Photonic page buffer based on GaAs multiple-quantum-well modulators bonded directly over active silicon complementary-metal-oxide-semiconductor (CMOS) circuits: errata

Owing to printing errors, [Appl. Opt. 35, 2439 (1996)] several figures were illegible. The figures are reprinted and briefly reviewed.     

Strain accommodation in Ga-assisted GaAs nanowires grown on silicon (111)

We study the mechanism of lattice parameter accommodation and the structure of GaAs nanowires (NWs) grown on Si(111) substrates using the Ga-assisted growth mode in molecular beam epitaxy. These nanowires grow preferentially in the zincblende structure, but contain inclusions of wurtzite at the base. By means of grazing incidence x-ray diffraction and high-resolution transmission electron microscopy of the NW-substrate interface, we show that the lattice mismatch between the NW and the substrate is released immediately after the beginning of NW growth through the inclusion of misfit dislocations, and no pseudomorphic growth is obtained for NW diameters down to 10 nm. NWs with a diameter above 100 nm exhibit a rough interface towards the substrate, preventing complete plastic relaxation. Consequently, these NWs exhibit a residual compressive strain at their bottom. In contrast, NWs with a diameter of 50 nm and below are completely relaxed because the interface is smooth.     

Fabrication of vertical ZnO nanowires on silicon (100) with epitaxial ZnO buffer layer

Vertical ZnO nanowires were successfully grown on epitaxial ZnO (002) buffer layer/Si (100) substrate. The nanowire growth process was controlled by surface morphology and orientation of the epitaxial ZnO buffer layer, which was deposited by radio-frequency (rf) sputtering. The copper catalyzed the vapor-liquid-solid growth of ZnO nanowires with diameter of approximately 30 nm and length of approximately 5.0 microm. The perfect wurtzite epitaxial structure (HCP structure) of the ZnO (0002) nanowires synthesized on ZnO (002) buffer layer/Si (100) substrate results in excellent optical characteristics such as strong UV emission at 380 nm with potential use in nano-optical and nano-electronic devices.     

Structural phase control in self-catalyzed growth of GaAs nanowires on silicon (111)

Au free GaAs nanowires with zinc blende structure, free of twin planes and with remarkable aspect ratios, have been grown on (111) Si substrates by molecular beam epitaxy. Nanowires with diameters down to 20 nm are obtained using a thin native oxide layer on the Si substrates. We discuss how the structural phase distribution along the wire length is controlled by the effective V/III ratio and temperature at the growth interface and explain how to obtain a pure twin plane free zinc blende structure.     

Effect of graded buffer design on the defect structure in InGaAs/GaAs (111)B heterostructures

In this work, the defective structure of InGaAs/GaAs (111)B has been studied, using different types of substrate misorientation and incorporating different types of graded buffer layers. The formation of deformation twins has been observed to be independent of misorientation direction, but with a distribution dependent on the substrate misorientation angle. Samples grown on 2° misoriented substrates showed long twins with the majority of them formed with only one {111} variant. The use of a step-graded structure achieved a threading dislocation (TD) density improvement, although it was not able to alter the density of plastic relaxation occurring through twins. Twin nucleation occurred at the surface, being controlled by the superficial step density and not by the relaxation sequence of the structure. In the perpendicular direction to the off-cut, the linearly graded layer structures showed a higher twin density and no misfit dislocations (MD) were observed. A diffraction pattern study indicated an epilayer tilt in the off-cut direction with respect to the substrate. This additional tilt, probably due to the introduction of dislocations with a preferential Burgers vector, produced a superficial step density increase and, therefore, strain relief occurred by twins in preference to MDs.     

Synthesis, morphology and compositional evolution of silicon nanowires directly grown on SnO(2) substrates

We here propose an all-in situ method for growing vapor-liquid-solid (VLS) silicon nanowires (SiNWs) directly on SnO(2) substrates in a plasma-enhanced chemical vapor deposition system. The tin catalysts are formed by a well-controlled H(2) plasma treatment of the SnO(2) layer. The lowest temperature for the tin-catalyzed VLS SiNWs growth in a silane plasma is ～250?°C. The effects of substrate temperature and H(2) dilution of silane on the morphology and compositional evolution of the SiNWs were systematically investigated. The catalyst content in the SiNWs can be effectively controlled by the deposition temperature. Moreover, enhanced absorption (down to ～1.1?eV) is achieved due to the strong light trapping and anti-reflection effects in the straight and long tapered SiNWs.     

