Electron emission properties of negative electron affinity diamond surfaces

Study of the electron emission properties of negative electron affinity diamond surfaces for near band-gap excitation photon energies finds exciton (bound electron-hole pairs) dissociation at the surface to play an important role in the observed total electron yield. Photoelectron emission measurements from the as-polished, negative electron affinity (NEA) (111)1x1:H diamond surface demonstrate exciton break-up at the surface as the dominant component of photoelectron emission. Dependence of photoelectron emission characteristics upon excitation photon energy suggests the thermalization of the carriers via Fan phonon-cascade mechanism. Modification of this surface to exhibit additional downward band-bending (re-hydrogenated (111)1x1:H diamond surface) significantly enhances the electron emission of conduction band minimum electrons (unbound electron-hole pairs). Photoelectron emission experiments from the TiO-(111)2x1 diamond interface, finds negative electron affinity and similar band-bending with the re-hydrogenated (111) diamond surface. Consistent with our claim that the conduction band minimum electron emission is enhanced in the presence of downward band-bending, we find that a significant part of the observed emission from the TiO-diamond interface is due to conduction band minimum electrons. Experiments on the negative electron affinity (100) diamond surface yield similar results confirming our exciton-derived emission model for photoelectric yield.