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 5 nm 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 45 nm long SET shows 2-1-2-1 filling behavior while a 38 nm long SET exhibits 1-2-2-1 filling. These filling behaviors match with the calculated degeneracies of nanowires with different confinement strengths.