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An electrochemical method is proposed for the modification of the surface of semiconductor gallium arsenide sensors. The electrochemical modification of the surface of GaAs-electrodes leads to the improvement of their electrochemical characteristics: an increase in the slope of the electrode function, a decrease in response time, and the extension of the concentration range. Potentiometric titration using unmodified and modified GaAs-electrodes for the determination of chlorides with silver nitrate in soil has been performed. The application of the modified sensors ensures the detection of the titration end-point with a higher accuracy. Keywords: chemical sensors, electrochemically modified GaAs-electrodes, potentiometric titration, determination of chlorides in soil DOI: 10.1134/S1061934814110033, Chemical sensors are widely known and successfully used in potentiometry for environmental analytical monitoring, certification tests, and biochemical studies because of their high sensitivity, low cost, and simplicity of equipment. [...]

The band gaps of the two-dimensional photonic crystals, created by inhomogeneous triangular photonic crystal of variable central hexagonal holes are derived. The structure is made of air holes in GaAs. We present the best absolute photonic band gap for this structure by changing the holes' radii. The photonic band gaps are calculated by the plane wave expansion method. The results indicate 95% overlap in the band gaps of both polarizations of TE and TM in triangular lattice. PACS Nos: 74.62.Bf, 42.70.Qs, 71.10.Fd, 71.15.Ap Nous derivons les intervalles de bande (gaps) dans des cristaux photoniques a deux dimensions, crees a l'aide de cristaux photoniques triangulaires inhomogenes avec trous hexagonaux centraux variables. La structure est faite de trous d'air dans du GaAs. Nous presentons les meilleurs resultats d'intervalles de bande pour cette structure avec des trous de differents rayons. Nous calculons les intervalles de bande photoniques a l'aide de la methode d'expansion en ondes planes. Les resultats pour un reseau triangulaire indiquent un recouvrement de 95 % des deux polarisations, TE et TM, dans l'intervalle de bande. [Traduit par la Redaction], 1. Introduction Photonic crystals (PCs) are artificial structures composed of a periodic arrangement of dielectric material in one, two or three dimensions. The periods of these crystals are comparable to [...]

Local manipulation of electric fields at the atomic scale may enable new methods for quantum transport and creates new opportunities for field control of ferromagnetism and spin-based quantum information processing in semiconductors. We used a scanning tunneling microscope to position charged arsenic (As) vacancies in the gallium arsenide 110 [GaAs(110)] surface with atomic precision, thereby tuning the local electrostatic field experienced by single manganese (Mn) acceptors. The effects of this field are quantified by measuring the shift of an acceptor state within the band gap of GaAs. Experiments with varying tip-induced band-bending conditions suggest a large binding energy for surface-layer Mn, which is reduced by direct Coulomb repulsion when the As vacancy is moved nearby. 10.1126/science.1197434

Wideband 8-12-GHz inline-type microwave power sensors that are based on measuring the microwave power coupled from the coplanar waveguide line by a microelectromechanical systems membrane are presented. In this method, the signal is available during the power detection. In order to obtain the low reflection losses and insertion losses, as well as the wideband response of the power sensor, an impedance match structure and a compensating capacitance are proposed. The fabrication of the power sensor is compatible with the GaAs monolithic microwave integrated circuit (MMIC) process. The experimental results show that the sensor has reflection losses better than 20 dB and insertion losses less than 0.45 dB up to 12 GHz. A sensitivity of more than 30 [micro]V/mW and a resolution of 0.2 mW are obtained at the 10-GHz frequency. [2008-0219] Index Terms--GaAs, micromachining, microwave power sensor, monolithic microwave integrated circuits (MMICs).

