Title: Organic photodiode integration on Si substrate beyond 1000 nm wavelength

Abstract

Near infrared (NIR) and shortwave infrared (SWIR) image technologies are of interest for many emerging applications. Above 1100 nm, Si is blind and has no sensitivity. Emerging optoelectronic materials, such as small molecules, polymer, and organic-inorganic hybrids have been demonstrated as promising alternatives to traditional inorganic photodetectors for NIR and shortwave infrared (SWIR) imaging. Among photodetector technologies, organic photodetectors (OPDs) are groundbreaking light sensors with unique photon-to-electron responses at various wavelengths that offer limitless flexibility in field applications due to the tunable design of organic semiconductors. Organic photodiode integration on the Si readout circuit offers a solution for extending the sensitivity beyond 1000 nm. In this work, we report the way to integrate organic photodiode on Si substrate with metals that are CMOS process compatible as bottom electrodes, such as titanium nitride (TiN), tungsten (W), and aluminum (Al). We report high-efficiency NIR sensor enabled by employing TiN and W as bottom electrodes, with an external quantum efficiency (EQE) of ~50% at 940 nm and ~70% at 1030 nm, a dark leakage current density of 15 nA/cm2, a bandwidth of 15 kHz at -4V, and a dynamic range (DR) of ~100 dB are achieved. Low resistivity and inert properties of TiN make it forms a good interface with organic active layer, leading to an ideal bottom contact metal for organic photodiode when integrated on Si substrate. This work highlights the importance of the interface between the bottom electrode and OPD, which needs to be well considered for OPD and Si-CMOS integration with a CMOS compatible process flow, offering the possibility to extend the sensitivity of CMOS image sensor beyond 1000 nm, which can be applied in high-performance NIR/SWIR low-cost imaging systems.