| 1. |
- Nilsson, P. O., et al.
(författare)
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Electronic structure of buried Si layers in GaAs(001) as studied by soft-x-ray emission
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52, s. R8643-
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Tidskriftsartikel (refereegranskat)abstract
- It is demonstrated that it is possible to investigate details of the electronic structure of an internal atomic monolayer using soft-x-ray-emission spectroscopy. The local and partial density of states of one monolayer and three monolayers of Si, embedded deep below a GaAs(001) surface, was extracted. Clear differences to the density of states for bulk Si were observed.
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| 2. |
- Varekamp, P R, et al.
(författare)
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Angle-resolved photoemission spectroscopy of the 1x1 ordered overlayers on iodine-saturated GaAs(001) and InAs(001)
- 1996
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 352, s. 387-390
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved valence band photoelectron spectra are collected from 1 X 1 ordered overlayers on I-2-saturated GaAs(001)-4 x 1, -c(2 X 8), and InAs(001)-c(8 x 2). A high-intensity dispersive surface state, located approximately 4.4 eV below the valence band maximum, is observed in each case. The state passes through an open lens in the projected bulk density of states and disperses symmetrically around the surface Brillouin zone edge. For all surfaces studied, the state is stronger when excited with the electric field polarized in the [110], as compared to the <(1)over bar 10>], azimuth. Since the state is independent of the termination of the initial surface, and since iodine bonds primarily to the outermost element, the state must result from delocalization of the electron states in the overlayer, and is not related to bonding with the substrate.
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| 3. |
- Varekamp, P R, et al.
(författare)
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Reaction of I-2 with the (001) surfaces of GaAs, InAs, and InSb .2. Ordering of the iodine overlayer
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:3, s. 2114-2120
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Tidskriftsartikel (refereegranskat)abstract
- The overlayer formed by the reaction of molecular iodine (I-2) with GaAs(001), InAs(001), and InSb(001) is investigated with synchrotron soft x-ray photoelectron spectroscopy (SXPS) and scanning tunneling microscopy (STM). Two components, separated by about 0.5 eV, are present in all of the I 4d SXPS spectra. At very low iodine coverages, the high binding energy (BE) component dominates. When the iodine coverage saturates, however, the two components have equal intensities. In contrast to GaAs and InAs, exposure of InSb(001)-c(8x2) to additional I-2 results in a further increase of the relative intensity of the low-BE component. STM images of I-2 covered InSb(001)-c(8x2) directly reveal the ordering in the overlayer. Islands are visible for submonolayer coverages, suggesting that adsorption occurs via a mobile precursor state. STM images feature occupies a 1x1 unit cell with the same spacing as bulk-terminated InSb(001). The other feature has a coverage of similar to 1/3 ML and is arranged in pairs oriented along the [110] azimuth.
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| 4. |
- Simpson, W C, et al.
(författare)
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Role of surface stoichiometry in the Cl-2/GaAs(001) reaction
- 1996
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Ingår i: Journal of Vacuum Science & Technology. A. Vacuum, Surfaces, and Films. - : American Vacuum Society. - 0734-2101 .- 1520-8559. ; 14:3, s. 1815-1821
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Tidskriftsartikel (refereegranskat)abstract
- The room-temperature reaction of Cl-2 with GaAs(001)-4x6, -c(2x8), and -c(4x4) surfaces is studied with synchrotron soft x-ray photoelectron spectroscopy. The chemical composition of the reacted surfaces is found to depend on the stoichiometry of the starting surface. In all cases, the reaction occurs stepwise, with Ga and As monochlorides formed prior to the dichlorides. The Ga-rich surface is initially more reactive than either of the As-rich surfaces and it forms more GaCl than the As-rich surfaces, which instead form more AsCl. The sticking coefficient for chlorine on GaAs(001) decays exponentially with coverage. A contribution from Cl atoms comprising the surface dichlorides is identified in the Cl 2p core-level spectra. (C) 1996 American Vacuum Society.
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| 5. |
- Varekamp, P R, et al.
(författare)
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Reaction of I-2 with the (001) surfaces of GaAs, InAs, and InSb .1. Chemical interaction with the substrate
- 1996
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 54:3, s. 2101-2113
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Tidskriftsartikel (refereegranskat)abstract
- InAs(001)-c(8x2), InSb(001)-c(8x2), and several reconstructions of GaAs(001) are exposed at room temperature to iodine molecules (I-2). Low-energy electron diffraction (LEED) and synchrotron soft x-ray photoelectron spectroscopy (SXPS) are employed to study the surfaces as a function of I-2 dose and sample anneal. In the exposure range studied, GaAs and InAs become saturated with I-2, resulting in removal of the clean surface reconstruction and the formation of a very strong 1x1 LEED pattern. Iodine bonds primarily to the dominant elemental species present on the clean surface, whether it is a group-III or -V element. The InSb(001)-c(8x2) reconstruction is also removed by I-2 adsorption, and a strong 1x1 LEED pattern is formed. SXPS data, in conjunction with scanning tunneling microscopy images, however, reveal that InSb(001)-c(8x2) does not saturate at room temperature, but is instead etched with a preferential loss of In. Heating the iodine-covered group-III-rich InAs(001)-c(8x2) and InSb(001)-c(8x2) surfaces causes removal of the iodine overlayer and transformation to a group-V-rich reconstruction. When the iodine-covered As-rich GaAs(001)-c(2x8) surface is heated to remove iodine, however, the c(2x8) reconstruction is simply regenerated.
