Indium Overlayer Research Articles

Indium Growth on Reconstructed Si(111)√3 × √3 and 4 × 1 In Surfaces

The morphology and growth mechanism of nanostructured metals on semiconducting substrates determine crucially the electronic and physicochemical properties of these adsorption systems. In some cases, these properties are affected by modification of the interfacial geometry, induced by the metal adsorbate on the semiconducting substrate. Thus, in this work we investigate indium growth on the Si(111)√3 × √3 and Si(111)4 × 1 surfaces reconstructed by indium. The basic motivation of this study is to reveal how reconstruction of the silicon surface affects the growth mode and electronic properties of the indium overlayer. Therefore, the In/Si interface was mainly studied by Si 2p and In 4d photoemission spectra as well as by valence band measurements using synchrotron radiation. In addition, low-energy electron diffraction, Auger electron spectroscopy, thermal desorption spectroscopy, and electron energy loss spectroscopy were used to reveal the structure and adsorption states of the indium adsorbate on the re...

Surface electron accumulation in indium nitride layers grown by high pressure chemical vapor deposition

Surface termination and electronic properties of InN layers grown by high pressure chemical vapor deposition have been studied by high resolution electron energy loss spectroscopy (HREELS). HREEL spectra from InN after atomic hydrogen cleaning show N–H termination with no indium overlayer or droplets and indicate that the layer is N-polar. Broad conduction band plasmon excitations are observed centered at 3400 cm −1 in HREEL spectra with 7 eV incident electron energy which shift to 3100 cm −1 when the incident electron energies are 25 eV or greater. The shift of the plasmon excitations to lower energy when electrons with larger penetration depths are used is due to a higher charge density on the surface compared with the bulk, that is, a surface electron accumulation. These results indicate that surface electron accumulation on InN does not require excess indium or In–In bonds.

Carrier concentration and surface electron accumulation in indium nitride layers grown by high pressure chemical vapor deposition

Electronic and structural properties of InN layer grown by high pressure chemical vapor deposition have been studied by high-resolution electron energy loss spectroscopy (HREELS) and room temperature infrared reflection measurements. HREEL spectra after atomic hydrogen cleaning exhibit N–H bending and stretching vibrations with no indications of an indium overlayer or droplet formation. Broad conduction band plasmon excitations are observed centered at 3100–4200cm−1 at various locations across the surface in HREEL spectra acquired with 25eV incident electron energy. The plasmon excitations are shifted about 300cm−1 higher in spectra acquired using 7eV electrons due to higher plasma frequency and carrier concentration at the surface than in the bulk which indicates surface electron accumulation. Infrared reflectance data acquired at various spots across the surface showed a similar variation in bulk plasma frequency. A three phase thin film reflection model fitted to the infrared data yielded carrier concentrations from 8.2×1019to1.5×1020cm−3 and carrier mobilities from 105 to 210cm2∕Vs.

Investigation of In growth on W(1 1 0) by means of electron spectroscopies, low energy electron diffraction, thermodesorption and scanning tunneling microscopy

Investigations of indium growth on W(1 1 0) surface at submonolayer and monolayer coverages have been performed by means of photoelectron spectroscopy (XPS and UPS), low energy electron diffraction (LEED), thermodesorption spectroscopy (TDS) and scanning tunnelling microscopy (STM). Comparative electron spectroscopy, electron diffraction and STM studies indicated that at room temperature in the submonolayer range three indium-induced overlayer structures – (3 × 1), (1 × 4) and (1 × 5) have been formed. The (1 × 4) and (1 × 5) indium overlayers on W(1 1 0) observed close to completion of the first monolayer have been interpreted as slightly distorted In(1 1 1) monolayers in the Nishiyama–Wassermann orientation. It was found that the indium density in the (1 × 4) superstructure almost perfectly matches that of an In(1 1 1) monolayer, rendering this structure particularly stable. Further investigations performed by using imaging XPS studies and TDS method confirmed the results obtained by comparative electron spectroscopies and STM methods.

Electron energy loss spectroscopy, low energy electron diffraction, and auger electron spectroscopy study of Indium overlayers on Si(111) and Si(100) surfaces

In this paper, the behaviors of Indium overlayers on Si(111)7 × 7 and Si(100)2 × 1 surfaces have been investigated by low energy electron diffraction, electron energy loss spectroscopy, and auger electron spectroscopy. The behaviors of Indium overlayers on Si(111) and Si(100) surfaces are different. At room temperature, an intermixed interfacial phase was formed during Indium adsorption on Si(111) surface, but Indium was not intermixed with Si substrate on Si(100) surface. At the temperature of ∼550 °C and In coverage > 0.5 monolayer, the Si(100) surface could be completely faceted to {310} facets by Indium.

