The main advantage of superlattice (SL) structures as spin polarized electron emitters is the ability to provide a large splitting between the heavy hole (HH) and light hole (LH) valence bands (VB) over a large active thickness compared to single strained layers. Two important depolarization mechanisms in these structures are the scattering effects during the transit of the electrons in the active region and the depolarization that takes place in the band bending region (BBR) near the surface. In this paper, we systematically study the effects of the electron mobility and transit time by using an InAlGaAs/GaAs SL with a flat conduction band (CB). Initial results by the SPTU-SLAC collaboration using such structures grown by the Ioffe Institute showed polarization and quantum yield (QE) of 92% and 0.2% respectively. We report measurements using similar structures grown by SVT Associates. The results (polarization up to 90%) are also compared with simulations.