  In a spin field effect transistor, a magnetic field is inevitably present in
the channel because of the ferromagnetic source and drain contacts. This field
causes random unwanted spin precession when carriers interact with non-magnetic
impurities. The randomized spins lead to a large leakage current when the
transistor is in the ``off''-state, resulting in significant standby power
dissipation. We can counter this effect of the magnetic field by engineering
the Dresselhaus spin-orbit interaction in the channel with a backgate. For
realistic device parameters, a nearly perfect cancellation is possible, which
should result in a low leakage current.
