  The role of the relaxation due to the impurity scattering and/or the contacts
to leads/electrodes are studied for the spin Hall effect (SHE). Relaxation is
essential to attain the steady state and also to the spin accumulation, but has
been considered to be harmful for the intrinsic SHE (ISHE). These issues are
examined quantitatively on two types of 2D models, i.e., (a) Rashba model for
$n$-type GaAs, and (b) Luttinger model for $p$-type GaAs. It is found that ISHE
is robust against the realistic strength of the disorder producing the
observable amount of the spin accumulation. Especially in model (b) the spin
current and the accumulation are an order of magnitude larger than those in
model (a). Experimental observations are discussed quantitatively from these
results.
