Photoemission study of electronic structure evolution across the metal–insulator transition of heavily B-doped diamond Original Research Article

We studied the electronic structure evolution of heavily B-doped diamond films across the metal–insulator transition (MIT) using ultraviolet photoemission spectroscopy (UPS). From high-temperature UPS, through which electronic states near the Fermi level (EF) up to ∼5kBT can be observed (kB is the Boltzmann constant and T the temperature), we observed the carrier concentration dependence of spectral shapes near EF. Using another carrier concentration dependent UPS, we found that the change in energy position of sp-band of the diamond valence band, which corresponds to the shift of EF, can be explained by the degenerate semiconductor model, indicating that the diamond valence band is responsible for the metallic states for samples with concentrations above MIT. We discuss a possible electronic structure evolution across MIT.