  The conductance modulations in spin field-effect transistors under finite
bias voltages were studied. It was shown that when a finite bias voltage is
applied between two terminals of a spin field-effect transistor, the spin
precession states of injected spin-polarized electrons in the semiconductor
channel of the device will depend not only the gate-voltage controlled Rashba
spin-orbit coupling but also depend on the bias voltage and, hence, the
conductance modulation in the device due to Rashba spin-orbit coupling may also
depend sensitively on the bias voltage.
