Abstract
Photocathodes with (110) cleave plane are shown to be the least susceptible to ion damage. The observed susceptibility is explained by enhanced ion channeling.
Highlights
Direct current high voltage photoemission guns with GaAs photocathodes are used to generate spin-polarized electron beams for nuclear and particle physics research [1]
Photogun experts speculate that ions strike the photocathode surface sputtering away the chemicals used to create a negative electron affinity (NEA) condition, or they become implanted within the photocathode material knocking out atoms from the crystal structure and altering the energy band structure, or they serve as interstitial defects that reduce the electron diffusion length
Implantation of the photocathode with either low or high energy hydrogen ions served to reduce photocathode QE, but the QE degradation caused by 100 V hydrogen ions was modest and QE could be recovered following sample heating
Summary
Direct current high voltage photoemission guns with GaAs photocathodes are used to generate spin-polarized electron beams for nuclear and particle physics research [1]. We explored the sensitivity of bulk GaAs photocathodes with (100), (110) and (111A) surface cleave planes to ion bombardment at hydrogen-ion energies of 100 and 10 000 V. Laser light at 532 nm will be absorbed within 1300–1480 Å of the surface [19,20,21] and we note the diffusion length of electrons in GaAs is of the order 1000 Å [22,23] Because these dimensions are comparable to the distance scales described in Fig. 3 for implantation and knock-out vacancies, we hoped that our QE measurements would be sensitive to different ill effects that might result from low and high energy ions at 100 and 10 000 V
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