Energy level tunneling spectroscopy and single electron charging in individual CdSe quantum dots

We directly show the evolution of the electronic structure of semiconductor quantum dots (QDs) with QD size in the strong confinement regime by employing low-temperature tunneling current-voltage spectroscopy to individual electrodeposited CdSe QDs. From the spectra we measure the values of E-g, map discrete energy levels in both valence and conduction "bands," and show the occurrence of single-electron tunneling effects for isolated QDs of different sizes (2, 3, and 4.5 nm diameter). Since tunneling is not limited by optical selection rules, we are able to directly measure energy level spacings not necessarily accessible by optical spectroscopy. Our spectra demonstrate the interplay between charging and energy level spacing, resulting in a rich and controllable structure that forms a basis for QD nanoelectronic devices. (C) 1999 American Institute of Physics. [S0003-6951(99)02138-5].