Sb Segregation Research Articles

Surfactant-mediated epitaxy of relaxed low-doped Ge films on Si(001) with low defect densities

Fully relaxed, high-quality Ge layers were grown directly on Si(001) substrates by surfactant-mediated epitaxy at high temperature with large Sb flux. We attribute the low dislocation densities in our films to an abrupt strain relief via the formation of a regular array of 90° dislocations at the interface during the initial, microrough stage of growth. This mechanism of abrupt strain relaxation occurs exclusively under high Sb coverage at temperatures ∼700°C. The high growth temperature also enhances Sb segregation leading to a low background doping level of only (3–4×1016)cm−3. Thus, we regard surfactant-mediated epitaxy of relaxed Ge on Si(001) as a promising candidate for device application.

Segregation of Sn and Sb in a ternary Cu(1 0 0)SnSb alloy

Surface segregation studies of Sn and Sb in Cu(1 0 0)–0.14 at.% Sn–0.12 at.% Sb ternary alloy, have been done by making use of Auger Electron Spectroscopy. The method of Linear Temperature Ramp (LTR) was employed, whereby the sample was heated and cooled linearly at a constant rate. The positive heating rate showed both a kinetic segregation profile, as well as a narrow equilibrium segregation region, at higher temperatures. The equilibrium segregation profile was extended by cooling the sample. Sn was first to segregate to the surface due to its higher diffusion coefficient, mainly from a smaller activation energy E Sn. Sb, due to its higher segregation energy, eventually replaced Sn from the surface. The modified Darken model was used to simulate the profile yielding the following segregation parameters: D o(Sn) = 6.3 × 10 −6 m 2/s, D o(Sb) = 2.8 × 10 −5 m 2/s; E Sn = 175.4 kJ/mol, E Sb = 186.3 kJ/mol; Δ G Sn ° = 64.2 kJ / mol , Δ G Sb ° = 84.3 kJ / mol ; Ω Cu–Sn = 3.4 kJ/mol, Ω Cu–Sb = 15.9 kJ/mol and Ω Sn–Sb = −5.4 kJ/mol.

Sb Diffusion and Segregation in Amorphous Si Thin Films

Sb Diffusion and Segregation in Amorphous Si Thin Films

Growth of AlAsSb/InGaAs MBE-layers for all-optical switches

AlAsSb- and InGaAs(:Si)-layers have been grown by molecular beam epitaxy lattice matched to InP-substrates and characterized by X-ray diffraction, photoluminescence (PL) and capacitance–voltage profiling. Multi-quantum-well structures with 10 periods of 6 nm InGaAs-wells and 15 nm of AlAsSb-barriers were investigated in terms of interface abruptness and Si-doping. The PL full-width at half-maximum (PL-FWHM) at room temperature of undoped structures was reduced from 137 to 84 nm due to growth interruptions at interfaces under As-flow and with In and Sb segregation compensation. The Si doping by co-deposition of the InGaAs wells was compared to δ-doping centered to the wells. Uniformly doped InGaAs-wells with a Si concentration of 1×10 19 atoms/cm 3 showed an increased PL-FWHM of 178 nm due to degradation of interfaces. By δ-doping with 0.05 monolayers of Si in the middle of the wells the PL-FWHM could be reduced to 122 nm and the intensity of the signal could be increased compared to the uniformly doped quantum wells.

Preparation and Characterization of Antimony-Doped Tin Dioxide Electrodes. 3. XPS and SIMS Characterization

Several antimony- and antimony−platinum-doped tin dioxide electrodes supported on titanium have been characterized by X-ray photoelectron spectroscopy (XPS) for surface analysis and secondary-ion mass spectrometry (SIMS) for in-depth profile analysis. The surface analysis of the freshly prepared electrodes indicates that the Sb/Sn ratio in the electrode surface is similar to the nominal composition in the precursor solution, but the amount of Pt is higher than this nominal composition. The presence of platinum also produces the segregation of Sb near the electrode surface. The anodic polarization treatment of the electrode produces changes in its chemical state. The growth of a passivating hydroxide in the outer layer is the main cause of the deactivation of Ti/SnO2−Sb electrodes. The introduction of platinum in the layer prevents the hydroxide formation and modifies the deactivation mechanism of the electrode. The growth of an isolating TiO2 between the support and the active oxide produces the deactivat...

