Interface-Engineered Organic Near-Infrared Photodetector for Imaging Applications

Abstract

We report a high-speed low dark current near-infrared(NIR) organicphotodetector (OPD) on a silicon substrate with amorphous indium galliumzinc oxide (a-IGZO) as the electron transport layer (ETL). In-depthunderstanding of the origin of dark current is obtained using an elaborateset of characterization techniques, including temperature-dependentcurrent-voltage measurements, current-based deep-level transient spectroscopy(Q-DLTS), and transient photovoltage decay measurements. These characterizationresults are complemented by energy band structures deduced from ultravioletphotoelectron spectroscopy. The presence of trap states and a strongdependency of activation energy on the applied reverse bias voltagepoint to a dark current mechanism based on trap-assisted field-enhancedthermal emission (Poole-Frenkel emission). We significantlyreduce this emission by introducing a thin interfacial layer betweenthe donor: acceptor blend and the a-IGZO ETL and obtain a dark currentas low as 125 pA/cm(2) at an applied reverse bias of -1V. Thanks to the use of high-mobility metal-oxide transport layers,a fast photo response time of 639 ns (rise) and 1497 ns (fall) isachieved, which, to the best of our knowledge, is among the fastestreported for NIR OPDs. Finally, we present an imager integrating theNIR OPD on a complementary metal oxide semiconductor read-out circuit,demonstrating the significance of the improved dark current characteristicsin capturing high-quality sample images with this technology.