Observation of three-dimensional shell filling in cylindrical silicon nanowire single electron transistors

The authors have measured addition energy spectra from gate-all-around twin silicon nanowire single electron transistors (SETs) with the radius of 5nm and with circular cross sections. Nonmonotonically varying addition energies are observed and the authors interpret them as shell fillings of silicon nanowire quantum dots with three-dimensional harmonic confinement potentials. A 45nm long SET shows 2-1-2-1 filling behavior while a 38nm long SET exhibits 1-2-2-1 filling. These filling behaviors match with the calculated degeneracies of nanowires with different confinement strengths.