We investigated the magnetic anisotropy of ultrathin bcc-Fe (001) films with a fcc-Au(001) cover layer, grown onto GaAs (001) (4 x 1) and (2 x 6)/(3 x 6) reconstructed surfaces. The magneto-optical Kerr effect hysteresis loops revealed existence of a strong in-plane uniaxial magnetic anisotropy in the Fe films grown on both the surfaces. Details of the in-plane uniaxial anisotropy ([K.sub.U]), cubic anisotropy ([K.sub.C]), and effective demagnetization field (4[pi][M.sub.eff]) were studied by Brillouin light scattering method. We observed a stronger reduction of [K.sub.U], [K.sub.C], and 4[pi][M.sub.eff] in thinner Fe layers (below 1.3 nm) grown on both the surfaces. In the case of Fe films grown on GaAs (4 x 1) surface, anisotropies observed were smaller than that for the (2 x 6)/(3 x 6) surface. This reflects the role of surface structure in determining the magnetic anisotropies. Index Terms--Brillouin light scattering, GaAs reconstruction, magnetic anisotropy, spin waves.

We measured the carrier concentration distribution of gradient-doped GaAs/GaAlAs epilayers grown by molecular beam epitaxy before and after annealing at 600[degrees]C, using electrochemical capacitance voltage profiling, to investigate the internal variation of transmission-mode GaAs photocathodes arising from the annealing process. The results show that the carrier concentration increased after annealing. As a result, the total band-bending energy in the gradient-doped GaAs emission layer increased by 25.24% after annealing, which improves the photoexcited electron movement toward the surface. On the other hand, the annealing process resulted in a worse carrier concentration discrepancy between the GaAs and the GaAlAs, which causes a lower back interface potential barrier, decreasing the amount of high-energy photoelectrons. OCIS codes: 160.2100, 250.0250.

Applying the concept of binary superimposed gratings, widely tunable single-mode laser diodes suitable for multispecies gas detection in the 1.8 [micro]m wavelength range could be manufactured on InAs/InGaAs quantum dash-in-a-well material. A discrete wavelength tuning range of 21 nm as well as continuous tuning over 0.8 nm are demonstrated. Water and hydrogen chloride could be detected at absorption lines 13 nm apart. OCIS codes: 140.3600, 280.3420.

In this paper the most recent advances on ferromagnetic resonance (FMR)-based wideband microwave band-stop and band-pass filters using flip-chip yttrium iron garnet (YIG)/gadolinium gallium garnet (GGG)- gallium arsenide (GaAs) layer structures are reported. Specifically, simultaneous enhancement in tunable bandwidths and peak absorption levels by utilizing the meander microstrip line with step-impedance low-pass filter design together with inhomogeneous magnetic field has been accomplished. For example, an ferromagnetic resonance absorption frequency tuning range of 5 to 21 GHz, an absorption level of -35.5 dB and a corresponding 3 dB absorption bandwidth as large as 1.70 GHz, centered at 20.3 GHz, have been accomplished with the band-stop filter. For the band-pass filter large tuning ranges for the center frequency (5.90-17.80 GHz), the pass-band bandwidth (1.27-2.08 GHz) as well as the two guarding stop-bandwidths (0.45-1.70 GHz), and an out-of-band rejection of -33.5 dB were demonstrated. A good agreement between the simulation and experimental results has been achieved. Finally, some desirable measurement data on the microwave power capability and the magnetic tuning speed of the filters has also been obtained. Index Terms--Bandpass filters, bandstop filters, ferromagnetic resonance, tunable YIG filters.

A first-principles plane-wave method with the ultrasoft pseudopotential scheme in the framework of density functional theory is performed to calculate the lattice parameters, the bulk modulus [B.sub.0] and its pressure derivative [B.sub.0]' of the zinc-blende GaAs (ZB-GaAs), rocksalt GaAs (RS-GaAs), CsCl-GaAs, NiAs-GaAs, and wurtzite GaAs (WZ-GaAs). We also calculate the phase transition pressures between different phases, Debye temperatures, and the anisotropies. Our results are consistent with other theoretical results. PACS Nos.: 62.20.Dc, 71.15.Mb Nous utilisons une methode fondamentale en ondes planes avec un pseudo-potentiel ultramou dans le cadre de la fonctionnelle de densite, afin de calculer les parametres de reseau, le module d'elasticite en volume [B.sub.0] et la derivee de pression de [B.sub.0]' de la blende GaAs (ZB-GaAs), du sel GaAs (RS-GaAs) et de la wurtzite GaAs (WZ-GaAs). Nous calculons egalement les pressions de transition entre differentes phases, les temperatures de Debye et les anisotropies. Nos resultats sont en accord avec d'autres resultats theoriques. [Traduit par la Redaction], 1. Introduction It is known that, elastic properties relate to various fundamental solid-state phenomena, such as inter-atomic potentials, equations of state, phonon spectra, and so on. Moreover, they are also [...]

