Boosting the Photoluminescence Efficiency of InAs Nanocrystals Synthesized with Aminoarsine via a ZnSe Thick-Shell Overgrowth

InAs-based nanocrystals can enable restriction of hazardous substances (RoHS) compliant optoelectronic devices, but their photoluminescence efficiency needs improvement. We report an optimized synthesis of InAs@ZnSe core@shell nanocrystals allowing to tune the ZnSe shell thickness up to seven mono-layers (ML) and to boost the emission, reaching a quantum yield of & AP;70% at & AP;900 nm. It is demonstrated that a high quantum yield can be attained when the shell thickness is at least & AP;3ML. Notably, the photoluminescence lifetimeshows only a minor variation as a function of shell thickness, whereas the Auger recombination time (a limiting aspect in technological applications when fast) slows down from 11 to 38 ps when increasing the shell thickness from 1.5 to 7MLs. Chemical and structural analyses evidence that InAs@ZnSe nanocrystals do not exhibit any strain at the core-shell interface, likely due to the formation of an In-Zn-Se interlayer. This is supported by atomistic modeling, which indicates the interlayer as being composed of In, Zn, Se and cation vacancies, alike to the In2ZnSe4 crystal structure. The simulations reveal an electronic structure consistent with that of type-I heterostructures, in which localized trap states can be passivated by a thick shell (>3ML) and excitons are confined in the core.

Automated summary

We have successfully synthesized InAs@ZnSe core-shell nanocrystals with tunable shell thickness up to seven mono-layers (ML) and enhanced photoluminescence efficiency, achieving a quantum yield of over 70% at around 900nm. The experiments demonstrate that a high quantum yield can be obtained when the shell thickness is at least 3ML. Chemical and structural analyses reveal the absence of strain at the core-shell interface, likely due to the formation of an In-Zn-Se interlayer. Atomistic modeling confirms the existence of an interlayer composed of In, Zn, Se, and cation vacancies, similar to the structure of In2ZnSe4. The simulations also show a type-I electronic structure, where localized trap states can be passivated by a thick shell (>3ML) and excitons are confined in the core.