  We show theoretically that a strongly spin-polarized current can be generated
in semiconductors by taking advantage of the ferromagnetic phase of a quantum
dot array (QDA). A Hubbard model with coupling to leads is used to study the
tunneling current of the QDA system as a function of gate voltage. Due to the
weak interdot coupling and strong Coulomb repulsion, it is found that a
ferromagnetic phase exists in QDA within a window of gate voltage. Therefore
QDA can be used as a spin filter to detect and control spin states in quantum
information devices.
