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ABSTRACT: The room temperature adsorption of molecular nitrogen on a InP(110) surface modified by a potassium overlayer is investigated by means of valence band and core level photoemission spectroscopy using synchrotron radiation. The results indicate no reaction between N2 and the clean InP(110), while the potassium-covered surface exhibits nitrogen uptake. Chemical shift at the P 2p core level suggests bonding with the anion and formation of InPNx nitride complex. In strong contrast with alkali-promoted silicon surfaces, reaction between potassium and the surface is found to be essential for the catalytic nitridation which is an indication of the role of defects. This study brings the first example of catalytic nitridation of a III-V semiconductor.
EPL (Europhysics Letters) 07/2007; 12(1):87. · 2.17 Impact Factor
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ABSTRACT: The electronic properties of Rb/Ge(111) and Na/Ge(111) interfaces are investigated by soft X-ray photoemission spectroscopy using synchrotron radiation. On both systems, alkali metal deposition results in the formation of a new well defined interface state below the Fermi level. This interface state is highly sensitive to oxygen exposure. For the Na/Ge(111) system, this interface state is found to resonate around a photon energy of 82eV. This resonance occurs within the adsorbate/substrate complex involving hybridization of their valence electrons. These results indicate that the nature of alkali metal-germanium bond should be understood in terms of covalent bonding, as observed for alkali metal-silicon surfaces. The existence of this interface resonant state brings the first example of an extra-atomic resonance involving both substrate and adsorbate electronic levels.
Physica Scripta 09/2006; 41(4):612. · 1.20 Impact Factor
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ABSTRACT: Semiconductor surface core level shifts are studied by use of selected overlayers. It is shown that certain nonreactive overlayers fully quench the surface core level shifts of the substrate without introducing additional interfacial components. The unique possibility of separately characterizing the bulk core level lineshape allows a precise determination of the surface core level shifts. This method is illustrated for the cleavage faces of Si and InP.
Physica Scripta 09/2006; 41(6):1034. · 1.20 Impact Factor
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ABSTRACT: GaAs band bending in the low adatom coverage regime (<1014 cm−2) has been investigated using photoelectron spectroscopy. Surface states originating from adatoms chemisorbed on the GaAs surface are responsible for this band bending, which can be described quantitatively by the depletion approximation. A relationship between the energy levels of surface donor states and the first ionization potential is established and is supported by recent theoretical calculations.
Physica Scripta 09/2006; 41(6):887. · 1.20 Impact Factor
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ABSTRACT: Interfaces between UHV-cleaved GaP (110) and overlayers of Sn, Sb, and Bi have been studied using soft X-ray photoemission spectroscopy. The substrate core level attentuation indicates that these three interfaces exhibit Stranski-Krastanov growth. The overlayer core level spectra (Sn 4d, Sb 4d, and Bi 5d) exhibit two components for coverages up to one monolayer, indicating that the adatoms form a zigzag chain overlayer as has been reported at the Sb/GaAs interface. The Ga 3d and P 2p surface components disappear as the first monolayer develops, and the remaining bulk components are used to determine various lineshape parameters of these core levels. The Schottky barrier formation at these interfaces has also been examined. The band bending at these interfaces occurs chiefly for coverages exceeding one monolayer, when islands are forming on the ordered layer. For all three of these interfaces the final surface Fermi level position is in the neighborhood of 1.0eV above the valence band maximum.
Physica Scripta 09/2006; 41(6):973. · 1.20 Impact Factor
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T Kendelewicz
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ABSTRACT: The room temperature reflectivity spectra of Cd1-xMnxTe mixed crystals for x up to 0.4 in the energy range from 1.5 to 14 eV have been investigated. A smearing out of the reflectivity maxima with growing x has been observed and attributed to manganese-induced chemical disorder. An additional structure at 4.6 eV interpreted as due to the transitions from the valence band to the Mn 3d6 states has been found. These results, together with previously published photoemission data, lead to the band picture of CdMnTe similar to the Adler-Feinleib type model proposed for transition metal chalcogenides with the correlation energy for d electrons of 9.6 eV.
Journal of Physics C Solid State Physics 11/2000; 14(13):L407.
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ABSTRACT: In an earlier letter [Appl. Phys. Lett. 68, 3090 (1996)] we reported results about heavily arsenic doped silicon crystals, where we unambiguously showed, based on x-ray standing wave spectroscopy (XSW) and other techniques, that electrically deactivated As remains essentially substitutional. In this article we present the analysis methodology that led us to said conclusion, and show how from further analysis it is possible to extract the compression or expansion of thin epitaxial layers. We report the evolution of the compression of highly As doped Si epitaxial layers as deactivation takes place. The XSW measurements required a very small thickness of the doped layer and a perfect registry between the substrate and the surface layer. We found larger values for compression than previously reported, which may be explained by the absence of structural defects on our samples that relax the interface stress. Our results show a saturation on the compression as the electron concentration increases. We also report an estimation of the small displacement from perfect substitutional positions suffered by deactivated As. © 1999 American Institute of Physics.
