Ultrafast Colloidal Quantum Dot Infrared Photodiode

Lead sulfide (PbS) colloidal quantum dots (QDs) have received attentions as materials for near-infrared (NIR) photodetection in view of their strong and tunable absorption in the NIR region and room-temperature solution processability. However, the realization of high-speed PbS QD photodetection has been severely hindered by the extremely low carrier mobility (similar to 10(-5) to 10(-2) cm(2) V-1 s(-1)). Here, an ultrafast PbS QD photodiode fabricated with low mobility QDs (similar to 10(-3) cm(2) V-1 s(-1)) is demonstrated, which has rise/fall times as short as 0.33 mu s at zero voltage bias. The fast response is achieved by engineering resistor-capacitor (RC) time delay and charge transport in the device. The photodiode also has an external quantum efficiency (EQE) exceeding 100% under voltage bias, which is possibly due to the photoconductive gain induced by hole transport layer (HTL). The photoconductive gain combined with low noise current enables high sensitivity with a specific detectivity value up to 3.2 x 10(11) Jones at 1125 nm.