Colloidal, Room Temperature Growth of Metal Oxide Shells on InP Quantum Dots

We demonstrate colloidal, layer-by-layer growth of metal oxide shells on InP quantum dots (QDs) at room temperature. First, computational modeling demonstrates that native InP surface oxides give rise to increased nonradiative pathways due to the presence of surface-localized dark states near the band edges. Replacing surface indium with zinc to form a ZnO shell results in reduced nonradiative decay and a density of states at the valence band maximum that resembles defect-free, stoichiometric InP. Motivated by these findings, we developed a synthetic strategy using stoichiometric amounts of common ALD precursors in alternating cycles. Metal oxide-shelled InP QDs show bulk and local structural perturbations as determined by X-ray diffraction extended X-ray absorption fine structure spectroscopy. Upon growing ZnSe shells of varying thickness on the oxide-shelled QDs, we observe increased photoluminescence quantum yields and narrowing of the emission linewidths, which we hypothesize to be attributable to decreased ion diffusion to the shell, as supported by P X-ray emission spectroscopy. These results present a generalizable and versatile strategy to control QD interfaces for novel heterostructure design by leveraging surface oxides. This work also contributes to our understanding of how to use structural complexity for improved PL properties of technologically relevant colloidal optoelectronic materials.