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| 6. |
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| 7. |
- Andersson, C B M, et al.
(författare)
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Surface atomic structure of InAs((111)over-bar)2x2 and InSb((111)over-bar)2x2 studied by core level spectroscopy
- 1996
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 347:1-2, s. 199-206
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Tidskriftsartikel (refereegranskat)abstract
- Surface sensitive high resolution core level spectroscopy has been applied to the molecular beam epitaxy grown InAs((111) over bar)2 x 2 and InSb((111) over bar)2 x 2 surfaces. For both systems the In 4d core level consists of one dominating component while the Group V core levels are deconvoluted into four components. This analysis is consistent with a surface model where the topmost layer consists entirely of arsenic or antimony. In this model, Group V atoms form trimers bound to Group V atoms in the first double layer, leaving a single Group V rest atom per unit cell.
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| 8. |
- Hakansson, M C, et al.
(författare)
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The electronic structure of In- and As-terminated InAs(001) surfaces
- 1997
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Ingår i: Surface Science. - 0039-6028 .- 1879-2758. ; 374:1-3, s. 73-79
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Tidskriftsartikel (refereegranskat)abstract
- The InAs(001) 2 x 4 and 4 x 2 surfaces have been investigated by angle-resolved photoemission. The X(3) and X(5) points were found to be located 6.0 and 2.7 eV below the valence band maximum, respectively, and the dispersion of bulk bands along the Gamma-X direction in the bulk Brillouin zone were well described by a theoretical calculation. From angle-resolved valence band spectra measured along the high symmetry directions [110] and [1(1) over bar0$], three surface induced stares were identified on both the InAs(001)4 x 2 and the InAs(001)2 x 4 surface. (C) 1997 Elsevier Science B.V.
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| 9. |
- HAKANSSON, MC, et al.
(författare)
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PHOTOEMISSION-STUDY OF THE BAND-GAP ON CESIATED GE(111)1X1-AS
- 1995
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 52:16, s. 11646-11649
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Tidskriftsartikel (refereegranskat)abstract
- Deposition of small amounts of cesium on the As-terminated Ge(111) surface results in population of the lowest unoccupied surface state centered around the Gamma point in the surface Brillouin zone. By using angle-resolved photoemission we have directly determined the gap between this state and the lone-pair surface state to be 0.85 eV. This result provides support for recent quasiparticle band-structure calculations.
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| 10. |
- He, Z Q, et al.
(författare)
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As overlayer on GaAs(110) studied with photoemission
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:23, s. 16602-16607
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Tidskriftsartikel (refereegranskat)abstract
- As-terminated GaAs(110) surfaces were prepared on ex situ cleaved substrates by molecular-beam epitaxy. The surface stoichiometry was controlled by postgrowth As deposition. Photoemission from a surface covered with a monolayer As was investigated in detail using synchrotron radiation. Two different surface components were found in core-level spectra, which are interpreted as due to adatoms bonding to the surface anions and cations. In the valence-band spectra several surface states were identified, in analogy with previous reports on the isoelectronic Sb/GaAs(110) system. The polarization dependence is not the same, however, which leads us to the conclusion that the adlayer bonding mechanisms are different in the two cases.
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| 11. |
- He, Z Q, et al.
(författare)
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Band structure evolution in InAs overlayers on GaAs(110)
- 1996
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Ingår i: Applied Surface Science. - 0169-4332 .- 1873-5584. ; 104, s. 608-614
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Tidskriftsartikel (refereegranskat)abstract
- An angle-resolved photoemission study of MBE grown InAs/GaAs(110) hetero-structures was carried out to investigate the establishment of valence bands as a function of overlayer thickness. The valence band spectra were found to change gradually up to thicknesses well above 10 nm. The data are interpreted in terms of excitations within the overlayer from a combination of substrate and overlayer initial states, the former tailing into the overlayer.
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| 12. |
- Ilver, L, et al.
(författare)
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Quantum size effects in epitaxial ErAs on GaAs(001)
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 77:24, s. 4946-4949
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of very thin epitaxial ErAs layers on GaAs(100) is studied with angle resolved photoelectron spectroscopy. Clear evidence is found for confinement induced quantization of states around the Fermi level. From the dispersive properties of the quantum well states effective masses are obtained, representing electron motion parallel to the surface layers and orthogonal to the layers. We find, for the first time, that effective masses along equivalent bulk directions (XW) are significantly different in the thin layers. Furthermore, the bottom of the highest occupied band shifts towards the Fermi level when going from very thin to thick ErAs layers.
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| 13. |
- Mankefors, S., et al.
