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 (28), Ge (111) - (11) H, Si (111) - (77), and Si (100) - (21) 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) - (77), the spectra are dominated by nondispersive features which cannot be used for band mapping. The lack of dispersive bulk-transition features for Si (111) - (77) 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.