Quantum dot photodiodes fabricated by electrostatic layer-by-layer self-assembly

In this paper we demonstrate photodiodes based on Schottky junction between multilayers of CdTe quantum dots (QDs) and thermally evaporated Au thin film. The CdTe QDs are synthesized and dispersed in aqueous solution with either positively (amino group) or negatively (carboxylate group) charged capping ligands. By electrostatic attraction, the QDs are self-assembled layer-by-layer on a silane functionalized substrate. By changing the number of layers, the thickness of the QD thin film can be well controlled. For the photodiode with 180 nm-thick CdTe QD thin film, external quantum efficiency = 1.38% can be achieved under 405 nm laser illumination and applied voltage = 10 V.