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 spincoating 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 d B, and a bandwidth(-3 dB) of 10 k Hz. 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 selfpowered Au/PEDOT:PSS/Ge/Ag PD will be highly suitable for NIR imaging.