Self-powered and broadband germanium/PEDOT:PSS heterojunction photodetectors for near-infrared biomedical imaging applications

To develop high-performance photodetectors (PDs) as near-infrared (NIR) imaging sensors, researchers have either proposed new photoelectric materials, introduced complicated interface-processing steps, or created complex optical structures. In this study, we introduce a solution-processed organic material, PEDOT:PSS (PEDOT corresponds to a polymer of 3,4-ethylene dioxythiophene (EDOT), and PSS corresponds to a polystyrene sulfonate), to germanium (Ge) wafers using a convenient spin-coating method to improve the photoresponse performance of Ge-based PDs. The Ge wafers and PEDOT:PSS form a heterojunction that reduces the dark current when compared with the Ge Schottky PD (Au/Ge/Ag PD). The experimental results show that the Au/PEDOT:PSS/Ge/Ag heterojunction PD with a bias voltage of 0 V at 1550 nm exhibits a responsivity (R) of 0.26 A/W, a detectivity (D*) of 6.5×1011 Jones, a linear dynamic range (LDR) of 124 dB, and a bandwidth (−3 dB) of 10 kHz. This implies that the performance of the PD is comparable to that of previously reported Ge-based PDs. Subsequently, a biomedical imaging application of the PD is successfully demonstrated through foreign-body detection. Therefore, it is expected that the self-powered Au/PEDOT:PSS/Ge/Ag PD will be highly suitable for NIR imaging.