Photocathode electron beam sources using GaN and InGaN with NEA surface

Abstract

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.

Observation of relaxation time of surface charge limit for InGaN photocathodes with negative electron affinity

“…14) Damaging the surface increases the affinity of the surface to a positive value and the tunneling probability significantly decreases. Machuca and co-workers, 15,16) and our previous studies 17,18) have revealed that the NEA states of wide-gap semiconductors such as GaN and InGaN are more robust than those of GaAs.…”

Perspectives on Designer Photocathodes for X-ray Free-Electron Lasers: Influencing Emission Properties with Heterostructures and Nanoengineered Electronic States

“…In some cases, QEs of well over 20% have been reported for NEA treated GaN-based photocathodes under UV illumination. Various reports suggest that certain properties of GaN-based semiconductors can be tailored to enhance photoemission including band gap engineering 122,123 , doping 124,125 , utilizing inherent polarization fields 124 , nanowire structures 126 , quantum well structures 122,123 , and heterojunction schemes 119,127 . Some of these reports show promising results for limited application areas, but systematic investigations are lacking and there is limited information regarding photocathode lifetimes and no information on emittance measurements.…”

Novel electron beam technology using InGaN photocathode for high-throughput scanning electron microscope imaging

“…11 However, because the NEA surface of a GaAs photocathode is sensitive to surface damage, the vacuum pressure must be lower than 10 −9 Pa, making such photocathode difficult to be used in industrial equipment operating at a vacuum pressure higher than 10 −9 Pa. On the other hand, wide-gap semiconductors, such as GaN and InGaN, are attractive candidates for industrial applications because of their high stability and more than 10 times longer QE lifetime than GaAs. 12,13 An InGaN is suitable for industrial use because of the availability of a visible laser as an excitation light source and transmission-type structure. 14 The following are the three goals of this study.…”