Electronic structure of hydrogenated diamond: Microscopical insight into surface conductivity

We have correlated the surface conductivity of hydrogen-terminated diamond to the electronic structure in the Fermi region. Significant density of electronic states (DOS) in proximity of the Fermi edge has been measured by photoelectron spectroscopy (PES) on surfaces exposed to air, corresponding to a p-type electric conductive regime, while upon annealing a depletion of the DOS has been achieved, resembling the diamond insulating state. The surface and subsurface electronic structure has been determined, exploiting the different probing depths of PES applied in a photon energy range between 7 and 31 eV. Ab initio density functional calculations including surface charge depletion and band-bending effects favorably compare with electronic states measured by angular-resolved photoelectron spectroscopy. Such states are organized in the energy-momentum space in a twofold structure: one, bulk-derived, band disperses in the Gamma-X direction with an average hole effective mass of (0.43 +/- 0.02)m(0), where m(0) is the bare electron mass; a second flatter band, with an effective mass of (2.2 +/- 0.9)m(0), proves that a hole gas confined in the topmost layers is responsible for the conductivity of the (2 x 1) hydrogen-terminated diamond (100) surface.