Caesium deposition on GaN to obtain a photocathode for particle accelerator
Caesium deposition on GaN to obtain a photocathode for particle accelerator
Schaber, J.; Xiang, R.; Teichert, J.; Arnold, A.; Ryzhov, A.; Murcek, P.; Zwartek, P.; Ma, S.
Abstract
Negative electron affinity (NEA) GaAs- and GaN-based photocathodes are used in modern night vison detectors and light emitting diodes1. GaAs semiconductors are already used as electron sources in particle accelerators and well- studied2. Like GaAs, GaN belongs to the
III-V semiconductor group with similar properties. It is assumed that GaN, like GaAs, shows enormous potential as a novel electron source for particle accelerators.
P-type GaN on different substrate material (sapphire, silicon, copper or SiC) is activated by a thin layer of caesium and illuminated by ultra-violet (UV) light at the same time. As a consequence of negative electron affinity (NEA) and photoeffect, the generated photoelectrons enter into vacuum and are collected by a copper ring anode. The resulting photocurrent is detected during the whole activation process and stopped when a maximum photocurrent is reached.
The GaN is chemical cleaned and transferred into a UHV chamber where it undergoes a thermal heat treatment at 250°C for 20 min using a halogen lamp. The aim of the thermal treatment is to remove residual adsorbed gas molecules from the sample surface.
Afterwards when the sample is back at room temperature, the thermal-cleaned GaN is activated with a thin layer of caesium. The photocurrent and the QE is observed in the following days until the QE vanishes. Then it is tested to re-activate the cathode again, meaning to thermal clean it again and to activate it with caesium once more.
By a comparison of differences in substrate material, chemical pre-cleaning, thermal heat treatment and activation parameters (e.g. caesium-flux), the photocurrent, quantum efficiency and the re-activation of the photocathode is studied. Additionally the GaN samples are examined by AFM, SEM and EDX.
From the experimental results obtained so far, it appears that GaN:Cs could be used as a photocathode in particle accelerators, but further investigations are still required and needed.
Keywords: gallium nitride; photocathode; caesium deposition; SRF Gun
Beteiligte Forschungsanlagen
- Strahlungsquelle ELBE DOI: 10.17815/jlsrf-2-58
Verknüpfte Publikationen
- DOI: 10.17815/jlsrf-2-58 is cited by this (Id 32929) publication
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Poster
(Online Präsentation)
DPG-Frühjahrstagung des Fachverbandes Oberflächenphysik, 01.-04.03.2021, Hannover, Deutschland
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