The valence bands of the unreconstructed H-Si(111)-1×1 are investigated using angle-resolved ultraviolet photoelectron spectroscopy. The high quality of the surface and the absence of reconstruction allow us to observe bulk bands comparable to theoretical calculations. The asymmetric dispersion of the valence bands along the ${\overline{M}}^{\prime }\overline{\Gamma }\overline{M}$ direction of the surface Brillouin zone confirms the asymmetry observed for the conduction bands. Such an asymmetry, stemming from the fact that the family of ($11\overline{2}$) planes are not mirror planes in the bulk of Si, provides a supplementary means of disentangling bulk states from surface states.

• Received 6 March 1996

DOI:https://doi.org/10.1103/PhysRevB.54.17654