Photoemission study of alkali/GaAs(110) interfaces

Prietsch, M.; Domke, M.; Laubschat, C.; Mandel, T.; Xue, C.; Kaindl, G.

doi:10.1007/bf01307236

Cited by 117 publications

(34 citation statements)

References 31 publications

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“…1b) and the O 1s peak (not shown). Adsorption of the electropositive species like AM's on semiconductor surfaces induces downward bending of the substrate's band [20][21][22], whereas the electronegative species such as oxygen and halogen lead to upward band bending [22][23][24]. Therefore, Na-induced downward bending of the ZnO band is an indication that the Na adatoms are positively charged on the surface in the initial stages of adsorption.…”

Section: A Na Adsorption Processmentioning

confidence: 99%

Alkali-Metals on ZnO(10-10) Studied by Low-Energy Electron Diffraction and Photoelectron Spectroscopy

Ozawa

Satō

Oba

et al. 2005

e-J. Surf. Sci. Nanotechnol.

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The geometric and electronic properties of alkali metals (Na and Cs) on ZnO(1010) are investigated by means of photoelectron spectroscopy and low energy electron diffraction (LEED). Growth of the Na overlayer on ZnO(1010) at room temperature is characterized by layer-by-layer growth or monolayer growth followed by three-dimensional cluster growth. The Na adatoms in the first layer are in a cationic state, and the metallic phase is formed on top of the first cationic layer. Although Na deposition at room temperature does not yield any long-range ordered superstructure, annealing the Na-covered surface results in a (1×3) LEED pattern, and we propose the formation of the Na atomic chains along the Zn-O dimer rows. For the Cs adsorption system, the disordered overlayer by ionized Cs adatoms is also formed throughout the submonolayer coverage region. Unlike the Na adsorption system, heat treatment of the Cs-covered surface does not yield any ordered structure until all Cs adatoms desorb from the surface.

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Section: A Na Adsorption Processmentioning

confidence: 99%

Alkali-Metals on ZnO(10-10) Studied by Low-Energy Electron Diffraction and Photoelectron Spectroscopy

Ozawa

Satō

Oba

et al. 2005

e-J. Surf. Sci. Nanotechnol.

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“…Core-level PES experiments also attributed the strong band bending at the low coverage range to the donorlike empty state above the conduction band edge. [24][25][26] Assuming that the GaAs substrate feels one positive charge per adsorbed K dimer, a simple 1D electrostatic calculation shows that the area density of the K dimers ͑͒, which is required to bend the band by eV s , can be calculated as = ͑2⑀N A ͉V s ͉ / e͒ 1/2 , where ⑀ is the dielectric constant of GaAs, V s is the surface potential with respect to the bulk, N A is the concentration of the acceptor, and e is the elementary electric charge. The calculated area density of the K dimers for a 1.2 eV band bending is 1.2ϫ 10 13 cm −2 .…”

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confidence: 97%

“…23 In fact, the core-level PES measurement showed that the strong band bending ͑ϳ1 eV͒ occurred on the p-type GaAs͑110͒ surface at the beginning of the K adsorption process. 24 The observed slight difference could arise from the additional tip-induced band bending in the STM configuration. For the downward band bending, positive charges should exist at the surface.…”

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confidence: 97%

Structural and electronic properties of theK∕GaAs(110)surface

Ishida

Sueoka

2008

Phys. Rev. B

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Scanning tunneling microscopy and scanning tunneling spectroscopy were used to clarify the correlation between the geometric structure and the electronic properties of the K / GaAs͑110͒ surface. The K asymmetric chains induce a surface state localized in the vicinity of the Ga atoms, which indicates the bonding between the K atoms and Ga atoms. The observed energy position of the surface state suggested that the surface potential was changed by the K adsorption. The obtained results are compared with theoretical work in order to explain the electronic properties.Alkali metals adsorbed on III-V͑110͒ surfaces have been studied for decades due to the interest in the mechanisms of the Schottky barrier formation and the Fermi level pinning at metal-semiconductor interfaces. 1 These systems are thought to be the ideal playground for the investigation of metalsemiconductor interfaces due to the following reasons. ͑i͒ From a theoretical point of view, these systems provide a simplified model because only one valence electron at the outermost shell should be considered. ͑ii͒ Since the relaxation of the topmost atoms induces the movement of the surface states of the III-V͑110͒ surfaces out of the fundamental band gap, the metal induced states within the band gap can be easily investigated. However, alkali metals adsorbed on III-V͑110͒ surfaces exhibit complicated adsorption structures depending on their coverage. 2-8 As a consequence, it is difficult to investigate the correlation between the geometric structures and the electronic properties by using surface averaging techniques, such as photoemission spectroscopy ͑PES͒ and low energy electron diffraction. In PES experiments, the adsorption structure has to be indirectly deduced by, for example, monitoring the work function change. 9,10 On the other hand, scanning tunneling microscopy ͑STM͒ and scanning tunneling spectroscopy ͑STS͒ make it possible to correlate directly the structural and electronic properties. 11,13 However, most STM studies on these surfaces so far have focused on the geometric structures of the adsorbed alkali atoms. 2,5,7 Though a few papers have reported such STS data, only the width of the band gap obtained from the I-V curves was discussed to confirm whether the surface is semiconducting or not. 3,12 The lack of STS data may be attributed to the instability of the alkali atoms under a positive bias condition, 14,15 which makes the apex of the STM tip unstable.Controversial issues include the adsorption structures of the alkali atoms as well as certain electronic properties, such as the insulating behavior of the alkali adlayer and the charge transfer from the alkali atoms to the substrate atoms. 1 Some reports have explained the insulating behavior in terms of the Mott-Hubbard mechanism by assuming a single adsorption site for the alkali atoms. 16,17 On the other hand, Calzolari et al. proposed an alternative explanation for the insulating behavior by assuming the existence of two inequivalent adsorption sites as follows. 18 In their proposed struc...

