Secondary photoelectron emission experiments on p-, intrinsic, and n-type diamond

Total photoyield spectroscopy (TPYS) is applied to characterize the surface electronic properties of hydrogen-terminated and reconstructed diamond. All samples (n-, p-type doped, undoped) show an onset of electron emission at around 4.4 eV. Obviously, direct excitation of valence-band electrons into the vacuum, which is on hydrogen-terminated diamond 1.1 eV below the conduction band minimum, takes place in the close vicinity of the surface. This photoexcitation on hydrogen-terminated diamond with negative electron affinity is discussed applying different annealing treatments in UHV on diamond. Hydrogen evaporation results in a shift of the TPY spectrum. Taking into account the energy dependent properties of TPY spectra, an electron affinity of + 1.17 ± 0.05 eV is calculated for the clean (001) diamond surface. After a re-hydrogenation of the surface the properties recover completely, which results in a comparable spectrum as before hydrogen evaporation. Applying annealing treatments, where only a small fraction of hydrogen evaporates, results in a shift of the sub-band TPY onsets towards high energies. An indication that with decreasing hydrogen-termination of the diamond surface a decrease of negative electron affinity is detected. These data are discussed in detail taking into account a new photoexcitation mechanism.