Atomic Scale Composite Oxides Infiltration to Quantum Dot Photodetector with Ultralow Dark Current

Lead sulfide quantum dots (QDs) photodetectors have received wide attention due to the merits of low-cost manufacturing, tunable bandgap, and the compatibility with flexible substrates. Currently, the QDs photodetectors fabricated via ligand exchange approaches suffer from a large dark current, which affects the overall performance. Herein, a precisely controlled atomic scale composite oxide infiltration method is developed to modify the QDs films via atomic layer deposition (ALD). The oxide infiltration enhances the electron coupling between QDs, lifts the photocurrent through effective electron transfer, and passivates the surface traps. At the same time, in situ characterizations show that ALD precursors directionally insert with the surface ligands of the QDs; thus, during the ALD process, the organic ligands remain attached to the surface of PbS QDs. The existence of long chain organic ligands which have a longer delivery distance guarantees the ultralow dark current (0.07 nA under bias voltage of 10 V) and high detectivity. In addition, ZnO is introduced to fill the QDs films via ALD to form the Al2O3/ZnO composite structure. ZnO has a higher carrier mobility which further improves the efficiency of electron transfer and enhances the photocurrent while maintaining the ultralow dark current.