Abstract
We have measured k-resolved inverse-photoemission spectra of the Ge(111)2×1 and Si(111)2×1 surfaces. The main spectral features are well described in terms of direct transitions to the three lowest conduction bands along ΓL and a transition to a surface resonance near the conduction-band minimum via a surface umklapp process. An extra feature reflects a maximum in the density of empty states. Several critical points are determined, e.g., for Ge, at 0.7 eV, at 4.2 eV, and at 7.9 eV and a higher L point at 11 eV, and for Si, at 2.4 eV and at 4.15 eV above the valence-band maximum. By comparing our inverse-photoemission results with those from photoemission and optical spectroscopy we find that the transition could be lowered by the electron-hole interaction by up to 0.15 eV for Ge and 0.5 eV for Si. A comparison with first-principles and empirical band calculations is made.
- Received 21 August 1985
DOI:https://doi.org/10.1103/PhysRevB.33.2607
©1986 American Physical Society