NEA GaAs photocathode for electron source: From growth, cleaning, activation to performance

Benefitting from excellent QE and high polarization, GaAs-based photocathode becomes the most promising candidate for electron source and has made rapid progress in the past 20 years. In this paper, growth, cleaning, and activation are reviewed in sequence, and effects of different parameters on QE and polarization are explored. The QE of GaAs-based photocathode is mainly distributed in the band range of 350-932 nm, and the maximum can reach 49.45 %. QE converges higher as cleaning temperature increases, illustrating that higher annealing temperature can considerably elevate the possibility of obtaining a high QE even if impurities can be eliminated at lower temperature. The optimal activation time for Cs/O activation ranges from 50 to 90 min, and the optimal Cs/O alternations ranges from 7 to 11 times. The operating wavelength of polarized photocathode is above 680 nm while polarization of most superlattice photocathodes can exceed 80 % with QE lower than 1 %. Moreover, an increase in QE leads to a significant decrease in polarization for one superlattice photocathode, indicating that high QE and high polarization cannot be simultaneously achieved. It is hoped that this review will draw more attention to GaAs-based photocathode and promote understanding and application of GaAs-based photocathode.