Electron emission from negative affinity semiconductors

Negative electron affinity (NEA) electron emitters are presently being used in every general area requiring electron emitting devices, photocathodes, secondary electron emission dynodes, and cathodes simply for electron sources. NEA emitters are semiconductor devices whose surfaces have been treated so that the bottom of the conduction band in the bulk of the device lies at an energy higher than the vacuum energy. Thus, any electron present in the conduction band within a minority carrier diffusion length of the surface has a reasonable chance of escaping into vacuum with no further application of energy. The performance of the devices can be accurately described by conventional semiconductor theory, and the limitations are reasonably well understood as will be described. The properties of the emitted electron beams are somewhat different from those released from conventional electron emitting surfaces. These differences affect device performance and, in some cases, may lead to devices which otherwise would not be practical. The present state of the art will be described both with respect to commercial devices which are now available and also developments which are likely to result in devices for the near future.