR PM-OPDs, paving the way for advanced photonic sensors.