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Potentiometric sensors based on semiconductor and metallic materials modified by electrochemical techniques are proposed. It is demonstrated that the electrochemical modification of the surface improves the electroanalytical properties of the electrodes. Nonmodified and modified electrodes are recommended for the potentiometric titration of iodides. Procedures are developed for the potentiometric determination of cyanide- and iodine-containing pesticides using GaAs- and Ti-electrodes. Keywords: potentiometric sensors, modified GaAs- and Ti-electrodes, electrode function, cyan- and iodinecontaining pesticides. DOI: 10.1134/S1061934811120033, One of the promising areas of analytical chemistry is the modification of the surface of chemical sensors for the variation of their properties. As a result of target mechanical, chemical, [...]

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.solener.2010.05.013 Byline: Kanglin Xiong (a)(b), Shulong Lu (b), Taofei Zhou (b), Desheng Jiang (a), Rongxin Wang (b), Kai Qiu (b), Jianrong Dong (b), Hui Yang (a)(b) Keywords: Internal quantum efficiency; Surface recombination; Genetic algorithm; Full spectra Abstract: To investigate factors limiting the performance of a GaAs solar cell, genetic algorithm is employed to fit the experimentally measured internal quantum efficiency (IQE) in the full spectra range. The device parameters such as diffusion lengths and surface recombination velocities are extracted. Electron beam induced current (EBIC) is performed in the base region of the cell with obtained diffusion length agreeing with the fit result. The advantage of genetic algorithm is illustrated. Author Affiliation: (a) Institute of Semiconductors, CAS, No. A35, Qing Hua East Road, Beijing 100083, PR China (b) Suzhou Institute of Nano-tech and Nano-bionics, CAS, Ruoshui Road 398, Suzhou 215125, PR China Article History: Received 25 January 2010; Revised 23 April 2010; Accepted 17 May 2010 Article Note: (miscellaneous) Communicated by: Associate Editor Takhir Razykov

A yttrium iron garnet/gadolinium gallium garnet-gallium arsenide (YIG/GGG-GaAs)-based magnetically-tunable wideband microwave band-pass filter with large tuning ranges for the center frequency (5.90-17.80 GHz) and the bandwidth (1.27-2.08 GHz) in the pass-band using a pair of cascaded band-stop filters is reported. The design and numerical simulation of the band-pass filter that incorporates multisegment microstrip meander-lines and 2-D nonuniform bias magnetic fields were first carried out using Ansoft High Frequency Structure Simulator (HFSS) software suite. The measured transmission characteristics of the band-pass filter at center frequency of 8.28 GHz, using 2-D nonuniform bias magnetic fields centered at 2,750 Oe and 4,150 Oe facilitated by Nd-Fe-B permanent magnets, shows a -3-dB bandwidth of 1.73 GHz, an out-of-band rejection of -33.5 dB, and an insertion loss of -4.2 dB. A good agreement between the simulation and experimental results for the band-pass filter in the center frequency and the bandwidths of the pass-band and the two guarding stop-bands has been accomplished. Index Terms--Bandpass filters, bandstop filters, ferromagnetic resonance (FMR), tunable filters, yttrium iron garnet (YIG) filters.