(författare)
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Ab initio calculations of soft-x-ray emission from Si(100) layers buried in GaAs
- 1998
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 58:16, s. 10551-10556
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of soft-x-ray emission spectra from Si(100) layers buried in GaAs are reported. The local densities of states for Si in As and Ga sites are found to be very different. By comparison with experimental data, this difference allows us to determine the relative amounts of Si in the two types of sites. In the case of a single Si layer we find that 63 (±5)% of the buried atoms are in Ga sites.
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| 14. |
- Mankefors, S., et al.
(författare)
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Theoretical investigation of soft x-ray emission from a Si(100) layer buried in GaAs
- 1998
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Ingår i: Vacuum. - : Elsevier. - 0042-207X .- 1879-2715. ; 49:3, s. 181-184
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of the soft x-ray emission spectrum have been carried out on a buried Si(100) layer in GaAs and compared with experimental data. We find that Si occupies Ga- as well as As-sites and that the local density of states is different for these two cases.
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| 15. |
- Mankefors, S., et al.
(författare)
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Theoretical investigations of As overlayers on InP(110) surfaces
- 1997
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Ingår i: Physical Review B Condensed Matter. - : American Physical Society. - 0163-1829 .- 1095-3795. ; 56:24, s. 15847-15852
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Tidskriftsartikel (refereegranskat)abstract
- As adsorption and interaction with InP(110) is investigated by means of total-energy minimization calculations. We find that the As-P exchanged configuration has higher energy than the As/InP(110) epitaxially continued layer structure (ECLS), for all types of As reservoirs considered. In the presence of an additional As layer in ECLS (i.e., 1.5 ML adsorbed As), however, the exchanged configuration is only slightly higher in energy than the nonexchanged one. We conclude that the As-P exchange process is energetically unfavorable, and should in any case not be complete at room temperature, as suggested in a recent report. Our conclusion is supported by results of a photoemission study, including As adsorption, desorption, and redeposition, according to which the process is nonreversible.
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| 16. |
- OLSSON, LO, et al.
(författare)
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ANOMALOUS QUENCHING OF PHOTOEMISSION FROM BULK STATES BY DEPOSITION OF CS ON INAS(100)
- 1995
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 52:3, s. 1470-1473
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Tidskriftsartikel (refereegranskat)abstract
- The effect of angle-resolved valence-hand photoelectron spectra from adsorption of small amounts of Cs on InAs(100)4 X 2 has been studied. It is shown that a bulk interband transition is totally quenched at a coverage of Cs that leaves the 4 X 2 reconstruction practically intact. The surface order was monitored by low-energy electron diffraction and photoemission from surface states. A shift of the surface Fermi level to well above the conduction-band minimum is also observed. It is proposed that the resulting development of a two-dimensional electron gas at the surface affects the bulk states probed in photoemission.
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| 17. |
- Olsson, L O, et al.
(författare)
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Charge accumulation at InAs surfaces
- 1996
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 76:19, s. 3626-3629
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Tidskriftsartikel (refereegranskat)abstract
- Angle-resolved photoelectron spectroscopy has been used to directly prove the existence of a charge accumulation layer at clean InAs surfaces. The formation of an accumulation layer is shown to be a common property of polar InAs surfaces, with the precise surface Fermi level position above the conduction band minimum determined by the surface geometry. The emission from states in the accumulation layer is studied with respect to its photon energy and angular dependence.
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| 18. |
- Olsson, L O, et al.
(författare)
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Core level and valence-band studies of the (111)2x2 surfaces of InSb and InAs
- 1996
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Ingår i: Physical Review B Condensed Matter. - 0163-1829 .- 1095-3795. ; 53:8, s. 4734-4740
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Tidskriftsartikel (refereegranskat)abstract
- The valence and core electronic surface states on the (111)2X2 surfaces of InSb and InAs have been studied by angle-resolved photoelectron spectroscopy. Similarities in data show that the vacancy-buckling model, which is known to describe the InSb(111)2x2 surface, also applies to InAs(111)2X2. Three surface valence bands are identified and their dispersions are mapped along symmetry directions in the surface Brillouin zone. The In 4d core levels show one surface shifted component while no surface shifted components of the Sb 4d or As 3d core levels could be resolved.
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| 19. |
- OLSSON, LO, et al.
(författare)
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SURFACE ELECTRONIC-STRUCTURE OF INSB(100)4X1 STUDIED BY ANGLE-RESOLVED PHOTOELECTRON-SPECTROSCOPY
- 1995
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Ingår i: Surface Science. - : Elsevier BV. - 0039-6028 .- 1879-2758. ; 331, s. 1176-1180
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Tidskriftsartikel (refereegranskat)abstract
- The surface electronic structure of the In-rich InSb(100)4 X 1 surface has been studied by angle-resolved photoelectron spectroscopy. To determine the origin of different contributions in spectra, direct bulk interband transitions were first identified using a semi-empirical band structure calculation and assuming direct transitions into free electron-like final bands. Three surface-induced features were identified and their dispersions have been mapped along symmetry directions of the surface Brillouin zone.
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| 20. |
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