Angle-resolved photoemission studies of Ge(111)-c(2×8), Ge(111)-(1×1)H, Si(111)-(7×7), and Si(100)-(2×1)

Angle-resolved photoemission measurements have been carried out for Ge(111)-c(2×8), Ge(111)-(1×1)H, Si(111)-(7×7), and Si(100)-(2×1) in a normal emission geometry over a wide photon energy range. For Ge(111) and Si(100), dispersive bulk-derived transitions were observed, from which we have determined the bulk valence-band dispersion relations for Ge along the [111] direction and for Si along the [100] direction in the Brillouin zone. The results are compared with the theoretical band dispersions of Chelikowsky and Cohen [Phys. Rev. B 14, 556 (1976)]. For Si(111)-(7×7), the spectra are dominated by nondispersive features which cannot be used for band mapping. The lack of dispersive bulk-transition features for Si(111)-(7×7) is explained in terms of a relatively extended near-surface strain field which renders the electron crystal momentum highly mixed. Several surface-state features on these surfaces were also observed; most of them are visible over a very wide photon energy range and are indeed dispersionless, confirming the previous surface-state assignments.