Reactivity and control of III–V surfaces for passivation and Schottky barrier formation

The N-for-As, P-for-As and Sb-for-As anion exchange reactions at GaAs surfaces, and the N-for-P anion exchange reaction at the GaP surface have been investigated with the aim at the formation of a thin high-gap surface layer for passivation of GaAs and GaP. Among the investigated anion exchange reactions, the P-for-As results in the formation of a ternary alloys GaP y As 1− y not effective for GaAs passivation. The Sb-for-As anion exchange does not occur and results in segregation of Sb at the GaAs surface. The Sb overlayer is effective in the chemical passivation of GaAs. The N-for-As anion exchange by a remote N 2–H 2 (a mixture of 97% N 2–3% H 2) radiofrequency plasma nitridation procedure forms a very thin (∼5 Å) GaN layer that is successful in the electronic and chemical passivation of GaAs(1 0 0) surfaces. The N 2–H 2 (a mixture of 97% N 2–3% H 2) nitridation has been found completely different from the pure N 2 nitridation which, in contrast, do not provide GaAs passivation, because the formation of Ga–N bonds accompanies with AsN and the segregation of elemental As at the GaN/GaAs interface. GaAs–GaN based Schottky structures have also been deposited and characterized by I– V measurements. A chemical and kinetic mechanism for the anion exchange reactions which takes into account also the competitive formation of PAs, AsN, and PN isoelectronic compounds is proposed.

Ultrathin type-II GaSb/GaAs quantum wells grown by OMVPE

Heterostructures containing monolayer (ML) and submonolayer GaSb insertions in GaAs were grown using organometallic vapour phase epitaxy. At the GaAs-on-GaSb interface, strong intermixing occurs due to the surface segregation of Sb. To form structures with relatively abrupt interfaces, a flashoff growth sequence, in which growth interruptions are employed to desorb Sb from the surface, was introduced. Reflectance-difference spectroscopy and high-resolution X-ray diffraction data demonstrate that interfacial grading is strongly reduced by this procedure. For layer structures grown with the flashoff sequence, a GaSb coverage up to 1 ML can be obtained in the two-dimensional (2D) growth mode. For uncapped GaSb layers, on the other hand, atomic force microscope images show that the 2D–3D growth mode transition occurs at a submonolayer coverage between 0.3 and 0.5 ML. Low-temperature photoluminescence spectra of multiple quantum well samples grown using the flashoff sequence show a strong quantum well-related peak which shifts to lower energies as the amount of Sb incorporated increases. The PL peak energies are consistent with a type-II band lineup at the GaAs/GaSb interface.

Misorientation dependence of intergranular embrittlement of Cu–2.0wt.% Sb bicrystals

Bicrystals of a Cu–2.0 wt.% Sb alloy with different [0 0 1] symmetric tilt boundaries were tensile tested at several temperatures from 77 to 743 K. The dependence of Sb segregation level at [0 0 1] tilt boundaries on the misorientation angle also was examined by energy-dispersive X-ray spectroscopy. The fracture behavior was sensitive to the misorientation angle and test temperature. Both the fracture behavior at 77 K and the Sb segregation level showed a good correlation with the grain-boundary energy of pure Cu. The higher the grain-boundary energy, the higher the Sb segregation level and the higher the degree of grain-boundary embrittlement .

