Abstract
Bulk and surface sensitive x-ray spectroscopic techniques are applied in tandem to show that the valence band edge for is found significantly closer to the bottom of the conduction band than expected on the basis of the widely quoted bulk band gap of 3.75 eV. First-principles theory shows that the upper valence bands of exhibit a small dispersion and the conduction band minimum is positioned at . However, direct optical transitions give a minimal dipole intensity until 0.8 eV below the valence band maximum. The results set an upper limit on the fundamental band gap of 2.9 eV.
- Received 5 November 2007
DOI:https://doi.org/10.1103/PhysRevLett.100.167402
©2008 American Physical Society