This paper presents a production-oriented chip-set to be used as the circuitry needed to implement the necessary RF functionalities of a new generation of S-band satellite transponders for telemetry tacking and control (TT&C) applications. The RF hardware section integration is achieved by means of a customized chip-set of just four multi-chip multifunction MMIC (MCMM) modules. The functions contained in the monolithic microwave integrated circuits (MMICs) include the active circuits needed for the front-end low noise amplifier (LNA), the RF and IF converters, all the variable gain amplifiers (VGAs), the Voltage Controlled Oscillatar (VCO) for both transmit and receive sections, the frequency prescaler and multiplier needed to synthesize the frequency plan as well as the Local Oscillatar (LO) amplifiers. The selected technology is GaAs, mainly due to its radiation hardness, essential for aerospace applications, and good reliability. Issues such as suitable circuit topology, efficient dc biasing, circuit area minimization, cost-oriented system design and advanced packaging techniques have been addressed during the design. Measurements and yield results from the manufactured circuits will be presented showing that these components, even though especially designed in the frame of the GALILEO TT&C transponder predevelopment, are suitable for a variety of missions, from Deep space to near Earth, including spread-spectrum transponders with precision ranging function.

GaAs thin film has been grown on porous silicon by metal organic chemical vapour deposition (MOCVD) for different growth temperatures using atomic layer epitaxy (ALE) technique. The morphology of GaAs layer was investigated by atomic force microscopy (AFM). The effect of growth temperature is studied using photoluminescence measurements (PL).The photoluminescence spectra revealed a dissymmetry form toward high energies attributed to strain effect resulting from the lattice mismatch between GaAs and porous Si substrate. Keywords: GaAs, ALE technique, porous silicon, photoluminescence, INTRODUCTION The heteroepitaxy growth of GaAs on Si and porous Si substrates has received great interest due to its potential for the monolithic integration of GaAs, Si and hybrid devices [...]

This paper discusses and demonstrates the most popular sub-harmonic Gilbert mixers in 2-[micro]m GaInP/GaAs HBT technology. High two local oscillators (2LO)-to-RF isolation is important to alleviate the self-mixing problem of the sub-harmonic mixer. The demonstrated GaInP/GaAs HBT stacked-local oscillator (LO) mixer topology has achieved the best 2LO-to-RF isolation when compared with the previous literature. On the other hand, the leveled-LO sub-harmonic mixers have advantages in terms of the high speed and low dc supply voltage at the cost of much larger LO pumping power. Among all the structures, the bottom-LO sub-harmonic mixer has the lowest current consumption and the simplest circuit structure at the expense of the 2LO-to-RF isolation. Index Terms--DC offset, GaInP/GaAs HBT, Gilbert mixer, self-mixing, sub-harmonic mixer, two local oscillators (2LO)-to-RF isolation. Digital Object Identifier 10.1109/TMTT.2007.895169

A comprehensive study on the incorporation of As in a local area and its influence on the microstructures of wurtzite GaN grown by rf-plasma-assisted molecular-beam epitaxy are presented. The result reveal a significantly large tendency of As surface segregation with the surface segregation coefficient R~0.99, which indicates the difficulties to incorporate As into GaN, and thus to grow the ternary GaNAs alloys.

A spinodal decomposition range of the low N-content Al(sub x)Ga(sub 1-x)N(sub y)As(1-y) alloys grown on GaAs(001) is discussed. Transformations of the bonds and coherency strain energy appear when the phase separation decreases dramatically the spinodal decomposition range.