Sb-Mediated Si heteroepitaxial growth on Ge(001)

Abstract Silicon heteroepitaxial growth on Ge(0 0 1) was studied with and without an Sb surfactant using scanning tunneling microscopy. Growth was studied at 570 K where Ge segregation was kinetically inhibited but Sb segregation was not. Without Sb, elongated rectangular 2D islands were initially observed. As the 2D islands grew they left behind long, straight trenches in the first layer that paralleled the island dimer rows. Second layer islands grew until they reached the trenches and formed double height steps. A barrier to descend the double height steps along with nucleation at domain boundaries in the second layer islands then caused 3D pyramids followed by more rounded 3D mounds to form. The 3D features caused the surface roughness to rapidly increase with Si coverage. In contrast, Si growth on Sb-terminated Ge(0 0 1) led to a high density of smaller, more isotropic islands. The growth was still not layer-by-layer, however, the surface roughness increased only very slowly with coverage. The smoother growth was attributed to the change in island shape. Because diffusion along dimer rows is much faster than across them, for the same island area, the downward flux is enhanced on square islands compared to islands elongated along their dimer row direction. In addition, the shape change prevents the long straight trenches from forming in the first layer that subsequently caused the 3D pyramids and mounds to form. The results for Si are compared with previous data for Ge homoepitaxy with and without Sb.

Sb surface segregation during epitaxial growth of SiGe heterostructures: The effects of Ge composition and biaxial stress

Antimony is the most widely used n-type dopant for Si molecular-beam epitaxy (MBE). However, because of surface segregation during growth, the control of doping profiles remains difficult. The case of ${\mathrm{S}\mathrm{i}/\mathrm{S}\mathrm{i}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ heterostructures is complicated by the existence of stresses, which may affect both the thermodynamics and kinetics of segregation. In this study, we analyze the segregation of Sb resulting from the MBE growth of ${\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}/\mathrm{Si}(100)$ heterostructures using secondary ion mass spectrometry as a function of (i) growth temperature $(200\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}l~T\ifmmode^\circ\else\textdegree\fi{}l~550\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}),$ (ii) germanium content $(0l~xl~0.2),$ and (iii) stresses (compressively strained and relaxed layers). We show that Sb segregation: (i) increases with temperature, (ii) increases with Ge content in biaxially compressed layers, (iii) decreases with Ge content in relaxed layers. The temperature variation indicates that Sb surface segregation during growth is kinetically controlled. The contrasting behaviors observed as a function of Ge content in stressed and relaxed layers can thus be explained by a decrease of the segregation enthalpy induced by Ge addition and an increase of near-surface diffusion in stressed layers.

Diffusion and segregation of shallow As and Sb junctions in silicon

The diffusion and segregation of Sb and As is investigated after low-energy implantation and annealing, both rapid thermal processing and furnace annealing. We demonstrate that the absence of transient enhanced diffusion effects for Sb facilitates the fabrication of significantly shallower junctions with less dopant segregation to the surface. It is shown that Sb implantation can be used to fabricate low-resistivity ultrashallow junctions suitable for source/drain extensions in n-type metal–oxide–semiconductor field effect transistors.

Quantitative measurement of the influence of growth interruptions on the Sb distribution of GaSb/GaAs quantum wells by transmission electron microscopy

We investigated the influence of growth interruptions on the morphology of molecular-beam epitaxy grown GaSb/GaAs multiquantum-well structures by transmission electron microscopy (TEM). Profiles of the chemical composition of the GaSb layers were deduced from high-resolution TEM images with the lattice fringe analysis method. We found clear indications of segregation of Sb in GaAs-on-GaSb for a sample grown with growth interruption before and after the growth of the quantum wells. Its efficiency R=0.78±0.03 was derived by fitting the measured composition profiles with the model of Muraki. Determination of the total amounts of deposited GaSb yields a higher amount of GaSb in a sample grown without interruption.

