Electron spin blockade and singlet-triplet transition in a silicon single electron transistor

We investigate a silicon single electron transistor in a metal-oxide-semiconductor structure by applying a magnetic field perpendicular to the sample surface. The quantum dot is defined electrostatically in a point-contact channel and by potential barriers probably from negatively charged interface traps. The magnetic field dependence of the excitation spectrum mostly can be attributed to the Zeeman effect. In the two-electron singlet-triplet (ST) transition, electron-electron Coulomb interaction plays a significant role. The evolution of Coulomb blockade peak positions with magnetic field B is also owing to the Zeeman splitting with no obvious orbital effect up to 9 T. The filling pattern shows an alternate spin-up-spin-down sequence. The observed amplitude spectrum can be explained by the spin-blockade effect. When the two-electron system forms a singlet state at low magnetic fields, and the injection current from the lead becomes spin-down polarized, the tunneling conductance is reduced by a factor of 8. At higher fields, due to the ST transition, the spin-blockade effect is lifted and the conductance is fully recovered.