Influence of the structure of the electrodeposited antimony substrate on indium diffusion

Abstract The influence of the morphology and structure of antimony substrates on the diffusion and reaction process of an electrodeposited indium overlayer was investigated. The formation of the InSb intermetallic compound was studied by SEM-EDS and X-ray diffraction, at temperatures of 40, 70, 110 and 140°C. The antimony substrates, either crystalline or amorphous, were prepared by electrodeposition, the former being obtained in two different conditions, i.e. from a bath either not containing or containing the surface-active agent, Trylon B. The lowest indium diffusion coefficient was observed for the crystalline substrate prepared in the presence of the organic compound and the highest for the amorphous substrate, in spite of the higher surface roughness of the crystalline material. The values ranged from 0.35×10 −19 to 17.1×10 −19 m 2 s −1 , at 70°C. This behaviour was ascribed to the lower activation energy for In diffusion in the amorphous phase (53 instead of 65 kJ mol −1 ) which has a more open structure and lower density than the crystalline structure, due to the larger interatomic distances.

The structure of the indium-Si(111) ( [formula omitted]) monolayer surface

The structure of the ordered indium overlayer which forms at around one monolayer (ML) coverage at elevated temperature on Si(111)7 × 7 surfaces has been investigated by scanning tunneling microscopy (STM), scanning tunneling spectroscopy (STS) and low energy electron diffraction (LEED). The surface is characterised by a | 2 −1 1 2 | unit cell, designated in the following as ( 7 × 3 ), but two different local atomic configurations are observed to coexist at the same sample surface in atomically resolved STM images: a quasi-hexagonal arrangement with a local coverage of exactly 1 ML, and a quasi-rectangular arrangement with a local coverage of 1.2 ML. Both surface structures are metallic and reveal a very similar electronic structure in the STS spectra. The structures are discussed in terms of a close-packed In(001)-type overlayer and a straindashinduced distortion of a pseudomorphic overlayer.

In overlayers on Sb passivated GaAs

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.

Observation of indium on GaAs(110) surfaces by scanning tunneling microscopy

The surface structure of indium overlayers on cleaved p-type GaAs(110) is studied by scanning tunneling microscopy in ultrahigh vacuum. About 1 monolayer of indium was deposited on the surfaces at room temperature. We observed two types of indium adsorption. One is linear clusters along the [1 1 0] direction with corrugation amplitudes 1–2 Å above the GaAs surface. The other type, in which the second-layer indium atoms adsorb on the four-fold hollow site of the first-layer indium atoms, is also obtained near the linear islands. It is found that an In atom favors a Ga site rather than an As site for both types of adsorption.

Schottky barrier heights and interface chemistry in Ag, In, and Al overlayers on GaP(110)

We have carried out a study of the chemical reaction of silver, indium, and aluminium layers with cleaved GaP(110) surfaces using photoemission with synchrotron radiation. Core level photoelectron spectra show that silver and indium overlayers do not cause an interface reaction with GaP(110). The deposition of Al, on the other hand, leads to an extensive exchange reaction which also proceeds at low temperature, although influenced by changes in overlayer growth morphology. Surface band bending induced by the metallic overlayers was investigated as a function of deposition for n- and p-type material. In contrast to earlier findings, almost identical Schottky barrier heights for In and Ag deposition are obtained, despite the large difference in work function between these two metals. Results for Al also suggest that a small range of pinning positions is responsible for the Schottky barrier heights for junctions of these metals with GaP(110). We find that large peak shifts due to a surface photovoltage induced by the photoemission light source affect the determination of the Schottky barrier heights. This and other possible reasons for the discrepancy with earlier work are discussed.

Interfacial reactions between indium and anodic oxide of mercury cadmium telluride

The interfacial reaction between indium and anodic oxide of Hg0.8 Cd0.2 Te has been studied using x-ray photoelectron spectroscopy. It was found that the deposition of a thin layer (about 1 nm) of indium by either argon ion sputtering or by direct evaporation reduced some oxidized tellurium of the anodic oxide. The reduced tellurium was extracted to the indium overlayer and present as indium tellurides. However, the thin overlayer on the anodic oxide was found to be partially oxidized but not metallic.

Deposition of indium on Sb(111) single crystal: A low energy electron diffraction, Auger, and x-ray photoelectron spectroscopy interface investigation

Stepwise evaporations of indium have been done at room temperature on Sb(111) single crystals in order to study the interface and the InSb formation conditions. From the Auger measurements, we suggest a Stranski–Krastanov growth mode where the first monolayer seems to contain a significant amount of InSb. The InSb formation was further studied by Auger electron spectroscopy (AES) and x-ray photoelectron spectroscopy (XPS) by annealing a thick indium overlayer on Sb(111). Comparison is made to our measurements on an InSb single crystal and also to results from the literature. Low energy electron diffraction (LEED) shows the first monolayer to be disordered. However, the Sb single crystal covered with an indium overlayer restores a (2×2) or (1×1) LEED pattern after annealing, and InSb is formed in this case.

