  Negative Electron Affinity (NEA) activated surfaces are required to extract
highly spin polarized electron beams from GaAs-based photocathodes, but they
suffer extreme sensitivity to poor vacuum conditions that results in rapid
degradation of quantum efficiency. We report on series of unconventional NEA
activations on surfaces of bulk GaAs with Cs, Sb, and O2 using different
methods of oxygen exposure for optimizing photocathode performance. One order
of magnitude improvement in lifetime with respect to the standard Cs-O2
activation is achieved without significant loss on electron spin polarization
and quantum efficiency by codepositing Cs, Sb, and O2. A strained GaAs/GaAsP
superlattice sample activated with the codeposition method demonstrated similar
enhancement in lifetime near the photoemission threshold while maintaining 90%
spin polarization.