Journal of Applied Physics 01/1999; 85(3):1429-1437. · 2.17 Impact Factor
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ABSTRACT: Photoemission spectroscopy has been performed on Sb/GaAs. We have shown that Sb/nGaAs returns to near flatband (∼0.3 eV below the conduction‐band minimum) upon annealing. This is in contrast to previous results which demonstrated this behavior on p type (movement to ∼0.1 eV above the valence‐band maximum) but not on n‐type substrates [F. Schaffler, R. Ludeke, A. Taleb‐ibrahimi, G. Huges, and D. Rieger, J. Vac. Sci. Technol. B 5, 1048 (1987); R. Cao, K. Miyano, T. Kendelewicz, I. Lindau, and W. E. Spicer, Surf. Sci. 206, 413 (1988)] and in agreement with the results of Zahn et al. [T. Zahn, Technische Universitat Berlin (private communication)] showing analogous behavior in n‐type GaAs. Indium overlayers have been deposited on these surfaces and band bending, chemistry and overlayer morphology have been studied. Analysis of Ga (3d) and As (3d) spectra indicate that much stronger clustering is observed on p‐type than on n‐type substrates. Consistent with this assertion is that stronger chemistry is observed on n‐type substrates as is evident from the In (4d) and Sb (4d) spectra. The fact that the same clustering behavior is observed for In/GaAs for both n‐ and p‐type substrates suggests that the Sb interlayer is primarily responsible for the inequivalent clustering observed. Band bending results indicate that for Sb passivated substrates the Fermi‐level pins at 0.6 and 0.4 eV as opposed to 0.75 and 0.5 eV above the VBM for n and p‐type GaAs on the unpassivated surface.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1992; · 1.34 Impact Factor
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ABSTRACT: In a recent paper Hecht pointed out the influence of photovoltaic band flattening on photoemission measurements of Schottky barrier formation [M. H. Hecht, J. Vac. Sci. Technol. B 8, 1018 (1990)]. He further suggested that the low‐temperature (LT) overshoot observed on high‐doped p‐GaAs is due to photon‐induced charging of the GaAs surface. In this paper we evaluate this hypothesis based on a variety of LT band bending data. We conclude that the charging hypothesis fails to explain the following key aspects of the overshoot data. (1) The overshoot is dependent on the temperature of the interface formation and its influence on adatom clustering rather than the temperature at which the measurement is made. (2) The degree of overshoot has a simple dependence on the adatom ionization potential and electronegativity. (3) The overshoot is observed on very high doped substrates in which tunneling is anticipated to restore any nonequilibrium surface charge. A model involving adsorbate‐induced donor states at the overshoot level in the gap provides a more straightforward and complete explanation of these and other aspects of the overshoot data.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1991; · 1.34 Impact Factor
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ABSTRACT: Surface extended x‐ray adsorption fine structure (SEXAFS) has been used to investigate the structure of Sb on the Si(001) 2×1 surface. The coverage of Sb which remains after annealing thick layers at 375 °C, previously reported to be one monolayer (ML), is found in this work to form a disordered overlayer with three dimensional Sb clusters. This finding is concluded from the Sb L 3 absorption spectra which are similar for this coverage to that of bulk Sb. After a 550 °C anneal, Auger electron spectroscopy, and scanning tunneling microscopy (STM) show that about 1 ML of Sb remains. Phase and amplitude analysis of the Sb L 3 edge SEXAFS shows that the remaining Sb atoms occupy a modified bridge site with a Si–Sb bond length of 2.63±0.04 Å. The Sb atoms form dimers with a Sb–Sb bond length of 2.91±0.04 Å, which is almost identical to the bulk Sb–Sb bond length of 2.90 Å. The Sb atoms lie 1.74±0.06 Å above the Si(001) surface. STM confirms the dimer structure of the Sb overlayer.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1991; · 1.25 Impact Factor
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ABSTRACT: Chemical reactions on annealed Pd/GaAs(110) interfaces have been studied using soft x‐ray core level photoemission spectroscopy. Substantial surface segregation of As and formation of an As‐rich ternary phase close to the surface have been observed. Thicker Pd overlayers (22 and 52 Å) annealed to between 250 and 380 °C form reacted interfaces with chemically stable composition. As with the room temperature case, the reaction products due to annealing appear to be As rich close to the surface. Our results are compared with earlier transmission electron microscope studies and sources of some differences are discussed.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1991; · 1.25 Impact Factor
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ABSTRACT: The surface chemistry and band bending of the ammonium sulfide‐treated GaAs (100) surface has been studied using surface‐sensitive synchrotron radiation photoemission spectroscopy. We find that the treatment leaves the GaAs surface terminated with roughly a monolayer of sulfur bonded to both As and Ga atoms. An n‐type barrier height of 0.8 eV is measured. The thermal stability of the various chemical components is studied and various issues of the passivating mechanism are discussed.
