Negative electron affinity photocathode research and technology

Negative electron affinity (NEA) photocathodes provide greatly increased sensitivity, particularly in the near infrared (λ < 1.0µ). For example, yields of 0.03 electron/photon at 1.06µ (100 times that of conventional photon cathodes) have been achieved in sealed off photomultiplier tubes. In NEA cathodes (usually fabricated from III-V compounds), the vacuum potential is below conduction band minimum (CBM) in the bulk of the material; thus, electrons excited across the bandgap can thermalize to the CBM, diffuse to the surface and escape into vacuum. The development of NEA cathodes and problems and characteristics in practical tubes will be discussed.