A photocathode electron source using p-type GaN and p-type InGaN semiconductors with a negative electron affinity
(NEA) surface has been studied for its ability to maintain an extended NEA state. The key technology of NEA
photocathodes is the formation of electric dipoles by atoms on the surface, which makes it possible for photo excited
electrons in the conduction band minimum to escape into the vacuum. This means that in order to keep the electron
energy spread as small as possible, the excitation photon energy should be tuned to the band gap energy. However, the
NEA surface is damaged by the adsorption of residual gas and the back-bombardment of ionized residual gas by
photoelectrons. The p-type GaN and InGaN semiconductors were measured a lifetime of quantum yield of excitation
energy corresponding to the band gap energy in comparison to the p-type GaAs as the conventional NEA photocathode.
Lifetime of NEA-photocathodes using the GaN and InGaN were 21 times and 7.7 times longer respectively than that
using the GaAs.