Growth of InN layers on Si (111) using ultra thin silicon nitride buffer layer by NPA-MBE

Indium nitride (InN) epilayers have been successfully grown by nitrogen-plasma-assisted molecular beam epitaxy (NPA-MBE) on Si (111) substrates using different buffer layers. Growth of a (0001)-oriented single crystalline wurtzite-InN layer was confirmed by high resolution X-ray diffraction (HRXRD). The Raman studies show the high crystalline quality and the wurtzite lattice structure of InN films on the Si substrate using different buffer layers and the InN/β-Si₃N₄ double buffer layer achieves minimum FWHM of E₂ (high) mode. The energy gap of InN films was determined by optical absorption measurement and found to be in the range of ~ 0.73-0.78 eV with a direct band nature. It is found that a double-buffer technique (InN/β-Si₃N₄) insures improved crystallinity, smooth surface and good optical properties.     

Area selective epitaxy of indium phosphide on silicon (100) substrates without buffer layers by liquid phase epitaxy

Area selective epitaxy (ASE) of InP was performed by liquid phase epitaxy on Si (100) substrates without the use of buffer layers. At the start of epitaxy, the growth temperature was rapidly lowered to obtain high supersaturation. Epitaxial growth was then carried out at constant temperature. While small InP nuclei were observed in the broader open areas, ASE layers and layers showing slight epitaxial lateral overgrowth were formed in the narrow openings. Etch pit density of the InP ASE layers on Si is dependent on the length of open seed region and X-ray diffraction results indicate that the lattice strain in the InP nuclei on the Si substrate was fully relaxed.     

The effect of an SiO(2) buffer layer on the SAW properties of ZnO/SiO(2)/GaAs structure

The effect of an SiO(2) buffer layer on the surface acoustic wave (SAW) properties of ZnO/SiO(2)/GaAs structure is examined. Both theoretical and experimental results show that the coupling coefficient is increased appreciably by providing an SiO(2 ) film between the ZnO film and the GaAs substrate. Adding an SiO (2) film is also beneficial to the promotion of quality of ZnO thin film. The results could be useful for the further development of monolithic SAW devices.     

Silver nanoparticles deposited on porous silicon as a surface-enhanced Raman scattering (SERS) active substrate

Silver nanoparticles were deposited spontaneously from their aqueous solution on a porous silicon (PS) layer. The PS acts both as a reducing agent and as the substrate on which the nanoparticles nucleate. At higher silver ion concentrations, layers of nanoparticle aggregates were formed on the PS surface. The morphology of the metallic layers and their SERS activity were influenced by the concentrations of the silver ion solutions used for deposition. Raman measurements of rhodamine 6G (R6G) and crystal violet (CV) adsorbed on these surfaces showed remarkable enhancement of up to about 10 orders of magnitude.     

Covalent layer-by-layer assembly of redox active molecular multilayers on silicon (100) by photochemical thiol-ene chemistry

The fabrication of thin organic films covalently grafted onto silicon substrates is of significant interest, as they are expected to give access to a broad range of new materials for integration into microelectronic applications. Covalent layer-by-layer (LbL) assembly offers a high degree of freedom when designing such thin films. In this work an approach for the preparation of covalent redox active molecular multilayers on silicon (100) surfaces is presented using a highly branched decaallylferrocene and thiol-ene click chemistry. The multilayers are analyzed by ellipsometry, X-ray photoelectron sprectroscopy, and cyclic voltammetry. The results indicate that the multilayer growth is linear for at least sixteen layers and the density of ferrocenes per layer is in the range of 6 × 10?11 mol cm?2. Moreover, this method for LbL assembly is extended to surfaces which have been locally passivated by microcontact printing. By atomic force microscopy measurements it is possible to show that the covalent LbL deposition proceeds exclusively in the nonpassivated areas.     

Longwave generation in laser structures based on InGaAs(N) quantum wells on GaAs substrates

The MBE growth regime has been optimized for the obtaining of laser structures based on InGaAs(N)/GaAs quantum wells (QWs) with high indium content. Structures containing InGaAs and InGaAsN isolated QWs exhibit low-threshold longwave emission at room temperature. Lasers based on QWs of the In_0.35GaAs and In_0.35GaAsN_0.023 types are characterized by the radiation wavelengths λ=1.085 and 1.295 μm at a threshold current density of 60 and 350 A/cm², respectively.     

Effects of a ZnTe buffer layer on structural quality and morphology of CdTe epilayer grown on (001)GaAs by molecular beam epitaxy

The structural properties, crystalline quality and surface morphology of CdTe thin films without and with a ZnTe buffer layer grown on (001)GaAs by molecular beam epitaxy (MBE) have been studied. CdTe thin film directly prepared on GaAs substrate displays (111) orientation with an island growth mode, whereas the CdTe epilayers with a ZnTe buffer are (001)-oriented single-crystalline film with a two-dimensional (2D) growth mode. The morphology and surface root-mean-square (RMS) roughness of CdTe epilayers are also dramatically improved by using a ZnTe buffer. Furthermore, it is suggested that the high-temperature (HT) ZnTe buffer grown at 360 °C is more efficient for enhancing CdTe structural quality than the low-temperature (LT) one at 320 °C. The CdTe epilayer on the HT-ZnTe buffer shows a narrower full-width at half-maximum (FWHM) of double-crystal X-ray rocking curve (DCXRC) for (004) reflection and a smaller RMS roughness.     

