Photocathode performance measurements for the SLC polarized electron gun

A low-voltage test system is used to qualify various III-V semiconductor materials as photocathodes for the SLC. The system features a load lock to introduce samples, high pumping speed, a sensitive residual gas analyzer, and an infrared temperature detector. Heat cleaning, cesiation, and oxidation procedures have been studied to optimize cathode activation for achieving an optimum NEA surface. VGF GaAs, MBE-grown AlGaAs, MBE GaAs layered on AlGaAs, and MOCVD GaAsP cathodes with different active layer thicknesses and doping concentrations have been tested for quantum efficiency and lifetime. New higher-polarization strained-layer GaAs and GaAsP photocathodes have also been tested. Results and operational experience are discussed.<
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