Photoemission and Related Properties of the Alkali-Antimonides

Abstract

The photoemissive process in the semiconducting alkali‐antimonides is examined and values are given for the band gaps and electron affinities. The high photoelectric efficiencies of these materials are attributed to the ability of the excited electrons to traverse relatively large distances (250 A) without overwhelming energy losses, rather than to negligibly small electron affinities. The efficiency is found to be strongly dependent on the percentage of the electrons which are excited into states above the vacuum level. The properties of these materials depend to a large extent on the crystal structure. Cs₃Sb and Na₂KSb have a cubic structure, are p type, and seem to have a relatively simple valence band structure. K₃Sb and Na₃Sb have hexagonal crystal structures, are n type, and seem to have a relatively complex valence band structure. The evidence for an effect of band bending on the photoemission is considered.