N. G. Stoffel

Fermi-Level Pinning and Chemical-Structure of Inp-Metal Interfaces

We have used soft x‐ray photoemission spectroscopy (SXPS) to investigate the dependence of Fermi‐level pinning on chemical structure at InP–metal interfaces. SXPS core level spectra of Al, Ti, Ni, Au, Pd, Ag, and Cu on UHV‐cleaved InP(110) surfaces reveal evidence for semiconductor outdiffusion, metal indiffusion, metal‐anion bonding and metal‐cation alloying. Corresponding Fermi‐level movements indicate a range of pinning positions at significantly different energies within the n‐type InP band gap. These results demonstrate that the Schottky barrier heights depend sensitively on changes in interface chemical bonding and diffusion, which strongly affect the type of electrically active sites and interfacial layers formed.

Nature of the Band Discontinuities at Semiconductor Heterojunction Interfaces

Abstract A clear correlation was found between experimental heterojunction valence-band discontinuities locally measured by photoemission spectroscopy and the LCAO results of the Harrison model. In particular, we found that the theoretical discontinuities are accurate within 0.1–0.15 eV for lattice-matched interfaces. Empirical corrections for the bond-length difference in lattice-mismatched interfaces generally improve the agreement between theory and experiment.

Atomic and electronic structure of InP–metal interfaces: A prototypical III–V compound semiconductor

Soft x‐ray photoemission spectroscopy and electrical measurements of UHV‐cleaved InP–metal interfaces reveal that the interface abruptness on an atomic scale, the stoichiometry of semiconductor diffusion into the metal overlayer, and consequently the Schottky barrier height depend on the strength and nature of interface chemical bonding. For InP and other III–V compound semiconductors, these atomic and electronic features can be controlled extrinsically by reactive metal interlayers. Thus a chemical framework systematically accounts for the electrically‐active sites created during Schottky barrier formation at III–V compound semiconductor–metal interfaces.

Systematics of Chemical-Structure and Schottky Barriers at Compound Semiconductor Metal Interfaces

Note: Univ wisconsin,dept phys,madison,wi 53706. Brillson, lj, xerox corp,webster res ctr,800 phillips rd,webster,ny 14580.ISI Document Delivery No.: RP223 Reference LSE-ARTICLE-1983-001doi:10.1016/0039-6028(83)90539-3 Record created on 2006-10-03, modified on 2017-05-12

Electron and photon stimulated desorption of positive ions from alkali halide surfaces

Note: Univ wisconsin,dept phys,madison,wi 53706. Pian, tr, bell tel labs inc,murray hill,nj 07974.ISI Document Delivery No.: QV061 Reference LSE-ARTICLE-1983-013 Record created on 2006-10-03, modified on 2017-05-12

Microscopic Investigation of the Band Discontinuities at the Silicon-Germanium Heterojunction Interface

Abstract The formation of interface energy band discontinuities has been directly monitored on Ge-covered Si(111) surfaces with photoemission spectroscopy using synchrotron radiation. The final magnitude of the band discontinuities is not consistent with the linear combination of dipole-layers which leads to the “electron affinity rule”. Strong modifications of the local density of states occur during the formation of the heterojunction and the experiments indicate that the interface is abrupt on a microscopic scale.

Schottky-Barrier Modulation at Metal Contacts to Cds and Cdse

Soft x‐ray photoemission spectroscopy measurements have been used to study the pinning position of the surface Fermi level as well as the nature of the electrostatic band bending for single and interlayer metal contacts to ultrahigh‐vacuum‐cleaved CdSe and CdS (1010) surfaces. Single metal (Al,Au) contacts are found to exhibit a one‐to‐one correspondence between the pinning position and the effective Schottky barrier height as measured by in situ C–V and I‐V analyses. However, a fundamentally different mechanism of barrier modulation is indicated for interlayer contacts, i.e., contacts formed by interspersing an ultrathin reactive metal interlayer (Al) between the semiconductor and a noble metal contact (Au). Core level broadenings as a function of photon energy are interpreted in terms of sharp band bending at the surface, leading to the possibility of quantum mechanical tunneling through the barrier. This barrier narrowing effect is attributed to an indirect doping effect as a consequence of metal–semi...

Photoemission studies of heterojunction interface formation: Ge–GaAs(110) and Ge–Si(111)

A comparison between the formation mechanisms of Ge–GaAs(110) and Ge–Si(111) interfaces is presented. The localized valence band states and core‐level states were detected by photoemission spectroscopy with synchrotron radiation. Evidence was found that both kinds of interfaces are sharp and that Ge forms smooth overlayers at room temperature. The shifts in energy of the localized electronic states saturates at a much earlier stage of the interface formation for Ge–GaAs than for Ge–Si. The measured band discontinuities sharply disagree with the predictions of ’’linear’’ interface models. More sophisticated interface models give band discontinuities in excellent agreement with our experimental results for Ge–GaAs—while no satisfactory theoretical explanation is currently available for our Ge–Si results.

A solution of the core-exciton issue for silicon and germanium☆

Note: Univ wisconsin,ctr synchrotron radiat,stoughton,wi 53589. Margaritondo, g, univ wisconsin,dept phys,madison,wi 53706.ISI Document Delivery No.: KP659 Reference LSE-ARTICLE-1980-005 Record created on 2006-10-03, modified on 2017-05-12

Secondary illumination effects in the photoemission spectra of GaAs and CdS

Abstract The photoemission spectra of GaAs and CdS are dramatically affected by secondary illumination of the sample. Using synchrotron radiation and a computer lineshape analysis we demonstrate that valence band and core-level spectral features are all rigidly shiftedin energy by a few tenths of an electronvolt under secondary illumination. This provides conclusive evidence that photovoltaic band-bending changes are the only cause of these effects and rules out other possible mechanisms. It is therefore right to use these phenomena for quantitative studies of band bending effects and of ultralow densities of extrinsic or intrinsic surface states.