Antimony segregation in the oxidation of AlAsSb interlayers

The lateral wet oxidation of strained AlAsSb was studied. AlAs0.80Sb0.20 interlayers were grown on a GaAs substrate and capped with a lattice-matched In0.25Ga0.75As layer. The AlAsSb was oxidized between 350 and 450 °C. Oxidation temperatures >400 °C resulted in poor surface morphology and delamination. Oxidation of thicker AlAsSb interlayers (h≈2000 Å) resulted in metallic Sb layers forming between the AlOx and the semiconductor interfaces. The remaining Sb metal at the oxide–semiconductor interface was ∼15% oxidized. Lateral wet oxidation of thinner AlAsSb interlayers (h⩽500 Å) resulted in Sb inclusions at the oxide–semiconductor interface. The Sb inclusions were 1.5–2.0 μm in diameter and the inclusion thickness was approximately equal to the AlAsSb layer thickness. Methanol (CH3OH) was added to the water mixture with the intent to stabilize the otherwise unstable stibine (SbH3) such that Sb could be removed from the oxidizing structure. However, methanol addition resulted in a decreased oxidation rate and a change in the Sb precipitate morphology. The Sb inclusions observed in pure water oxidation changed to a Sb finger-like morphology with increasing methanol concentration. The Sb fingers were 1.0–2.0 μm wide and as long as the oxidation depth. Oxidation of AlAsSb interlayers h⩽200 Å were limited by the incorporation of Ga from the substrate and capping layer into the oxidation layer. Doping the oxidation AlAsSb interlayer 1×1018 cm−3 n type (Si or Te) did not result in any improvement in Sb segregation.

Spin polarization and magnetotransport of Mn–Sb alloys in magnetic tunnel junctions

The spin polarization of MnxSb1−x for x=0.35–0.45 has been explored via magnetic tunnel junctions using CoFe counterelectrodes and via superconducting tunneling spectroscopy using Al counterelectrodes. MnxSb1−x with x∼0.45 shows a tunneling spin polarization of ∼30% at 0.25 K, and a tunneling magnetoresistance of ∼18% at 10 K both of which are very similar to previously reported data on NiMnSb alloys. These results support the notion that surface segregation of Mn and Sb reduces the spin polarization of the purported half-metal NiMnSb.

Effect of Sb on coarsening of Fe particles in a Cu-Fe alloy

The influence of Sb on the coarsening behaviour of spherical α-Fe and γ-Fe particles in a Cu−Fe alloy has been investigated. The size of thparticles was determined by transmission electron microscopy and the Fe concentration in the Cu matrix by electric resistivity measurements. Adding Sb decreases the coarsening rate of the Fe particles, primarily via a reduction in the volume diffusivity of Fe in Cu. The pre-exponential factor and activation energy for volume diffusion are increased by the addition of Sb atoms in the matrix. The Sb addition changes the incoherent α-Fe−Cu interface energy by segregation of Sb at the incoherent interfaces but not the coherent γ-Fe−Cu interface energy.

Grain boundary segregation in Cu–Sb alloys

Equilibrium grain boundary (GB) segregation of Sb in Cu–Sb alloys was studied by the methods of Auger (AES) and X-ray photoelectron spectroscopy (XPS). On the basis of Langmuir–McLean isotherm, the atomic fraction of Sb ( X b 0) at the first layer was calculated provided that all available sites at the first layer were filled and equilibrium between the first layer and the volume was reached. The values of ( X b 0) do not exceed atomic concentration of Sb in the nearest chemical compound in equilibrium with solid solution according to the phase diagram. The segregation capacity of grain boundaries in Cu-based alloys averages between 0.38 and 0.65 of Sb monolayer. The enthalpy of Sb segregation is equal to −8.9 kJ mol −1.

