Publikationsrepositorium - Helmholtz-Zentrum Dresden-Rossendorf

SRF injectors need materials which can promise high quantum efficiency, long lifetime and good vacuum stability, fast response time and low thermal emittance.
It is assumed that GaN, like GaAs, as a novel electron source for particle accelerators shows an enormous potential.
P-type GaN on different substrate material is activated by a thin layer of caesium and illuminated at the same time by ultra-violet (UV) light. As a consequence of a NEA surface and photoeffect, the generated photoelectrons enter into vacuum and are collected by an anode. The resulting photocurrent is detected during the whole activation process and stopped when a maximum photocurrent is reached. Quantum efficiency (QE) can be calculated from the photocurrent. Its decay is tracked in the following days after activation. It is also studied to re-activate the sample again by using thermal heat treatment and caesium Deposition once more.
High 11.5% QE can be provided from GaN:Cs on sapphire substrate at the moment. After 600 h of lifetime this photocathode shows still 1.4% QE.
Besides the outstanding experimental results so far further investigations are still required.