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. We show with
computational modeling that native InP QD surface oxides give rise
to 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 edge that resembles defect-free, stoichiometric
InP. We then developed a synthetic strategy using stoichiometric amounts
of common atomic layer deposition precursors in alternating cycles
to achieve layer-by-layer growth. Metal-oxide-shelled InP QDs show
bulk and local structural perturbations as determined by X-ray diffraction
and extended X-ray absorption fine structure spectroscopy. Upon growing
ZnSe shells of varying thickness on the oxide-shelled QDs, we observe
increased photoluminescence (PL) quantum yields and narrowing of the
emission linewidths that we attribute to decreased ion diffusion to
the shell, as supported by phosphorus X-ray emission spectroscopy.
These results present a versatile strategy to control QD interfaces
for novel heterostructure design by leveraging surface oxides. This
work also contributes to our understanding of the connections between
structural complexity and PL properties in technologically relevant
colloidal optoelectronic materials.