  By incorporating the proper boundary conditions, we analytically derive the
impulse response (or "Green's function") of a current-sensing spin detector. We
also compare this result to a Monte-Carlo simulation (which automatically takes
the proper boundary condition into account) and an empirical spin transit time
distribution obtained from experimental spin precession measurements. In the
strong drift-dominated transport regime, this spin current impulse response can
be approximated by multiplying the spin density impulse response by the average
drift velocity. However, in weak drift fields, large modeling errors up to a
factor of 3 in most-probable spin transit time can be incurred unless the full
spin current Green's function is used.