Hybrid spintronic structures, integrating half-metallic magnetic oxides and Heusler alloys with their predicted high spin polarization, are important for the development of second-generation spintronics with high-efficient spin injection. We have synthesized epitaxial magnetic oxide [Fe.sub.3][O.sub.4] on GaAs(100) and the unit cell of the [Fe.sub.3][O.sub.4] was found to be rotated by 45[degrees] to match the gallium arsenide GaAs. The films were found to have a bulk-like moment down to 3-4 nm and a low coercivity indicating a high-quality magnetic interface. The magnetization hysteresis loops of the ultrathin films are controlled by uniaxial magnetic anisotropy. The dynamic response of the sample shows a heavily damped precessional response to the applied field pulses. In the Heusler alloy system of [Co.sub.2] MnGa on GaAs, we found that the magnetic moment was reduced for thicknesses down to 10 nm, which may account for the lower than expected spin-injection efficiency from the spin-light-emitting diode structures. Using the element-specific technique of X-ray magnetic circular dichroism (XMCD), the reduced spin moments were found to originate from the Mn rather than the Co atoms, and the improvement of the interface is thus needed to increase the spin injection efficiency in this system. Further studies of the I--Vcharacteristics of [Fe.sub.3][O.sub.4]/GaAs(100) and [Fe.sub.3][O.sub.4]MgO/GaAs(100) show that the [Fe.sub.3][O.sub.4]-based spintronic structures have a well-defined Schottky or tunneling barrier of moderate barrier height, which is encouraging for high-efficient spin injection. Index Terms--Gallium arsenide (GaAs), Heusler alloys, magnetic oxides, magnetite, molecular-beam epitaxy, spintronics, ultra-thin films.

We characterize radiation induced defects in n-type GaAs following electron, proton, and silicon ion irradiations using Deep Level Transient Spectroscopy (DLTS) and Electron Beam Induced Current (EBIC) measurements. EBIC micrographs show the existence of radiation induced recombination centers following high energy proton (E > 50 MeV) or 22 MeV silicon ion irradiations, which were not observed following 1 MeV electron or 2 MeV proton irradiations. The evolution of the U-band defect as determined by DLTS seems to occur when active recombination centers are observed in the EBIC images and therefore, appears to be produced by high energy recoils probably creating defect clusters. Index Terms--Displacement damage, DLTS, EBIC, GaAs, heavy ion, irradiation, NIEL, photovoltaic, recoil spectrum, recombination center.

Photosensitive polybenzoxazole (PBO) film has been used in GaAs heterojunction bipolar transistor (HBT) technology for stress buffer and mechanical protection layer applications. However, this film needs to be cured at high temperatures for a long period of time in order to obtain its desired excellent material characteristics. High-temperature curing can result in degradation to the electrical characteristics and performance of the underlying GaAs devices due to limited thermal budget. In this paper, we have characterized the effects of curing the PBO film on GaAs HBT wafers using a conventional convection furnace and using a variable frequency microwave (VFM) furnace. The results show that a VFM cure can achieve similar excellent physical, mechanical, thermal, and chemical material characteristics at a lower curing temperature and in a much shorter time, as compared to convection furnace curing, therefore resulting in minimal GaAs device degradation. Based on these results, an optimum curing condition using the VFM method can be obtained that satisfies both stress buffer layer material and device requirements for GaAs HBT technology. Index Terms--Buffer layer, convection curing, GaAs, heterojunction bipolar transistor (HBT), polybenzoxazole (PBO), polymer, variable frequency microwave (VFM) curing.

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.

We have analyzed the electrical properties of both Si[O.sub.x] on InGaAs and Si[N.sub.x] on InGaAs, by utilizing a metal-insulator-semiconductor (MIS) structure. For improving film or interface quality, both oxide and nitride samples underwent furnace annealing (FA) in hydrogen at various temperatures. From the leakage current and capacitance characterization, we found that the electrical properties of the nitride samples such as leakage current, injected charges, and interface trap density are improved by FA, while on the contrary, the properties of the oxide samples are slightly deteriorated. The optimum annealing temperature for nitride samples is in the temperature range of ~ 400 to 450 [degrees] C. Also, by secondary ion mass spectroscopy (SIMS) analysis, we provide evidence of inter-diffusion occurring in the oxide samples after annealing.

Photon emission of gallium arsenide substrates in air was observed through the use of scanning tunneling microscopy. The tunneling topography of the substrates which were protected with a film of paraffin oil showed the stability of the tunneling current. Through the emission spectrum, the emitted lights can be ascribed to radiative recombinations which were excited by scanning tunneling microscopy. Results also revealed that surface modifications influenced the decay luminescence intensity of gallium arsenide surfaces.

