Aging studies on hybrid photon detectors with Cs activated monocrystalline photocathodes

Hybrid photon detectors are one of the preferred candidates for a light detector with high quantum efficiency in the visible range and single photoelectron resolution. To reach a high sensitivity Cs-activated monocrystalline GaAs or GaAsP photocathodes are used. Prototypes of such HPDs have shown a peak QE up to 45% at 500 nm, but no extensive studies on its aging properties have been performed up to now. Ion feedback effects and instabilities on the activation layer will be conceptually studied as the most important aging factors.