  We investigate a silicon single-electron transistor (SET) in a
metal-oxide-semiconductor (MOS) structure by applying a magnetic field
perpendicular to the sample surface. The quantum dot is defined
electrostatically in a point contact channel and by the potential barriers from
negatively charged interface traps. The magnetic field dependence of the
excitation spectrum is primarily driven by the Zeeman effect. In the
two-electron singlet-triplet (ST) transition, electron-electron Coulomb
interaction plays a significant role. The evolution of Coulomb blockade peaks
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 amplitude spectroscopy allows for the
observation of the spin blockade effect, where the two-electron system forms a
singlet state at low fields, and the spin polarized injection from the lead
reduces the tunneling conductance by a factor of 8. At a higher magnetic field,
due to the ST transition, the spin blockade effect is lifted and the
conductance is fully recovered.
