Sb Surface Research Articles

Sb surface segregation effect on the phase separation of MBE grown InAsSb

Mechanism of the phase separation observed in molecular beam epitaxial (MBE) grown InAsSb is investigated. We have reported that the alloys grown at or below ∼400°C show phase separation whereas the expected critical temperature ( T c) from the DLP model is 303°C. The phase-separated alloys consist of two alternating plates with different alloy compositions lying approximately parallel to the layer surface. The structural studies by transmission electron microscopy (TEM) showed that the alternating plates are ∼50 nm thick relatively uniform InAs-rich plates and ∼20 nm thick InSb-rich plates containing dense misfit dislocations. We believe that the spontaneous formation of such platelet structures at such temperatures is not associated with the spinodal decomposition but is induced by the Sb surface segregation. To confirm this model, InAsSb are grown below the critical temperatures with a periodic annealing during the growth to enhance desorption of the excess Sb accumulated on the growth surface due to the Sb surface segregation. With sufficient annealing time, no platelet structures are observed, i.e., homogeneous InAsSb form inside the empirical miscibility gaps.

Photoelectron diffraction study of the [formula omitted] surface-core-level-shift of the Si([formula omitted])(1×2)-Sb surface

Structural parameters of the Si(001)(1×2)-Sb surface were optimized by photoelectron diffraction (PED) of Sb4d peaks. The optimized parameters are 3.17±0.1 Å for Sb-dimer bond length and 1.78±0.1 Å for the layer spacing between Sb and the first layer Si. The main origin of a surface-core-level-shifted (SCLS) component in Si2p core-level spectra is identified by SCLS-PED to be the first layer Si atoms connected to Sb dimers. Another SCLS component reported previously was not observed, which indicates that this SCLS component is related to some defects on the (1×2)-Sb surface.

Scanning Tunneling Microscopy Study of the c(4×4) Structure Formation in the Sub-Monolayer Sb/Si(100) System

Upon Sb desorption from a Sb-saturated Si(100) surface, the c(4×4) structure formed at about 0.25 monolayer Sb coverage. The c(4×4) reconstruction has been found to develop best when the surface is slightly contaminated, plausibly, by carbon. The Si(100)-c(4×4)-Sb surface shows up in the high-resolution filled state scanning tunneling microscopy images as being very similar to that of the recently reported c(4×4)-Si reconstruction. Here the main features of the Si(100)-c(4×4)-Sb structure are identified and the possible atomic arrangement is discussed.

Time dependent surfactant effects on growth of GaInP heterostructures by organometallic vapor phase epitaxy

It has been shown that adding the surfactant Sb during growth eliminates ordering in GaInP by destroying the P dimers on the reconstructed surface. Consequently, the understanding of ordering can provide fundamental information about the surface during growth. This paper reports on the use of the surfactant Sb to modulate the order parameter of GaInP to produce disorder-on-order-on-disorder (D/O/D) heterostructures. It was found that heterostructures grown without interruptions have graded interfaces, but heterostructures grown with interruptions have abrupt interfaces. Secondary-ion mass spectroscopy (SIMS) measurements on the heterostructure grown without interruptions indirectly suggests that the Sb surface concentration changed significantly during growth as triethylantimony was added and removed from the system. Consequently, time dependent surface photoabsorption (SPA) measurements were made to determine the change in the P dimer concentration with the addition of triethylantimony. Comparison of the transient time constants with the Langmuir model suggests that relatively high concentrations of Sb accumulate on the surface during growth of the disordered layers. In addition, the results suggest that a critical concentration of Sb on the surface is necessary before the material disorders. Using the surfactant Sb with interruption results in a powerful tool for controlling the surface during growth. This technique was used to produce a GaInP D/O/D heterostructure with a very thin (67 Å) ordered layer, sharp interfaces and good photoluminescence. The ability of this tool to produce advanced quantum well devices appears feasible.

Sb-covered GaAs(1 1 1)B-(3×8) surface: a theoretical study

We have performed a detailed theoretical study of the atomic structure and electronic states on the GaAs(1 1 1)B–Sb(3×8) surface using ab initio pseudopotential calculations. Different plausible Sb-trimer configurations between Sb-chain pairs have been considered. The equilibrium configuration is in agreement with recent scanning tunnelling microscopy and X-ray photoemission studies. The orbital natures of the highest occupied and lowest unoccupied surface states have been examined.

