The GaN(Cs) has been considered as a photocathode by accelerator labs since last years, because the 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.
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. Starting from 2018 a new GaN cathode system with sample cleaning, activation and analysis function is building at HZDR. More studies will be done in order to explore the possiblity to apply this material in SRF gun.
BMBF-Verbundprojekt 05K2016: HOPE-II
Jana Schaber, The attempt of using GaN as a photocathode in SRF Gun II, presented in the 5th MT Meeting, Jena.
R. Xiang, et al., Research Activities on Photocathodes for HZDR SRF Gun, Proceedings of IPAC 2012