Observation of charge transport through CdSe/ZnS quantum dots in a single-electron transistor structure

We fabricated single-electron transistors (SETs) having CdSe/ZnS core-shell-type quantum dots (CdSe/ZnS-QDs) as a Coulomb island using a wet chemistry technique. The CdSe/ZnS-QDs were deposited onto Au electrodes with or without the assistance of a self-assembled monolayer of octane(di)thiols. The CdSe/ZnS-QDs were adsorbed onto the Au electrodes even without the interlayer of thiol molecules depending on the concentration of the CdSe/ZnS-QD solution. The electron-transport characteristics through the CdSe/ZnS-QDs were examined in an SET structure at 13 K. Coulomb blockade behavior with typical gate voltage dependence was clearly observed. The estimated charge addition energies of a CdSe/ZnS-QD ranged from 70 to 280 meV. Moreover, additional structures, including negative differential conductance, appeared in the stability diagram in the source-drain bias region beyond 100 mV; these structures are specific to single-charge transport through the discrete energy levels in the Coulomb island.