Long‐Range Transport in an Assembly of ZnO Quantum Dots: The Effects of Quantum Confinement, Coulomb Repulsion and Structural Disorder

Publisher Website
Google Scholar
Abstract
We have studied the storage and long‐range transport of electrons in a porous assembly of weakly coupled ZnO quantum dots permeated with an aqueous and a propylene carbonate electrolyte solution. The number of electrons per ZnO quantum dot is controlled by the electrochemical potential of the assembly; the charge of the electrons is compensated by ions present in the pores. We show with optical and electrical measurements that the injected electrons occupy the S, P, and D type conduction electron levels of the quantum dots; electron storage in surface states is not important. With this method of three‐dimensional charge compensation, up to ten electrons per quantum‐dot can be stored if the assembly is permeated with an aqueous electrolyte. The screening of the electron charge is less effective in the case of an assembly permeated with a propylene carbonate electrolyte solution. Long‐range electron transport is studied with a transistor set‐up. In the case of ZnO assemblies permeated with an aqueous electrolyte, two quantum regimes are observed corresponding to multiple tunnelling between the S orbitals (at a low occupation) and P orbitals (at a higher occupation). In a ZnO quantum‐dot assembly permeated with a propylene carbonate electrolyte solution, there is a strong overlap between these two regimes.