SINGLE-ELECTRON CAPACITANCE SPECTROSCOPY OF A FEW ELECTRON BOX

This paper presents a technique which permits a quantitative spectroscopy of discrete quantum levels in structures containing as few as one electron. The ground state energy in a quantum dot can-be measured for an arbitrary number of electrons and followed as a function of magnetic field. The method involves monitoring the capacitance signal resulting from the tunneling of single electrons. In a microscopic capacitor fabricated in GaAs we study the confined states of a single 1 mum disk to which electrons can tunnel from a nearby metallic layer. Charge transfer occurs only for bias voltages at which a quantum level is resonant with the Fermi energy of the metallic layer. This creates a sequence of distinct capacitance peaks whose bias positions can be directly converted to an energy scale to determine the electronic spectrum of the confined structure. The evolution of the spectrum in magnetic field allows deduction of the nature of the bound states.