  The spin accumulation in an n-GaAs channel produced by spin extraction into a
(Ga,Mn)As contact is measured by cross-sectional imaging of the spin
polarization in GaAs. The spin polarization is observed in a 1 \mum thick
n-GaAs channel with the maximum polarization near the contact edge opposite to
the maximum current density. The one-dimensional model of electron drift and
spin diffusion frequently used cannot explain this observation. It also leads
to incorrect spin lifetimes from Hanle curves with a strong bias and distance
dependence. Numerical simulations based on a two-dimensional drift-diffusion
model, however, reproduce the observed spin distribution quite well and lead to
realistic spin lifetimes.