TOF analysis of reflection of low-energy light ions from solid targets using coaxial impact collision ion scattering spectroscopy (CAICISS)

The energy spectra of He and D particles reflected from the Si(1 1 1)- 3 × 3 Sb surface at the angle of π in the sub-keV regime have been studied by means of a CAICISS system. The quantum efficiency of the microchannel plate for the particle detector in the CAICISS system has been determined as a function of the kinetic energy from the comparison of the experimental peak intensity from Sb atoms in the sub-monolayer regime with the theoretical one. The latter is calculated by use of the elastic scattering cross-section derived from the Thomas–Fermi model of the screened Coulomb potential. The energy spectra of He particles backscattered from the Si(1 1 1) substrate on incidence of 2 keV He + ions have been also obtained by use of the quantum efficiencies determined and compared with the theoretical ones calculated on the large angle single deflection model.

The Preparation and Characterization of Platinum Based PbSb Surface Alloy Electrode

The Preparation and Characterization of Platinum Based PbSb Surface Alloy Electrode

Sb segregation in Si and SiGe: effect on the growth of self-organised Ge dots

The segregation and incorporation coefficients of antimony (Sb) in Si 1− x Ge x buried doped layers were investigated simultaneously using specific temperature sequences. We first showed an exponential kinetic evolution of Sb surface segregation in Si. In contrast such an evolution could not be observed in Si 1− x Ge x because of the Sb thermal desorption, at growth temperatures of 550°C. We also showed an increased surface segregation increasing with the partial Ge concentration in Si 1− x Ge x alloys, which was explained by a decrease of the kinetic barrier for Sb atoms mobility. It was, therefore, possible to determine the growth conditions to obtain a Si 1− x Ge x doped layer with a controlled incorporation level and a negligible surface segregation obtained by the thermal desorption of the Sb surface coverage. Finally, using Sb surfactant mediated growth, we found Ge dots with lateral sizes reduced by a factor of 2.8 and density multiplied by a factor of four as compared to dots directly deposited on Si(001).

Effect of the co-deposition of Sb and Si on surface morphology

Scanning tunneling microscopy (STM) is used to observe changes in the surface morphology of a Si (100) surface during the co-deposition of Sb and Si at 500°C. The initial deposition of only 0.01 monolayers of Sb is shown to modify the Si growth mechanism. The roughness of the surface is found to increase during the deposition of Si under a constant Sb flux where the Sb surface coverage is also increasing due to surface segregation. By holding the Sb surface coverage constant and varying the Si deposition, we find that the presence of Sb on the surface inhibits Si attachment at step edges producing three-dimensional stacked island formations. We show that heating the sample for 60 s at 800°C to desorb the surface Sb can return a planar morphology to the Si surface.

Sb-mediated Ge growth on singular and vicinal Si(001) surfaces: A surface optical characterization study

In this work, we apply Raman spectroscopy (RS) and spectroscopic ellipsometry (SE) to surfactant mediated growth (SMG) of Ge on Si(001) surfaces. Under molecular-beam epitaxy conditions, a growth temperature of $400\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and in the absence of a predeposited surfactant (Sb) monolayer, we show that SE can be used to determine the Stranski-Krastanov critical thickness for island formation. In the presence of a predeposited Sb monolayer, SE predicts that layer-by-layer growth is possible up to a Ge coverage of 20 monolayers (MLs). However, no evidence of relaxation through dislocation formation, known to exist in this coverage regime, could be detected. With RS, we present one of the first studies of Sb mediated growth on a vicinal Si(001) substrate. Two Sb surface related phonon peaks are identified, one associated with Sb dimers bonded to the Si(001) substrate $(130.5 {\mathrm{cm}}^{\ensuremath{-}1}),$ the other with Sb dimers on the grown Ge epilayer $(141 {\mathrm{cm}}^{\ensuremath{-}1}).$ The former disappears and the latter appears gradually with increased Ge coverage up to 3.5 MLs. This indicates that surfactant exchange occurs differently on vicinal Si(001) than on singular Si(001), where exchange has been shown to be complete by deposition of between 0.5--1.0 monolayer (ML). To explain this difference, step bunching must occur during the initial stages of growth on vicinal Si (001), leading to areas of preferred growth on the surface. At a higher Ge coverage of 20 MLs, theoretical predictions of the Raman shift for a strained pseudomorphically grown Ge layer show good agreement with the Raman data presented. This demonstrates that even at 20 ML coverage, some areas of unrelaxed Ge must still exist, pointing to inhomogeneities within the Ge epilayer, as predicted by our model for SMG on a step bunched Si(001) substrate.

