HgSe/CdE (E = S, Se) Core/Shell Nanocrystals by Colloidal Atomic Layer Deposition

Core/shell colloidal quantum dots (QDs) can have a more efficient photoluminescence than core-only QDs due to better surface passivation and a localization of the charge carriers in the core. Here, we demonstrate the synthesis of HgSe/CdS, HgSe/CdSe, and HgSe/CdSe/CdS core/shell QDs at room temperature by a succession of self-limiting half-reactions. A 2 detailed structural characterization through transmission electron microscopy analysis shows that shell growth happens in an additive manner. Each sequence of two half-reactions results in a approximate to 0.5 nm increase in shell thickness, meaning that approximately one monolayer is grown at the time. In all cases, shell growth eliminates the n-type doping that is intrinsic to HgSe QDs. In the case of HgSe/CdSe core/shell QDs, shell growth is strain-free as both materials have an almost identical lattice parameter. CdS shells, however, lead to the most pronounced increase of the photoluminescence quantum yield, reaching 16.5% after mild annealing for HgSe/CdS QDs emitting at around 0.69 eV (1.8 mu m).