Design of Zn Chalcogenide Shells for Emissive Ga-Rich In_1–<i>X</i>Ga_<i>X</i>As Quantum Dots Synthesized in Molten Salts

Colloidal quantum dots (QDs) have seen expanded applications in optoelectronics from visible to near-infrared (NIR) wavelengths. However, the options for QDs with bright and size-tunable emission in the NIR region are mostly limited to heavy-metal-based (Pb, Cd, Hg) semiconductors. Here, Ga-rich In_1-<i>X</i>Ga_<i>X</i>As QDs with zinc chalcogenide shells are demonstrated as candidates for NIR emitters. Based on new developments in inorganic molten salt chemistry, we synthesized colloidal In_1-<i>X</i>Ga_<i>X</i>As QDs containing up to 85% gallium with high crystallinity based on Raman and XRD analyses. Zinc selenide and sulfide shells with different morphologies were grown on In_1-<i>X</i>Ga_<i>X</i>As QDs by controlling the Zn precursor chemistry. Despite the nominally reduced lattice mismatch in the In_1-<i>X</i>Ga_<i>X</i>As/ZnSe heterostructure, a ZnS shell was found to be a much more effective passivation material: In_1-<i>X</i>Ga_<i>X</i>As/ZnS core-shell QDs show a photoluminescence quantum yield (PL QY) of about 30% versus 11% for ZnSe shells. Based on the analysis of PL decay and transient absorption (TA) dynamics, we surmise that electron trapping is the major reason for efficiency loss, providing a clear heterostructure design principle for realizing efficient NIR-emitting In_1-<i>X</i>Ga_<i>X</i>As QDs.