A test system for optimizing quantum efficiency and dark lifetime of GaAs photocathodes

Gallium-arsenide-based photocathodes are used for a variety of applications, including electron-beam production for particle accelerators. An ultra-high vacuum teststand has been developed for cleaning and preparation of photocathodes. First studies using the apparatus were carried out investigating quantum efficiency and vacuum (dark) lifetimes of GaAs photcathodes that were prepared using different procedures involving Cs, Li, and O-2. While the two-stage activation procedure with Cs and O-2 yielded the highest quantum efficiency of up to (25.9 +/- 1.3) % at wavelength 405 nm, the vacuum lifetime of cathodes activated with Cs, Li, and O-2 using a two-stage process exceeded those obtained in single-stage process by more than a factor of three.