Applied Physics Letters 09/1989; · 3.84 Impact Factor
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ABSTRACT: The formation of the Sb and Sn/InP(110) interfaces has been studied in situ by soft x‐ray core level photoemission spectroscopy. It is found that in both cases the growth of the first uniform monolayer is followed by the formation of large overlayer islands (Stranski–Krastanov mode). The dramatic sharpening of the substrate core levels at one monolayer of Sb indicates the formation of an ordered epitaxial overlayer. No such effect is seen for Sn for which the In 4d core level shows an indication of surface disruption. Despite the lack of order, this interface also remains mostly nonreactive. A straightforward analysis of the data for these particularly simple interfaces indicates nonequivalent shifts in the P 2p and In 4d core levels which are taken as a measure of the band bending. The origin of this discrepancy is shown to be related to an additional interface component in the In 4d core level data. The results of this study indicate that even for nonreactive InP interfaces one must take this into account in using core level photoemission data for quantitative band bending determination. Interestingly, both Sb and Sn, although nonreactive, appear to form Ohmic contacts to InP(110).
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1989; · 1.34 Impact Factor
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ABSTRACT: The interfaces of alkali metals (Cs and Rb) on GaAs and InP(110) surfaces prepared at 110 K low temperature have been studied using photoemission. At low temperature, multilayers of alkali metals with laminar growth can be obtained. The overlayer metallization is investigated by following the density of states near the Fermi cutoff, the free electron plasma loss, and the Fermi level movement at the semiconductor surfaces. Several criteria of metallicity are proposed. It is found that one monolayer of Cs or Rb is not metallic, and full metallicity is established at around two monolayers of coverage. The Fermi level movement relative to the semiconductor band edges as a function of alkali metal coverage has been closely followed. The semiconductor band bendings at low coverages are attributed to the surface‐donor states originating from alkali metal atom chemisorption. The Fermi level stabilization at these interfaces occurs when the overlayers become metallic. This pinning behavior is explained in terms of the metal‐induced gap states. The Fermi level pinning at the room temperature interfaces is also discussed and compared with the low‐temperature behavior.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1989; · 1.34 Impact Factor
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ABSTRACT: The band bending and the overlayer growth at the Sb/InP(110) interface has been studied with soft x‐ray photoemission spectroscopy. In agreement with previous works, our data indicate that 1 monolayer (ML) of Sb is growing in a laminar zig–zag fashion on the unrelaxed substrate. This is consistent with models previously applied to the Sb/GaAs interfaces. We, however, observe some puzzling behaviors unique to the Sb/InP(110) interface. First, we find that for this model system with simple morphology the core level shifts, routinely taken as a measure of the band bending, are different for In 4d and P 2p. This perhaps could indicate a presence of another component but also could indicate some problems in using photoemission in application to the quantitative band bending studies. Despite pronounced quantitative differences, we assumed that the core level movement is dominated by the band bending and find for both core levels a reversal of shift on n‐InP indicating reversal of the band bending from a maximum at ∼0.5 ML to a small value of 0.15±0.1 eV (0.1 or 0.2 eV depending on the core level monitored) for few monolayers of Sb. These data are consistent with previous results using Raman spectroscopy and electrical diode measurements which find Ohmic contacts for thick Sb overlayers on InP(110). Also consistent with these works, we find large band bending on p‐InP(110).
