Recent developments of highly efficient electron emissions from chemical-vapor-deposited (CVD) single-crystalline diamond under high fields of ≈ 106 to ≈ 107 V/cm have been described in relation to those of surface structure analysis using a scanning tunneling microscope, photoemission threshold-energy measurements and Monte Carlo (MC) simulations of carrier transports under high electric fields. Photoemission data indicate that the electron affinity of as-grown CVD diamond (100) changes from negative to positive values with increasing oxygen coverages, being well reproduced by the Topping model. From MC calculations, it has been verified that valence electrons of diamond can be excited to the conduction band through impact ionization events under the high fields concerned. Very high (current) efficiencies of ≈ 100% have been observed for a diode-type electron emitter having a buried electrode layer, an insulating diamond layer and a p-type diamond emission surface with a negative electron affinity. A model has been proposed for the high emission efficiency attained, based upon the impact carrier excitation process.
