Lifetime Measurements of GaAs photocathodes at the Upgraded Injector Test Facility at Jefferson Lab

Photo-cathodes based on GaAs can be used in photo-electron sources to supply spin-polarized, high-current electron beams for various applications. An activation, adding a thin surface layer, is needed to achieve negative electron affinity (NEA) for such cathodes. Typically, Cs is used in combination with an oxidant. Previous studies have suggested that the addition of Li to this process can increase the quantum efficiency $\eta$ of the cathode as well as the lifetime $\tau$ of the cathode surface layer, both crucial parameters for photo-electron source operation. Charge lifetime studies of bulk GaAs photo-cathodes activated with Cs, NF$_3$, and Li have been conducted using the photo-electron gun of the Upgraded Injector Test Facility (UITF) at the Thomas Jefferson National Accelerator Facility (JLab), extracting beam currents of up to 100 µA. Evidence for significant charge lifetime enhancement with Li in the activation process is found.