  We develop the microscopic theory of electron spin dephasing in (110)-grown
quantum wells where the electron scattering time is comparable to or exceeds
the period of spin precession in the effective magnetic field caused by
spin-orbit coupling. Structures with homogeneous and fluctuating Rashba field,
which triggers the dephasing of electron spins aligned along the growth
direction, are analyzed. We show that the Dresselhaus field, which is always
present in zinc-blende-type quantum wells, suppresses the spin dephasing
enabling very long spin lifetime of conduction electrons. The dependence of the
spin lifetime on the electron mobility is found to be nonmonotonic reaching the
minimum in structures where the scattering time is comparable to the period of
spin precession in the effective magnetic field.
