Because of the high Q.E. in visible light range and the best performance as a polarized electron source, GaAs photocathodes are used worldwide in DC photoinjectors for large accelerator facilities. A project to apply GaAs in the Rossendorf SRF gun has been started. GaAs(Cs, O) is very demanding, for instance an ultrahigh vacuum of 10-11 mbar is required. For this reason, a new preparation chamber and a new transfer system are under development. The first GaAs(Cs,O) cathode will be produced in 2014.
R. Xiang, et al., Polarized Sources, Targets & Polarimetry, published by World Scientific, p249
R. Xiang, et al., Research Activities on Photocathodes for HZDR SRF Gun. Proceedings of IPAC 2012