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1989; · 1.25 Impact Factor
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ABSTRACT: The resonant photoemission at the 3p photoabsorption threshold has been studied for room‐temperature grown and annealed Ni/GaAs interfaces and vacuum fractured NiAs crystals. For all samples studied strong resonance in the satellite line and an interference dip in the main photoemission line have been observed. Although, core level studies indicate complicated evolution of the interface with distinct new reaction phases, the line shape of resonances proves to be very insensitive to the details of reactivity.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1989; · 1.25 Impact Factor
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ABSTRACT: A photoemission spectroscopy study has been performed to investigate the 80 K low temperature (LT) to room temperature (RT) transition at the In/GaAs(110) interface. In/GaAs interfaces prepared at LT were slowly brought to RT while changes in overlayer morphology and band bending were observed via the Ga 3d and In 4d core level spectra. When several monolayers of In were deposited on LT p‐GaAs and this interface was subsequently warmed to RT, the band bending increased from the high‐coverage value of 0.5 eV to the 0.8 eV ‘‘overshoot’’ value that is seen at submonolayer coverages. From examination of the In 4d spectra, the In overlayer was found to cluster strongly upon warming, but In chemisorbed to the substrate remained between the clusters. The return of the overshoot that accompanies this In clustering may be explained by attributing the overshoot to states provided by the chemisorbed In. This reovershoot upon clustering further implies that the high‐coverage pinning of the In/LT p‐GaAs is due directly to the presence of the In overlayer rather than deposition‐induced defects in the GaAs.
Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 06/1989; · 1.25 Impact Factor
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ABSTRACT: Visible light from an argon ion laser (514.5 nm, 3 W/cm2) is seen to increase oxygen chemisorption on cleaved GaAs(110) surfaces up to a final coverage between one and two monolayers. Using photoemission spectroscopy to measure the oxygen coverage after simultaneous exposure of the surface to oxygen and light, we have determined that oxygen uptake for photoenhanced exposures is independent of sample temperature and doping type. In addition, significantly less enhancement is seen for weakly bound oxidizing molecules (N2O) relative to the effects with molecular oxygen. These results are explained by a photoenhancement mechanism in which energy is released in a surface recombination event, possibly in the form of nonthermal phonons, causing physisorbed gas molecules to dissociate and thereby overcoming a major rate limiting step of the reaction in the dark. This reaction mechanism is supported by calculations of the surface recombination rates and free carrier densities at the surface which show that only the recombination rate is correlated with enhanced oxygen uptake. Other mechanisms and experimental data are also discussed.
Applied Physics A 10/1988; 47(3):219-228. · 1.63 Impact Factor
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ABSTRACT: Schottky barrier formation at metal/n‐GaAs(110) interfaces has been studied with photoemission spectroscopy by varying the substrate doping from 4×10<sup>1</sup><sup>6</sup> to 5×10<sup>1</sup><sup>8</sup> cm<sup>-</sup><sup>3</sup>. The results challenge certain assumptions that have been made in past barrier formation models. For the clustered systems investigated—In, Ga, and Ag on n‐GaAs— the issue of lateral inhomogeneity of the interface state density is considered. Assuming that the interface states exist only beneath the clusters, lateral variation of the surface potential is expected. An increase of the substrate doping reduces the lateral depletion and should thereby affect this variation. However the core level line shapes exhibit no evidence of an inhomogeneous surface potential for any doping or coverage, even when the depletion length is in the neighborhood of the average cluster spacing. Consequently scenarios are considered in which pinning states are more uniformly distributed than the overlayer material itself. In modeling low‐coverage potential barrier formation, one might suppose that the net interface charge for a given low coverage is independent of the substrate doping. Under this assumption the total band bending for a given coverage is expected to be inversely proportional to the dopant concentration. For the systems examined in this study—In, Ga, Ag, Sn, and Sb on n‐GaAs—an inverse relationship between band bending and doping is observed, but the dependence is much weaker than a proportionality. In the context of a defect model of the interface charge states, this weakened dependence may be explained in terms of a defect state whose nature depends on the local Fermi level position, as has been suggested by Walukiewicz [J. Vac. Sci. Technol. B 5, 1062 (1986)]. The effect of metallic screening from the overlayer on the doping dependence of band bending is also consider-
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Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1988; · 1.34 Impact Factor
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ABSTRACT: The room temperature formation of the Cs/InP interface has been studied with soft x‐ray core level photoemission spectroscopy. The line shape analysis of the Cs 4d core level indicates that at submonolayer coverages Cs is bonded at both In and P sites. This is deduced from a large (1 to 0.55 eV) coverage‐dependent splitting of the Cs 4d into two doublets. The broadening at coverages close to a monolayer is consistent with the growth of an out registry overlayer as observed before for the Cs/GaAs interface. The energy shift of the substrate core level spectra indicates that the interface Fermi level stabilizes at about 0.8 eV above the valence band maximum which corresponds to relatively large (small) band bending for n‐type (p‐type) InP(110). This result is unexpected due to the small work function of Cs. The line shape and intensity analysis of the spectra indicates the formation of a laterally uniform overlayer and the lack of any noticeable chemical reaction.
Journal of vacuum science & technology. B, Microelectronics and nanometer structures: processing, measurement, and phenomena: an official journal of the American Vacuum Society 08/1988; · 1.34 Impact Factor
