Fine structure in the spectrum of the few-electron ground states of self-assembled quantum dots

Abstract We study the ground states of self-assembled InAs quantum dots with high-resolution capacitance spectroscopy. For samples with a relatively large gate area, and therefore large number of dots, we observe essentially single-electron charging into the lowest-energy states of the dots. A complete picture of the evolution of the ground states with electron occupation and magnetic field is established. For smaller samples, an additional fine structure is seen in the capacitance spectra. Its relative amplitude increases with decreasing gate area of the device. The typical energy spacing between the additional maxima is about 5 meV. It is discussed in terms of mesoscopic fluctuations in the capacitance device. For samples containing very few dots the spectra consist of sharp charging peaks, some of which are separated by the typical energy of the fine structure.