Element-Selective Observation of Electronic Structure Transition between Semiconducting and Metallic States in Boron-Doped Diamond Using Soft X-ray Emission and Absorption Spectroscopy

Abstract

The electronic structure transition between the semiconducting and metallic states in boron (B)-doped diamonds was element-selectively observed by soft X-ray emission and absorption spectroscopy using synchrotron radiation. For lightly B-doped diamonds, the B 2 p-density of states (DOS) in the valence band was enhanced with a steep-edge feature near the Fermi level, and localized acceptor levels, which are characteristic of semiconductors, were clearly observed both in B 2 p- and C 2 p-DOS in the conduction bands. For heavily B-doped diamonds, the localized acceptor levels developed into extended energy levels and the new energy levels generated formed an extended conduction band structure that overlapped with the valence band. Thus, the metallic energy band structure is actually formed by heavy boron doping. These valence and conduction band structures observed by soft X-ray emission and absorption spectroscopy accounted for the electrical properties of B-doped diamonds.