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“…1/09/09 2 Adsorption of alkali metals on semiconductor surfaces has been investigated in most detail for silicon 1,2 and for the (110) cleavage face of GaAs, [3][4][5] for which the nature of chemical bonding, the amount of charge transfer, and the origin of the surface dipole have been essentially clarified. On the other hand, despite of technological applications, the fundamental aspects of adsorption on GaAs(001), including the difference in the adsorption mechanisms at the empty gallium-related and at the occupied arsenic-related dangling bonds is still far from being known.…”

mentioning

confidence: 99%

“…The situation becomes opposite for Θ Cs >0.3 ML, at which transfer occurs to As but no longer to Ga. Charge transfer to As atoms leads to surface disordering and destabilization and induces surface conversion from As-rich to Ga-rich (4x2)-GaAs(001) surface after annealing at a reduced temperature of 450°C.1/09/09 2 Adsorption of alkali metals on semiconductor surfaces has been investigated in most detail for silicon 1,2 and for the (110) cleavage face of GaAs, [3][4][5] for which the nature of chemical bonding, the amount of charge transfer, and the origin of the surface dipole have been essentially clarified. On the other hand, despite of technological applications, the fundamental aspects of adsorption on GaAs(001), including the difference in the adsorption mechanisms at the empty gallium-related and at the occupied arsenic-related dangling bonds is still far from being known.…”

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confidence: 99%

Cs-induced charge transfer on(2×4)-GaAs(001) studied by photoemission

et al. 2010

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Cesium adsorption on (2×4)-GaAs(001) was studied by photoemission and low -energy electron diffraction. The different Cs-induced changes of As 3d and Ga 3d core level spectra show that charge transfer is almost complete for Ga surface sites, but is negligible to surface As at a coverage Θ Cs < 0.3 ML. The situation becomes opposite for Θ Cs >0.3 ML, at which transfer occurs to As but no longer to Ga. Charge transfer to As atoms leads to surface disordering and destabilization and induces surface conversion from As-rich to Ga-rich (4x2)-GaAs(001) surface after annealing at a reduced temperature of 450°C.1/09/09 2 Adsorption of alkali metals on semiconductor surfaces has been investigated in most detail for silicon 1,2 and for the (110) cleavage face of GaAs, [3][4][5] for which the nature of chemical bonding, the amount of charge transfer, and the origin of the surface dipole have been essentially clarified. On the other hand, despite of technological applications, the fundamental aspects of adsorption on GaAs(001), including the difference in the adsorption mechanisms at the empty gallium-related and at the occupied arsenic-related dangling bonds is still far from being known. For the (2×4) As-rich surface, the early stages of Cs adsorption, characterized using both X-ray diffraction and theoretical calculations, 6 give rise to adsorption near both As dimers and Ga dangling bonds with a significant charge transfer only in the latter case.Here, we report investigation of the microscopic nature of the bonding between Cs and (2x4)-GaAs(001) using photoemission spectroscopy. The investigations were performed at the SU3 beamline of the SuperAco storage ring (Orsay, France), in a UHV chamber with a base pressure in the 10 -11 mbar range. The photoemission spectra were obtained using a hemispherical electron analyzer, at an overall energy resolution of the order of 0.15 eV at photon energy of 100 eV. Clean reconstructed surfaces of epitaxial p-GaAs(001) were obtained by using a treatment by HCl in isopropyl alcohol under dry nitrogen atmosphere, followed by introduction into ultra-high vacuum (UHV) and annealing to 450°C. 7 Low energy electron diffraction (LEED) investigations and measurements of the work function changes were performed in an independent setup by a retarding field method using a LEED gun. 8Several successive exposures to cesium (20, 30, and 50 minutes) were performed at RT using thoroughly outgassed dispensers in a vacuum not exceeding 10 -10 mbar. Using a previousAuger investigation, 9 we estimate that a deposition time of 50 minutes corresponds to a cesium coverage Θ Cs of about 50% of the saturation concentration, the latter concentration being taken as one monolayer (ML). The Cs 4d core level spectra (CLs), not shown here, are .50-1.55 were used. 11 For As 3d at Θ Cs <0.3ML , we have used two surface components.There is first a contribution S 1 , shifted by 0.62 eV to the higher BE side. This contribution is known to be caused by excess arsenic under the form of As dimers which are bonded t...

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Photoemission study of alkali/GaAs(110) interfaces

Cited by 117 publications

References 31 publications

Alkali-Metals on ZnO(10-10) Studied by Low-Energy Electron Diffraction and Photoelectron Spectroscopy

Alkali-Metals on ZnO(10-10) Studied by Low-Energy Electron Diffraction and Photoelectron Spectroscopy

Structural and electronic properties of theK∕GaAs(110)surface

Cs-induced charge transfer on(2×4)-GaAs(001) studied by photoemission

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