Abstract
Cold field electron emission (CFE) is a statistical electron emission regime where the emitted current is generated by the escape of electrons by Fowler-Nordheim (FN) tunnelling from states close in energy to the emitter's Fermi level. Particularly over the last ten years or so, there has been much interest in developing electron sources based on CFE from relatively large substrate areas that support many individual emitters or emission sites. In this paper, the use of the concept of "area efficiency of emission" when dealing with equations describing field emission from large-area electron sources is presented.