Sb-induced surface stacking faults at Ag(111) and Cu(111) surfaces: density-functional theory results

Using the CASTEP computer code we have conducted structuraloptimization calculation in the generalized-gradientapproximation for theAg(111)(√3×√3)R30°-Sb andCu(111)(√3×√3)R30°-Sb surface phases with a viewto exploring the findings of several recent experimental studieswhich indicate that the outermost surface alloy layer in thesesurfaces contains substrate and Sb atoms in the hcp hollow sites, leading to a stacking fault at the alloy-substrateinterface. The results confirm that these structures do havelower total energy than the unfaulted geometries. In Ag(111) thestacking fault energy for a clean surface layer is especiallylow, and becomes negative in the presence of the partial Sbsubstitution. The relative energies of alternative Sb surface structures on Ag(111) are consistent with those of previoustheoretical calculations, while the detailed geometry of the twooptimal structures agrees well with experimental results.

Studies on thermal property and atomic structure of the (Bi,Sb)/Si(111) surface

The changes of atomic structure and the coverage of binary metals (Bi,Sb) at the Si(111) surface induced by thermal annealing have been studied by means of low energy electron diffraction (LEED), Auger electron spectroscopy (AES), and Rutherford backscattering spectrometry (RBS) techniques. It is shown that Bi and Sb form surface alloy of √3×√3 structure. Moreover, coaxial impact-collision ion scattering spectroscopy (CAICISS) has been used to determine the atomic structures of the (Bi,Sb)/Si(111) surface. The structural model for the Si(111)√3×√3-(Bi,Sb) surface is proposed on the basis of the polar- and azimuth-angle's dependence of the Si, Bi, and Sb intensities.

Quantum Size Effects in Metallic Overlayer Epitaxy

Ab-initio total energy calculations have been performed to study the stability and electronic structure of epitaxial Sb and close-packed Ag films on GaAs(110) surfaces. These are model metal-semiconductor systems that have been studied extensively experimentally. The method used is density functional theory within the pseudopotential approximation. These calculations provide information on the relaxation and structure of the Sb and Ag surface layers and the stability of the metal films as a function of the number of metal layers.

Composition and morphology of SiGe alloys grown on Si(1 0 0) using an Sb surfactant

The effect of using a surfactant during SiGe alloy growth was investigated. Previous studies of surfactant-assisted growth have focused on the properties of pure Ge films grown on Si or on pure Si grown after Ge. Using X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM), we have studied the Ge compositional profile and morphology of SiGe alloys grown by molecular-beam epitaxy on Si (1 0 0) with an Sb surfactant. Using XPS, we have found that Ge segregation occurs at the start of alloy growth in the presence of up to 1 monolayer (ML) of Sb surface coverage but that the amount of Ge segregation is less than without Sb. We did find, however, that 0.75 ML of Sb after alloy growth can completely suppresses Ge segregation into a subsequent Si capping layer. Using XRD and TEM, we have found that SiGe films grown with 0.8 ML of Sb did not relax appreciably but did produce a non-planar surface morphology having an abrupt chemical interface between the alloy layer and the capping layer. We also found that the use of 0.8 ML of Sb resulted in compositional fluctuations within the alloy. We propose that the use of the Sb surfactant resulted in a separation of Si and Ge during the growth of the alloy layer producing the observed Ge segregation, surface morphology and compositional fluctuations.

Structure of III-Sb(001) growth surfaces: the role of heterodimers

We have determined the structure of AlSb and GaSb (001) surfaces prepared by molecular beam epitaxy under typical Sb-rich device growth conditions. Within the range of flux and temperature where the diffraction pattern is nominally (1x3), we find that there are actually three distinct, stable (4x3) surface reconstructions. The three structures differ from any previously proposed for these growth conditions, with two of the reconstructions incorporating mixed III-V dimers within the Sb surface layer. These heterodimers appear to play an important role in island nucleation and growth.

