Single-Electron Spectroscopy of Quantum Dots using Vertically Self-aligned Electrode Structure.

We demonstrate single-electron tunneling spectroscopy of individual quantum dots using new vertical electrode structure, where the source and drain electrodes are vertically self-aligned and separated by a thin dielectric spacer. A quantum dot placed on the periphery between the source and the drain electrodes forms a double barrier tunnel junction, allowing for single-electron spectroscopy measurements. CMOS compatible fabrication allows many quantum dot units to be fabricated in parallel processing. This technique not only provides an accurate electronic structure of a ``single'' quantum dot, but such measurement can be made for many of individual quantum dot units fabricated in a single batch process. Thus, this simple procedure provides accurate energy level measurement of ``single'' quantum dots over the entire quantum dot population. The band gap (E$_{g})$, charging energy (E$_{c})$ and energy level spacing ($\Delta $E) were measured directly from the current-voltage and differential conductance spectra for colloidal CdSe quantum dots ($\sim $6.5nm). The band gap was measured to be E$_{g} \quad \sim $1.75-1.85eV, charging energy E$_{c} \quad \sim $60meV and the `s' to `p' level separation ($\Delta $E ) was measured to be $\sim $60-100meV. (Supported by NSF CAREER (ECS-0449958), ONR (N00014-05-1-0030), and THECB ARP (003656-0014-2006)).