The cathodoluminescence of the gallium arsenide and aluminum gallium arsenide quantum wells was analyzed through the use of wet oxidation and thermal annealing. The cathodoluminescence of these compounds had emitted from the regions of different oxidation and subsequent annealing temperatures. Monochromatic cathodoluminescence images of the quantum wells in oxide and nonoxide regions exhibited a dark gap spot which was the dead layer that originated from the lateral built-in field in the transition region.

Franz-Keldysh oscillations of piezoreflectance in a delta-doped gallium arsenide were studied through the application of fast Fourier transformations. The piezoreflectance of Franz-Keldysh oscillations and their fast Fourier transformations spectra were described by a model calculation which includes the energy gap modulation in a uniform electric field. Results revealed that Franz-Keldysh oscillations line shapes in the piezoreflectance had no distortions of the modulation electric field similar to the experiments about photoreflectance and electroreflectance.

An analysis was conducted to examine the energy structure and carrier excitation in self-assembled indium arsenide/gallium arsenide quantum dots at various resonant excitation conditions. Photoluminescence excitation spectroscopy and photoluminescence measurement were utilized. Results revealed that quantum dots whose upper transitions met the laser energy and the entire quantum dot ensemble were stimulated due to a two-photon absorption and excitation carriers. In turn, the relaxation mechanism of the indium arsenide self-assembled quantum dots was identified.

A model which can predict the measured blueshift for various levels of optical excitation for aluminum gallium arsenide based n-i-p-i structures was formulated. The logarithmic dependence of the optical blueshift and the excitation intensity was derived. Results revealed that the logarithm of the excitation light intensity and the proportionality constant obtained were in agreement. The exponential decline of carrier recombination lifetime in a n-i-p-i structure occurred when the excitation light intensity increased.

Shockley's standard model and Shockley and Quisser's detailed balance model for the diode are differentiated. The first one, which describes the monotical increase of the diode reverse saturation current with the device thickness. The detailed balance model, on the other hand, forecasts this current's saturation with increasing thickness. Furthermore, the standard model underestimates the computation of the limiting efficiency of solar cells. However, the differences diminish when the nonradiative recombination becomes significant.

The photoluminescence (PL) and PL excitation spectra of individual Er centers in GaAs:Er,O and AlGaAs:Er,O were measured by site-selective luminescence spectroscopy. Similarities in the spectra follow the similarities of the centers and became the bases for the grouping of the centers into different classes. A major part of the Er centers in GaAs which was formed under oxygen codoping contained two oxygen atoms and two arsenic atoms at the nearest-neighbor sites of the Er atom.

Gallium arsenide (GaAs) offers an attractive choice for room temperature X- and [Gamma]-ray detectors. However performance of SI LEC bulk GaAs detectors is at present limited by the short carrier lifetime and by the diode breakdown occurring as soon as the electric field reaches the back ohmic contact. We have shown that ohmic contacts based on ion implantation allowed us to go far beyond the bias voltage necessary to achieve a fully active detector. However the conventional thermal treatments (850 [degrees] C, 30 s) required to anneal the damage induced by ion implantation strongly reduces the charge carrier lifetime in the detector. Alenia S.p.A. has developed two improved processes (RA and RB) which avoid high temperature annealing and the consequent charge carrier lifetime reduction. With the new detectors, in pixel (200x200 [[[micro]meter].sup.2]) configuration, a charge collection efficiency (cce) of 90 % for 59.5 keV X-rays and a FWHM of 3.35 keV have been achieved at room temperature. These features, thickness, applied voltage, cce and FWHM are suitable for application of GaAs pixel detectors in medical imaging. Results obtained with [Alpha] particles and X-rays at different temperatures and in a wide range of applied bias in detectors made with standard, implanted and improved processes are presented, compared and discussed.

