GaN(Cs) has some interesting characteristics: high QE in the UV range, better stability and a longer lifetime than GaAs, NEA surface can be achieved only with cesium, Efficient reactivation by simple vacuum bakeout and GaN samples are commercially available. GaN(Cs) photocathodes have been considered by accelerator labs in last years. P-type GaN on sapphire with Au/Ni was used for our first experiment. Only cesium was involved in the activation process. 5 cycles of reactivation were done for the same sample, maximum QE of 5% @ 262 nm was achieved.
R. Xiang, et al., Research Activities on Photocathodes for HZDR SRF Gun, Proceedings of IPAC 2012