  We investigate the spin relaxation and spin dephasing of $n$-type GaAs
quantum wells. We obtain the spin relaxation time $T_1$, the spin dephasing
time $T_2$ and the ensemble spin dephasing time $T_2^{\ast}$ by solving the
full microscopic kinetic spin Bloch equations, and we show that, analogous to
the common sense in an isotropic system for conduction electrons, $T_1$, $T_2$
and $T_2^{\ast}$ are identical due to the short correlation time. The
inhomogeneous broadening induced by the D'yakonov-Perel term is suppressed by
the scattering, especially the Coulomb scattering, in this system.
