PERIODIC AND APERIODIC BUNCHING IN THE ADDITION SPECTRA OF QUANTUM DOTS

We study electron addition spectra of quantum dots in a broad range of electron occupancies starting from the first electron. Spectra for do ts containing <200 electrons reveal a surprising feature. Electron add itions are not evenly spaced in gate voltage. Rather, they group into bunches. With an increasing number of electrons the bunching evolves f rom occurring randomly to periodically at about every 5th electron. Th e periodicity of the bunching and features in electron tunneling rates suggest that the bunching is associated with electron additions into spatially distinct regions within the dots.