  We investigate the spin dynamics and relaxation in remotely-doped two
dimensional electron systems where the dopants lead to random fluctuations of
the Rashba spin-orbit coupling. Due to the resulting random spin precession,
the spin relaxation time is limited by the strength and spatial scale of the
random contribution to the spin-orbit coupling. We concentrate on the role of
the randomness for two systems where the direction of the spin-orbit field does
not depend on the electron momentum: the spin field-effect transistor with
balanced Rashba and Dresselhaus couplings and the (011) quantum well. Both of
these systems are considered as promising for the spintronics applications
because of the suppression of the Dyakonov-Perel' mechanism there makes the
realization of a spin field effect transistor in the diffusive regime possible.
We demonstrate that the spin relaxation through the randomness of spin-orbit
coupling imposes important physical limitations on the operational properties
of these devices.