Formula omitted] a surface phase with a variable composition

Using scanning tunneling microscopy, the changes in the morphology and atomic structure of the Si(111)5 3 ×5 3 -Sb surface during Sb desorption have been studied. It has been found that the Si(111)5 3 ×5 3 -Sb surface phase does not have a definite composition. In attempting to explain the 5 3 ×5 3 long-range order stability in a wide Si and Sb coverage range it has been suggested that Sb atoms partially substitute for the boundary Si dimers in the basic 5×5 dimer–adatom–stacking-fault structure. A possible model of the Si(111)5 3 ×5 3 -Sb reconstruction satisfying this requirement has been proposed.

Effect of Sb pre-deposition on the compositional profiles in MOVPE-grown InAsSb/InAs(1 1 1) multi-quantum wells

This paper describes the effect of Sb pre-deposition on the composition modulation in InAsSb/InAs strained-layer multi-quantum wells. The multi-quantum-well structures, grown by metal–organic vapor-phase epitaxy (MOVPE) on InAs (1 1 1) substrates, had periods of ≈20 nm and nominal InAs 0.8Sb 0.2 layer thicknesses of ≈4.5 nm. Sb surface coverages from 0 to 1.4 monolayers (ML) were deposited on the InAs surfaces during growth interruptions prior to alloy layer growth. With no pre-deposition, kinematical simulations of measured θ–2 θ X-ray diffraction (XRD) patterns yielded best fits for exponential composition profiles as expected for Sb segregation. The 1/ e Sb segregation lengths were 1.2–1.6 nm. When ≈0.8 ML of Sb was pre-deposited, XRD simulations indicated sharper InAsSb-on-InAs interfaces. Sb coverages of ⩾1 ML broadened the XRD superlattice reflections, indicating that interface roughness increased.

Defects and energy barriers in the Si(100)–Sb and Si(100)–As surfaces: a theoretical study

When one monolayer of Sb or As is adsorbed on Si(100), the surface shows a (2×1) reconstruction formed by symmetric ad-metal dimers on an almost ideal Si surface. In spite of the similarities, some experimental differences have been reported. Scanning tunneling microscope images show that in the Si(100) (2×1)–Sb surface the long-range order is broken up by a high density of antiphase domain boundaries. Similar defects are rarely observed in Si(100) (2×1)–As. Using local density functional theory, we have studied the structural and electronic properties of the Si(100) (2×1)–Sb and Si(100) (2×1)–As surfaces with a defect: one dimer is shifted to the trench between two rows. We have found that energetics crucially determines the formation and stability of the defects. In the case of Sb, the total energy is ∼0.01 eV per dimer higher than the ideal (2×1) structure. For As, this value is ∼0.30 eV per dimer. This difference can be traced down to the atomic structure: the As–As dimer bond is weakened by the disorder, while the Sb–Sb bond is almost unaffected. We have also calculated the energy barriers between the ordered surface and the one with defects.

A medium energy ion scattering study of the structure of Sb overlayers on Cu(111)

Using 100 keV H + ions, medium energy ion scattering (MEIS) has been applied to a study of Sb overlayers on Cu(111). Upon deposition of 10 ML of Sb at room temperature, considerable intermixing of Sb and Cu occurs in thick (100 Å) overlayers, forming a partially ordered alloy phase, of composition Cu 3Sb. Heating to 200°C produces a second ordered alloy phase with reduced Sb content, whilst heating to 305°C diffuses excess Sb into the bulk and produces an ordered Cu(111) ( 3 × 3 ) R30°Sb surface phase with 0.33 ML Sb. Comparison of blocking curves obtained from this phase with the results of simulations for a range of model structures leads to the conclusion that the Sb atoms substitute outermost layer Cu atoms, but this surface alloy layer is laterally displaced so that all constituent atoms occupy hcp hollow sites relative to the underlying Cu(111) substrate. In this stacking faulted surface layer, the layer spacings of the Sb and Cu atoms relative to the outermost underlying Cu surface layer have been determined to be 2.52±0.13 Å and 2.05±0.09 Å respectively. Some aspects of the methodology for the application of MEIS to surface structure determination and structural parameter precision estimation are addressed.

Ge concentration dependence of Sb surface segregation during SiGe MBE

Surface segregation of antimony atoms during Si 1− x Ge x molecular beam epitaxy (MBE) was studied by using the delta-doping technique. The segregation of Sb increases with increasing growth temperature and increasing Ge concentration of Si 1− x Ge x . This result is well explained by a two-state model in which the energy barrier to Sb surface segregation decreases with increasing Ge concentration of Si 1− x Ge x .