  We propose an efficient spin filter including an antidot fabricated on
semiconductor heterostructures with strong spin-orbit interaction. The antidot
creates a tunable potential on two-dimensional electron gas in the
heterostructures, which may be attractive as well as repulsive. Our idea is
based on the enhancement of extrinsic spin Hall effect by resonant scattering
when the attractive potential is properly tuned. Numerical studies for three-
and four-terminal devices indicate that the efficiency of the spin filter can
be more than 50% by tuning the potential to the resonant condition.
