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In this paper we present a detailed photoemission study of the K/Si(111)7[times]7 and K/Si(111)([radical]3 [times] [radical]3 )[ital R]30[degree]-B interfaces. Angle-resolved valence-band spectroscopy reveals the presence of an almost dispersionless interface state [ital below] [ital E][sub [ital F]]. Both interfaces are clearly nonmetallic at room-temperature saturation coverage. We critically address the issues of charge transfer and Fermi-level pinning by a detailed analysis of the K 3[ital p] and Si 2[ital p] core-level spectra. We conclude that, up to saturation coverage, correlation effects determine the electronic properties of these interfaces. Metallization occurs during the development of the second layer at cryogenic temperatures.

We present a structural model for the metal-induced Si(111)3[times]1 reconstruction. Fivefold Si rings form one-dimensional [pi]-bonded chains along [l angle]1[bar 1]0[r angle]. These chains are separated by empty channels that can accommodate 1/3 monolayer of metal atoms. We propose that the [pi]-bonded chains undergo a strong disturbance resulting in the formation of alternating dimers consistent with published scanning tunneling microscope images [K. J. Wan [ital et] [ital al]., Phys. Rev. B 46, 13 635 (1992)]. Unlike previous models, this model accounts for most experimental observations, including a large band gap and chemical passivation.

Owing to the strong dependence of the resistivity on the dopant concentration, nonuniformity across the thickness of a sample leads to an apparent anisotropy in the resistivity (measured parallel to and perpendicular to the plane of the film). Thus the magnitude of the apparent anisotropy (for nonoriented samples) offers a convenient means for quantifying the degree of dopant nonuniformity in trans-${(\mathrm{CH})}_{x}$. This technique is used to evaluate the uniformity achieved in ${[\mathrm{CH}{(\mathrm{As}{\mathrm{F}}_{5})}_{y}]}_{x}$ by conventional vapor-phase doping as compared with the slow-doping technique developed earlier for susceptibility studies. Using samples which have been demonstrated in this manner to be uniform, we reexamine the semiconductor-metal transition. From the transport data, we find that the better the uniformity in the distribution of dopant, the more abrupt is the transition at ${y}_{c}\ensuremath{\simeq}0.002$. A generalized soliton picture, involving delocalized carriers, appears to be implied by the combination of optical, magnetic, and transport data.