Energy- and spin-resolved photoemission from activated GaAs(100)

The energy- and spin-resolved photoemission from (Cs,O)-activated GaAs(100) surfaces, excited with circularly polarized light hv= 1.5 eV is investigated for different preparation states of the surface. In the case of a NEA surface the energy width of the photoemission increases only slightly at high photocurrents (up to 85 (microA). Permanent cesiation prolongs the useful lifetime considerably without enlarging the energy width. At the beginning of the reactivation of an aged photocathode with a low quantum efficiency an energy distribution with two separated peaks with different polarization is observed. Possible emission processes for the two peaks are discussed.