Near IR Organic Photodetectors with Plasmonic Nanogap Coplanar Electrodes for Integrated Photonic Circuit

Near-infrared (NIR) light sensing is important in various applications, such as integrated photonics, and optical computing. Organic photodetectors (OPDs) based on low-bandgap organic semiconductors have emerged as promising candidates for NIR photodetection due to their excellent NIR absorption properties and solution processability. However, the conventional OPD structures based on a cross-bar array suffer from low responsivity to NIR light, array crosstalk, and difficult on-chip integration with photonic components. In this study, we propose a novel architecture for NIR OPDs with nanogap planar electrodes, specifically designed for integrated photonic circuits. The photoactive channel, featuring a nanogap of approximately 20 nm, was fabricated through the selective peel-off of a surface-modified metal electrode with a self-assembled monolayer. Our results show that the proposed nanogap OPDs with a bulk-heterojunction active layer exhibited high performance for 830 nm light, despite having an extremely small photoactive area. We found that the nanogap induced a plasmonic effect, enhancing light absorption in the photoactive channel. Various blend compositions of the bulk-heterojunction were investigated to understand the working principle of this device and determine the optimal performance conditions. Finally, as a proof of concept, the nanogap OPDs coupled with a waveguide demonstrated optical-to-electronic signal modulation on an integrated Si photonic device.