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_D). However, as the doping concentration exceeds 5 mm, the increased N_D accumulates more space charge, accelerating FN tunneling. This enhances photocurrent generation and amplifies noise disproportionately, ultimately limiting OPD performance. Under N_D-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.