Effect of Ca and buffer layers on the performance of organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum

The effects of buffer layers, including LiF, LiCl, NaF, NaCl, NaI, KI, RbF, RbCl, CsF, CsCl, MgF₂, CaF₂, BaF₂, and BaCl₂ on electron injection and device performance in organic light-emitting diodes based on tris-(8-hydroxyquinoline) aluminum, were investigated systematically. The insertion of the buffer layers at the organic/cathode interface not only reduced the operating voltage, but also enhanced the luminance and efficiency, which is attributed to the improvement of electron injection efficiency. It was found that the efficiency of the electron injection was closely related to the inherent properties of the buffer layer, such as its melting point (MP) and dielectric constant (ε), as well as with the buffer layer's interface with the metallic electrode through the effective work function (WF). Low MP, low ε and low WF values result in an effective improvement in the injection of the electrons, and thus to the device performance. The electroluminescent performance was further improved by the introduction of calcium between the buffer layer and the aluminum electrode.     

Noncovalent antibody immobilization on porous silicon combined with miniaturized solid-phase extraction (SPE) for array based immunoMALDI assays

This paper presents a new strategy to combine the power of antibody based capturing of target species in complex samples with the benefits of microfluidic reverse phase sample preparation on an integrated sample enrichment target (RP-ISET) and the analysis speed of MALDI MS. The immunoaffinity step is performed on an in-house developed 3D-structured high surface area porous silicon (PSi) matrix, which allows efficient antibody immobilization by surface adsorption without any coupling agents in 30-60 min. The hydrophilic nature of the porous silicon surface at the molecular level displays a low adsorption of background peptides when exposed to complex digests or plasma samples, improving the conditions for the antigen specific extraction and subsequent readout. At the same time, the hydrophobic behavior, due to the nanostructured surface, of the PSi material facilitates liquid confinement during the assay. Using a footprint conforming to the standard for 384 well microplates, direct adaption of the protocol into standard sample handling robots is possible. The performance of the proposed immunoaffinity PSi-ISET immunoMALDI (iMALDI) assay was evaluated by specific detection of angiotensin I at a 10 femtomol level in diluted plasma samples (10 μL, 1 nM).     

High-power low-threshold laser diodes (λ=0.94μm) based on MBE-grown In0.1Ga0.9As/AlGaAs/GaAs heterostructures

The parameters of high-power laser diodes operating at λ=0.94 μm, based on MBE-grown In_0.1Ga_0.9As/AlGaAs/GaAs quantum-dimensional heterostructures, are reported. The laser diodes manufactured using an optimized MBE technology and specially selected dopant profiles are characterized by a lowthreshold current density, a high optical output power, a high differential quantum efficiency, and a long working life (above 10000 h).     

Novel active heterogeneous Fenton system based on Fe3-xMxO4 (Fe, Co, Mn, Ni): the role of M2+ species on the reactivity towards H2O2 reactions

In this work, the effect of incorporation of M2+ species, i.e. Co2+, Mn2+ and Ni2+, into the magnetite structure to increase the reactivity towards H2O2 reactions was investigated. The following magnetites Fe3-xMnxO4, Fe3-xCoxO4 and Fe3-xNixO4 and the iron oxides Fe3O4, gamma-Fe2O3 and alpha-Fe2O3 were prepared and characterized by M?ssbauer spectroscopy, XRD, BET surface area, magnetization and chemical analyses. The obtained results showed that the M2+ species at the octahedral site in the magnetite strongly affects the reactivity towards H2O2, i.e. (i) the peroxide decomposition to O2 and (ii) the oxidation of organic molecules, such as the dye methylene blue and chlorobenzene in aqueous medium. Experiments with maghemite, gamma-Fe2O3 and hematite, alpha-Fe2O3, showed very low activities compared to Fe3O4, suggesting that the presence of Fe2+ in the oxide plays an important role for the activation of H2O2. The presence of Co or Mn in the magnetite structure produced a remarkable increase in the reactivity, whereas Ni inhibited the H2O2 reactions. The obtained results suggest a surface initiated reaction involving Msurf2+ (Fe, Co or Mn), producing HO radicals, which can lead to two competitive reactions, i.e. the decomposition of H2O2 or the oxidation of organics present in the aqueous medium. The unique effect of Co and Mn is discussed in terms of the thermodynamically favorable Cosurf3+ and Mnsurf3+ reduction by Femagnetite2+ regenerating the active species M2+.