Comparative study of GaN and GaAs photocathodes

Taking GaAs and GaN as representation, negative electron affinity (NEA) photocathode has many virtues, such as high quantum efficiency, low dark current, concentrated electrons energy distribution and angle distribution, adjustive long-wave threshold, great potential to extend the long-wave spectral response waveband. Therefore it plays more and more important effect in high performance image intensifiers and polarized electron sources. GaN NEA photocathode and GaAs NEA photocathode are very similar because they all belong to III-V compound. But, GaN photocathode and GaAs photocathode have many difference in such aspects as preparation process, activation manners, stability and application field etc. In this paper, using the multi-information measurement and evaluation system of photocathode, the preparation processes of native reflection-mode GaN photocathode and GaAs photocathode are studied. The different activation manners of GaN photocathode and GaAs photocathode are compared and analyzed. The spectral response and stability of the two kind of photocathode are compared also. The experiments indicate: the atomically clean degree of NEA photocathode surface and the structure of activation layer are the main factors that influence photocathode sensitivity and stability after activation. GaN photocathode and GaAs photocathode have good NEA property and large quantum yield. Compare with GaAs photocathode, GaN photocathode has high stability, and the decay of the quantum yield is comparatively slow.