Reconstruction of aluminum and indium overlayers on Si(111): A systematic study with high-resolution electron energy loss spectroscopy and low-energy electron diffraction

We describe a detailed study of the different reconstructions obtained by depositing Al or In overlayers on Si(111)2×1 and Si(111)7×7 substrates, and of the reconstructions obtained by thermal annealing of these overlayers. We correlate the information obtained by low-energy electron diffraction (LEED) with high-resolution electron energy loss spectra (HREELS).

Indium overlayers on clean Si(100)2 x 1: Surface structure, nucleation, and growth

Indium overlayers on clean Si(100)2 x 1: Surface structure, nucleation, and growth

Structure changes in In/Au bilayers detected by electrical resistance measurements

The electrical resistance of In/Au bilayers was measured during deposition and heat treatment processes. The irreversible steps of increase in resistance which appear on the annealing curves are shown to be correlated with structure changes located at or near the InAu interface. The increase in electrical resistance which takes place during annealing depends on the indium overlayer thickness t 1 and the maximum annealing temperature of the bilayers. The first increase occurs for t 1 ⩾ 1.3 monolayers (1 monolayer  1.04 × 10 15 atoms cm −2) around a temperature T 1 which depends on the indium overlayer thickness. T 1 = 180 K for 1.3 monolayers ⩽ t 1 ⩽ 2 monolayers; this temperature decreases with increasing t 1 (2 monolayers ⩽ t 1 ⩽ 4 monolayers) and stays constant (160 K) for t 1 ⩾ 4 monolayers. The second increase occurs around 180 K and for t 1 ⩾ 3 monolayers. After these irreversible stages the amplitude of the quantum size effect oscillations observed during the growth of a second indium overlayer at 77 K is significantly reduced, as expected from an increase in the diffuse scattering of the conduction electrons at the AuIn interface.

Indium overlayers on clean Si(100)2×1: Surface structure, nucleation, and growth

The structure, nucleation, growth mechanisms, and morphology of In overlayers on clean Si(100)2×1 surfaces have been investigated as a function of In coverage θ and deposition temperature T s using reflection high-energy eletron (RHEED), low-energy electron diffraction (LEED), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM). The surface phase diagram for In on Si(100) was determined. Over the entire temperature range investigated, 30 to 600°C, In was found to interact with clean Si(100) surfaces through a Stranski-Krastanov mechanism in which the initially deposited In nucleated and grew two-dimensionally up to a coverage of between 2 and 3 monolayers (ML), depending upon T s, after which three-dimensional islands were formed. The structure of the two-dimensional layer, as well as the morphology of the islands, was dependent upon θ and T s. At deposition temperatures between 30 and 150°C, In formed a two-dimensional gas at coverages below 0.1 ML and an In(2×2) structure with chains of In dimers along 〈011〉 directions at coverages between ≈0.1 and 0.5 ML. Further increases in θ resulted in a transition to an In(2×1) structure while single-crystal elongated polyhedral-shaped islands exhibiting preferential growth along [011] and [01 1 ] directions were obtained at coverages above ≈ 3 ML. The introduction of even minute amounts of contaminants (≈ 0.01 ML) prevented the formation of the Si(100)2×2-In phase and resulted in the growth of epitaxial hemispherical fcc In islands on Si(100)2×1-In at θ ≳ 2 ML. For T s between 150 and 420°C, the initial In overlayer on clean Si(100) surfaces exhibited an In(3×4) structure and emispherical In islands were observed at coverages ≳ 2 ML. Above 420°C, a disordered In layer formed on top of the In(3×4) phase at θ≳0.5 ML while (310) Si facets were observed at θ > 0.5 ML and T s > 550°C. Indium deposition on Si(100)3×4-In surfaces (formed at T s > 150°C and then cooled to T s < 150°C before further deposition) resulted in the formation of hemispherical-shaped fcc In islands with a much higher number density than was observed for the elongated polyhedral-shaped In islands grown on Si(100)2×1-In surfaces under the same deposition conditions.

Surface and interface scattering of conduction electrons in Au/In double layers

The electrical resistance of metallic double layers of gold and indium was measured during the growth and heat treatment of an indium overlayer deposited onto a recrystallized gold film at 77 K. The initial increase in the electrical resistance observed during the condensation of the first (111) monolayers of indium onto the Au(111) crystal surface is partly ascribed to the scattering of the gold conduction electrons by the potential barrier localized at the AuIn interface. Analysis of the experimental results by means of a simplified model for the electrical conductance of double layers shows that some of the gold conduction electrons impinging on the interface are specularly reflected either without transmission through the interface or with transmission and specular reflection at the external free surface of the indium layer. Consequently, the electrical resistance of the double layer is sensitive to atomic scale variations in the roughness of the overlayer free surface as well as to the structural changes in the AuIn interface observed when the indium overlayer is heated for the first time above 120 K.