Enhanced Multiexciton Emission Property in Gradient Alloy Core/Shell CdZnSeS/ZnS Quantum Dots: Balance between Surface Passivation and Strain-Induced Lattice Defect

The effect of surface/interface defects on multiexciton recombination is studied with CdZnSeS/ZnS alloy core/ shell quantum dots (QDs) with different shell thicknesses. Through pump-power-related time-resolved photoluminescence/ amplified-spontaneous-emission (ASE) spectra and statistical analysis of single-dot fluorescence, it is indicated that with the epitaxial growth of the ZnS shell, the multiexciton property of the QDs can be improved due to surface passivation, but with further shell growth, interface defects caused by stress accumulation will result in deterioration. The QDs with three monolayers ZnS shell show the best performance with a biexciton quantum yield of 11.6%, biexciton lifetime of similar to 360 ps, and ASE threshold of only 118 mu J cm(-2), with which a vertical cavity surface-emitting laser is fabricated. Our experimental results highlight the importance of surface/interfacial defects to the application of QDs on laser devices.

Automated summary

The penetration growth of a ZnS shell on CdZnSeS/ZnS alloy core/shell quantum dots improves the multiexciton property of the dots, but further shell growth can lead to interface defects deterioration. Quantum dots with a three-monolayer ZnS shell demonstrate the best performance.