Holes in the Valence Band of Superconducting Boron-Doped Diamond Film Studied by Soft X-ray Absorption and Emission Spectroscopy

Carbon- and boron-2 p states of superconducting and non-superconducting boron-doped diamond (BDD) samples are measured using soft X-ray emission and absorption spectroscopy (XES and XAS) near C- and B-K edges. The electronic structure of B 2 p does not show a marked boron-doping dependence, except that a considerable amount of in-gap state in empty states is observed. In C-K XAS spectra, two peaks H and I are observed around the Fermi level. The H peak is attributed to 2 p state of carbon first-nearest neighboring to the dopant boron atoms (1NN-C), and the I peak to 2 p state of carbon further than 1NN-C from an impurity boron. Incoherent (normal-excitation) XES spectra do not show a large chemical shift by B-doping, but its intensity just below the valence band maximum (VBM) decreases with B-doping. It cannot be interpreted within a simple rigid band model. An elastic peak of I -excited C-K XES spectrum and the width of I -peak of C-K XAS spectrum suggest that impurity state is localized in non-supercond...