A new method for engineering the stoichiometric Gallium Arsenide surfaces with self-assembled monolayers of 4-mercaptobiphenyl is proposed. The result shows that the chemical modification of GaAs surfaces has a large potential for the flexible functionalization of GaAs-based semiconductor nanostructures with bio-organic molecular assemblies both in air and aqueous electrolytes.

High-temperature annealing of gallium arsenide in vacuum causes excess evaporation of arsenic, with accumulation of gallium as liquid droplets on the surface. Using real-time in situ surface electron microscopy, we found that these droplets spontaneously run across the crystal surface. Running droplets have been seen in many systems, but they typically require special surface preparation or gradient forces. In contrast, we show that noncongruent evaporation automatically provides a driving force for running droplets. The motion is predicted and observed to slow and stop near a characteristic temperature, with the speed increasing both below and above this temperature. The same behavior is expected to occur during the evaporation of similar III-V semiconductors such as indium arsenide.

An in-depth model is developed for the transient behavior of metal atoms adsorbed on the surface of GaN. The suggested model has helped in understanding the surface kinetics of GaN, has provided an indirect method of monitoring the kinetic evolution of these surfaces, and has introduced a novel method of in situ growth rate determination.

Fe films with the different thicknesses are grown on c(4*4) reconstructed GaAs (001) surfaces at low temperature by molecular-beam epitaxy and the in-plane uniaxial magnetic anisotropy is determined. The studies have shown that magnetic anisotropy is not affected after in situ annealing, but in-pla ne strain is completely changed.

The formation of well-ordered chains of InP quantum dots on GaAs (001) substrates is studied by using self-organized [In.sub.0.48][Ga.sub.0.52]P surface undulations as a template. The regions of increased In content and consequent increased strain have acted as a template for subsequent InP quantum dot growth and when the buffer layer is grown at lower temperatures, the undulations have not formed and the InP quantum dots have not shown any ordering.

The electrostatic potential distribution in AlGaAs/GaAs heterostructure with double split gates on the surface is studied. The results are obtained from the self-consistent solution of the three dimensional Schrodinger-Poisson equation and have shown that the quantized plateau accuracy is about [10.sup.-5]-[10.sup.-4] within the minimum slope of the current plateau.

A procedure is described for preparing high transmissive superconducting (S) contacts by diffusing indium into GaAs/[Al.sub.x][Ga.sub.1-x]As based high-mobility two-dimensional electron gas (2DEG). The low dimensional nature of the localized indium filament is characterized by phase slip centers in the I(V) curve of a shunted S/2DEG/S junction.

High resolution x-ray diffraction and deep level transient spectroscopy (DLTS) are used for studying multi-quantum-well (MQW) GaN/InGaN p-n junctions grown on epitaxial laterally overgrown (ELOG) n-GaN platform layers. Microcathodoluminescence spectra have shown a redshift luminescence in the laterally grown ELOG wings and modeling based on solving Poisson-Schroedinger equations have shown that the main reason for the redshift is the higher indium content in the wings.

Free-electron concentration and mobility of free-standing GaN nanowires (NWs) are determined by line shape analysis of the coupled longitudinal optical phonon-plasmon Raman modes (L+). Asymmetric broadening seen at the lower frequency side of the L+ phonon peak is attributed to the increase in surface optical modes due to the high surface-to-volume ratio of NWs.

Large-scale ab initio molecular dynamics method is used for determining the threshold displacement energies [E.sub.d] along five specific directions and to determine the defect configuration created during low energy events. The N defects created at low energy events along different crystallographic directions have a similar configuration like N-N dumbbell configuration, but various configurations for Ga defects are formed in GaN.

The coherence properties of interband and intraband optical transitions in self assembled InAs/GaAs quantum dots are described. The studies have shown that the electron-phonon interactions have played a role on the optical response of quantum dots and they have also stressed the primary role of the close environment on the coherence characteristics of quantum dots.

