The surface energy band diagrams and the electron affinity of hydrogen-terminated and oxygen-terminated highly phosphorous-doped single crystal diamond (111) surfaces have been studied by ultraviolet photoelectron spectroscopy, secondary electron spectroscopy, X-ray photoelectron spectroscopy and photoemission electron microspectroscopy. A hydrogen-terminated boron-doped diamond (001) surface was used as a reference of surface energy band diagram. The electron affinity of the H-terminated heavily P-doped diamond was determined to be 0.2 ± 0.15 eV, thus close to zero. The electron affinity of the O-terminated highly P-doped diamond was determined to be 0.0 ± 0.15 eV, thus can be negative. However, the surface energy bands for the two highly P-doped samples were found to have large amounts (3 eV) of upward bending toward surface.

The mechanism of field emission from a highly P-doped diamond (111) surface has been studied by field/photo emission electron micro-spectroscopy. It was found that field emission peaks were located at À3 to À6 eV with respect to the substrate Fermi level (E F ) and that photoemission peaks were located at À1 to þ2 eV with respect to the substrate E F . Comparing this with the knowledge of work function and electron affinity of the sample, the mechanism of field emission has been elucidated. Namely, field emitted electrons are tunnel-emitted from states around the surface E F and there is a large amount of resistive potential drop at the emission site.

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