  We theoretically study the tunnelling current of a single electron transistor
(SET) under optical pumping. It found that holes in the quantum dot(QD) created
by optical pumping lead to new channels for the electrons tunnelling from
emitter to collector. As a consequence, an electron can tunnel through the QD
via additional channels, characterized by the exciton, trion and biexciton
states. The binding energy of exciton complexes can be determined by the
Coulomb oscillatory tunnelling current.