Stress is used for creating a harmonic potential for polaritons in GaAs microcavities and the results are presented for both trapped conditions and resonant, nontrapped conditions in the same sample. The transition at lower density is identified as a type of nonequilibrium Bose-Einstein condensation.

Single lateral InGaAs quantum dot molecules are embedded in a planar microcavity in order to enhance the luminescence extraction efficiency and a combination of metal-organic vapor phase and molecular beam epitaxy samples are produced that has displayed an enhanced single-photon emission rate. The presence of a polarization fine structure splitting of the molecular neutral excitonic states has led to two polarization split classically correlated biexciton-exciton cascades.

Relaxation of compressed InP and InGaAs at different strains and temperatures was investigated. It was observed that InP and InGaAs layers relax in three possible regimes, low-mismatch, high-mismatch and medium-misfit, which depend on the strain state of the film.

Low temperature InGaP (LT-InGaP) grown lattice match to GaAs was considered as a source of defects for implementation of quantum well intermixing (QWI) in an InGaAs QW structure grown on GaAs, such that the barrier-QW compositional change consists solely of a group III change of a group V Change. Such a feature allows for the identification of the sublattice responsible for the QWI.

The optical properties of lowly strained [In.sub.x][Ga.sub.1-x]As/GaAs quantum dots (QDs) samples grown by solid source molecular beam epitaxy (MBE) with indium contents of about 30% are investigated. The absorption character of optical transitions has helped in determining the wetting layer (WL) thickness in such a lowly strained [In.sub.0.3][Ga.sub.0.7]As/GaAs QD structure in a contactless and nondestructive manner and showing how it is altered by small indium content changes.

The effects of interdiffusion and its technological parameters on the subband structure in compressively strained InGaAsP quantum wells (QWs) using photoreflectance and photoluminescence techniques are investigated. It is found that QW intermixing does not influence the built-in electric fields distribution.

The effect of the shape anisotropy on the magnetic domain configurations of a ferromagnetic semiconductor (Ga, Mn)As/GaAs(001) epitaxial wire as a function of temperature is studied. The effect of the shape anisotropy on the magnetic domain configuration is relatively enhanced with increasing temperature since the intrinsic anisotropy is found to show stronger temperature dependence than the shape anisotropy.

A phenomenological methodology is applied to characterize the intrinsic diffusion of tin in GaAs based on the coupled motion of substantial and interstitial Sn atoms. Temperature and concentration gradients together with the available open-volume spaces, such as vacancy defects, control the diffusion process and the quantitative fits to annealing treatments performed at different temperatures are used to determine the activation energies and preexponential factors.

An investigation is carried out about [H.sub.2]S adsorption and dissociation on the gallium-rich GaAs(001)-4 x 2 surface by using hybrid density functional theory. The calculation results show that transfer of one H atom from the chemisorbed [H.sub.2]S to a second-layer As atom, with an activation barrier of 8.2 kcal/mol, is more kinetically favorable than insertion of an H atom into the Ga dimer bond or transfer of one H atom to the other Ga dangling bonds.

Monocrystalline Fe(001) films and Fe/Si/Fe(001) trilayers are grown by ion-beam sputter epitaxy on GaAs(001) and MgO(001) substrates and their magnetic properties are investigated by magnetic-optical Kerr effect and ferromagnetic resonance. The results of epitaxially sputtered substrate/Fe/Si/Fe systems with strong antiferromagnetic interlayer exchange coupling are shown as a demonstration of the good film and interface quality.

Magnetotransport measurements are used to study the magnetization reversal processes of in-plane magnetized (Ga,Mn)As epilayers with different hole concentrations in out-of-plane magnetic fields. The results show that the balance of (100) cubic magnetocrystalline anisotropy and uniaxial [110] anisotropy provides an understanding of the difference in the out-of-plane magnetization processes of (Ga,Mn)As epilayers.

A model is developed for the energy-dependent lifetime, which allows calculation of the temperature-dependent mobility spectrum of all types of carriers used in the neutrality equation, and applied to two n-GaAs/SI-GaAs epitaxial layers containing two types of carriers. The numerical solution of the neutrality equation, which contains all sources of charges present in the sample, and the integration of the total relaxation times are presented, so that it is possible to obtain the mobility of the partial charges and their part in the whole conductivity of the layer.

