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GaAs-GaAsP and InGaAs-AlGaAs strained-layer superlattice photocathodes are presented as emission sources for highly polarized electron beams. The GaAs-GaAsP cathode achieved a maximum polarization of 92(±6)% with a quantum efficiency of 0.5%, while the InGaAs-AlGaAs cathode provides a higher quantum efficiency (0.7%) but a lower polarization (77(±5)%). Criteria for achieving high polarization using superlattice (SL) photocathodes are discussed based on experimental spin-resolved quantum efficiency spectra.