Sequential segregation of Sn and Sb in a Cu(111) single crystal

AbstractThe sequential segregation of Sn and Sb to the surface of a Cu(111) single crystal was measured in the temperature range 400–1100 K by Auger electron spectroscopy. It was found that Sn with the higher diffusion coefficient first segregates to the surface and then is replaced by the slower‐segregating Sb. The results were fitted by a ternary segregation model yielding segregation energies (ΔGSn = 76.3 kJ mol−1, ΔGSb = 95.9 kJ mol−1), interaction parameters (ΩSnCu = 3.8 kJ mol−1, ΩSbCu = 16.2 kJ mol−1, ΩSnSb = −5.3 kJ mol−1) and diffusion coefficients (D0(Sn) = 1.8 × 10−5 m2 s−1, ESn = 173 kJ mol−1, D0(Sb) = 6.0 × 10−5 m2 s−1, ESb = 205 kJ mol−1) for both species. The validity of the interaction coefficients and segregation energies was verified using the Guttman equations for equilibrium segregation in ternary systems. Copyright © 2003 John Wiley & Sons, Ltd.

Antimony segregation in GaAs-based multiple quantum well structures

Sb segregation effects have been studied in structures grown by organometallic vapor phase epitaxy. The structures are formed by periodic exposure of the GaAs (0 0 1) surface to trimethylantimony (TMSb), followed by GaAs growth. Reflectance-difference spectra obtained during growth show a strong influence of Sb on the surface reconstruction, reducing the concentration of As dimers. Transmission electron microscope images and X-ray diffraction (XRD) measurements show that a periodic multiple quantum well (MQW) structure is formed by the TMSb/GaAs growth sequence. A fraction of the deposited Sb is incorporated as a one monolayer thick Sb-rich quantum well in each period. The incorporation of impurity Sb, as the GaAs layers are grown, results in the formation of a graded GaAs 1− x Sb x barrier layer above each QW layer. The impurity profile inferred from XRD measurements is in good agreement with a one-dimensional segregation model based on the partitioning of Sb between the growing barrier layer and a surface floating layer. The Sb floating layer is shown to desorb under exposure to tertiarybutylarsine.

Application of automated crystallography for transmission electron microscopy in the study of grain-boundary segregation

Analytical Electron Microscopy (AEM) has brought significant progress in the study of grain-boundary segregation. Using X-ray energy-dispersive spectrometry (XEDS) in the AEM, elemental segregation information can be related to the crystallographic character of the same boundary via conventional Transmission Electron Microscope (TEM) diffraction techniques. While significant efforts have been made to improve XEDS analysis of sub-nanometer segregation layers, the methods for crystallographic characterization of grain boundaries have remained the same for several decades and labor-intensive processes. Recently, a method termed Automated Crystallography for TEM (ACT) was developed, which automates crystallographic characterization of grains under TEM observation. In the present work, we combine ACT and X-ray mapping via EDS in AEM for the study of Sb grain-boundary segregation in a rapidly solidified Cu–0.08wt% Sb alloy. In contrast with previous reports, a large degree of anisotropy in Sb segregation level between different boundaries is found. ACT results suggest that one of the several grain boundaries observed with no detectable Sb segregation is very close to a Σ3 coincidence-site lattice structure. The reason for the observed anisotropy in the present alloy is discussed, based upon McLean's theory of segregation.

Antimony-induced embrittlement of [011] symmetric tilt boundaries in copper bicrystals

Copper bicrystals with different [011] symmetric tilt boundaries doped with Sb were tensile tested at several temperatures from 77 to 773 K. The fracture behavior was sensitive to the misorientation angle, Sb doping time, and test temperature. Grain boundaries were more embrittled with increasing the Sb doping time, though their tendency was also dependent on the misorientation angle. The degree of embrittlement of grain boundaries became lower as the test temperature increased to about 500 K, while it became higher again at higher temperatures. The segregation of Sb at [011] tilt boundaries also was systematically measured by energy-dispersive X-ray spectroscopy. A strong correlation was found among the fracture behavior at 77 and 773 K, grain-boundary segregation level of Sb, and grain-boundary energy before Sb doping: a higher-energy boundary has a higher level of Sb segregation and fractures more easily at a lower tensile stress.