An experiment was conducted to study the temperature dependence of the coupling between n-type delta-doping regions. It was demonstrated that at room temperature the main coupling mechanism between an n-type delta-doping region and an adjacent plane of dots is energy-conserving electron-electron scattering, in which a hot electron in the delta-doping region transfers energy to a deeply confined electron in that region and relaxes to the quantum dot.

Long chains of quantum dots formed in InGaAs/GaAs(100) multiple layers were investigated by scanning electron, transmission electron, and atomic force microscopies. A one-dimensional postwetting layer was seen accompanying InGaAs/GaAs(100) quantum dot chains and this one-dimensional postwetting layer forms during the GaAs capping as the result of anisotropic In transportation away from the existing quantum dots.

The magnetization in the arrays of submicrometer-size disks fabricated from an epitaxial Fe layer grown on GaAs(001) is investigated. The Fe disks having a layer thickness of 20 nm undergo a transition between multiple and single magnetic domains when their diameter is about 100 nm.

The electronic structure of Si-doped In(sub y)Ga(sub 1-y)As(sub 1-x)N(sub x) films on GaAs substrates, grown by nitrogen-plasma-assisted molecular-beam epitaxy is examined by photoreflectance (PR) spectroscopy at temperatures between 20 and 300 K. The films are approximately 0.5 mum thick and had nitrogen mole fraction between x=0.0014 and x=0.0012, measured indirectly by a secondary-ion mass spectrometry calibration.

The low-frequency noise is studied in different AlGaAs/GaAs heterostructures under electric biases as a function of the temperature. The heterostructures differ in the two-dimensional electron-gas density and the mobility.

A series of lattice-matched In(sub x)Ga(sub 1-x)As/InAs(sub y)P(sub 1-y) double heterostructures with indium concentrations ranging between x=0.53 and x=0.78 is investigated. The double heterostructures incorporating indium-rich alloys experience lattice mismatch relative to the InP substrate.

Wafer bonding and hydrogen implantation exfoliation was used to fabricated a thin InP template layer on GaAs with intermediate silicon nitride bonding layers. This template layer was used to directly compare subsequent metal organic vapor phase epitaxial growth of InGaAs/ InAlAs quantum-well structures on these wafer-bonded templates to growth on a standard InP substrate.

The study is conducted, compared with calculations using Monte Carlo-modeling simulations and with experimental measurements. The results obtained using the nonlinear quantum kinetic theory, with those of Monte Carlo calculations and experimental data is remarkably good, thus satisfactorily validating the powerful, concise, and physically sound formalism.

The study is conducted, compared with calculations using Monte Carlo-modeling simulations and with experimental measurements. The results obtained using the nonlinear quantum kinetic theory, with those of Monte Carlo calculations and experimental data is remarkably good, thus satisfactorily validating the powerful, concise, and physically sound formalism.

The energy band structures and optical properties of highly strained dipole delta-doped In(sub 0.3)Ga(sub 0.7)As/GaAs single quantum wells were studied. The induced electric field across the quantum wells (QW) results in red shift of the interband transition and the spatial separation of confined electrons and holes by the Stark effect and under very high doping levels, the electrons and holes are confined in the delta-doped regions rather than in the QW, causing reduction of the wave-function overlap.

The effect of structure and strain on the etching process of epitaxial MnAs films on GaAs(001) is determined. It is found that the formation of cracks is accompanied by a strain release, which has a strong influence on the magnetic properties and reflects itself in an elevated phase-transition temperature compared to the uncracked film.

The effects of relaxation on the carrier distribution and emission in the quantum dots (QDs) and neighboring GaAs bottom layer are investigated by admittance and deep-level transient spectroscopy (DLTS). The energy difference between the two relaxation traps is comparable to the QD ground-state energy relative to the GaAs conduction-band edge, indicating that the traps might be the same trap that is pinned to the GaAs conduction band.