GaAs microbridge thermocouples with lengths ranging from 40 to 650 [[micro]meter] and operating at room temperature have been fabricated for the detection of infrared radiation. A C[O.sub.2] laser of a 10.6-[[micro]meter] wavelength was used to characterize the performance of the detectors in air and in vacuum. A responsivity of 4.2 V/W with a corresponding detectivity [D.sup.*] = 8 x [10.sup.6] cm [Hz.sup.1/2]/W and a time constant of 2.2 ms have been measured in vacuum for 650-[[micro]meter]-long bridges, and a shorter time constant of 50 [[micro]second] was obtained for 40-[[micro]meter]-long bridges. An analytic thermal transport model has been used to simulate the operation of the sensors. The heat-transfer coefficient has been evaluated by comparing the data from air and vacuum measurements. The spectral response and the absorbance of the microbridge have also been presented. [203] Index Terms - Gallium arsenide, heat transport, infrared detectors, thermocouple.

Soft X-ray photoelectron spectroscopic studies of the growth of GaF3 films on GaAs(110) upon XeF2 exposure at high temperature show that GaF3 films form on GaAs with an interface of GaF, elemental As and AsF at temperatures between 300 and 550 K. The initial F intake rate varies with substrate temperature, while changes are observed in the thickness and composition of the film-substrate interface. XeF2 etches GaAs above 550 K to cover the GaAs surface with just a monolayer of elemental As.

Analysis of the epitaxial growth of insulating BaF2 films on (100) and (111)-oriented GaAs substrates suggests that the (100)-oriented BaF2 deposited on (100) GaAs at low temperatures result in films with epitaxial reflection high-energy electron diffraction and three-dimensional growth. The epitaxial quality of the (100) films is influenced by temperature. The 111-oriented films show two-dimensional growth. Studies of the interface chemistry suggest the presence of a Ba state other than that of the BaF2.

Electron-beam evaporation and rapid thermal annealing at 400 to 500 degrees centigrade facilitate the reorganization of constituent elements in Pd/Ge contacts to n-type GaAs. The contact layer exhibits a gallium SIMS signal bump that is associated with good ohmic contact behavior. This shallow ohmic contact ability is used to develop GaAs/AlGaAs and GaAs/InGaAs/AlGaAs negative resistance field-effect transistors.

Investigations of the growth of erbium-doped GaAs layers during metalorganic vapor phase epitaxy reveal that the use of (t-butylcyclopentadienyl)3Er and (i-propylcyclopentadienyl)2cyclopentadienyl Er sources at relatively low Er bubbler temperature of 90 degrees Celsius leads to the controlled incorporation of optically active Er3+ into GaAs. Er doping shows superlinear rise with source mole fraction and is necessary refractory to growth temperature due to the low elemental vapor pressure of Er and low decomposition temperature of the Er source materials.

Structural analysis of ZnSe epilayers reveals that crystalline properties are degraded for layers grown beyond critical thickness. Atomic layer epitaxy facilitates the growth of the epilayers of GaAs (100) substrates. The elastic strain of the epilayers depends on layer depth near critical thickness.

Molecular beam epitaxy (MBE) is used to manufacture new ultrathin magnetic multilayers having ferromagnetic tau-MnAl with nonmagnetic NiAl. The multilayers are grown on GaAs substrates. The multilayers exhibit perpendicular magnetization, coercivity and remanent magnetization. The magnetic properties depend on the thickness of the NiAl layers.

The short-period superlattice (SPS) strained laser, which has a 1.07 micrometer lasing wavelength and a 130 A per centimeter squared threshold current density, is ideal to develop long wavelength lasers. The SPS laser, which does not alter the characteristic temperature of the long wavelength laser, possesses a SPS active layer, comprising InAs and GaAs.

Deep-level transient spectroscopy was employed in vapor-phase metalorganic epitaxially cultured GaAs:Sb to trace an EL5-like trap which probably results from a complex defect VGaAsi. The isoelectronic doping level with Sb and the V/III ratio are varied to understand the behavior of the EL5-like trap. Any rise in undoped material partial pressure results in a corresponding increase in the concentration of the EL5-trap while Sb doping results in a drop in the concentration.

The problem of acceptor neutralization in hydrogenated GaAs epilayers is studied. Experiments are performed wherein several samples of positive-type GaAs structures are epitaxially prepared and subsequently diffused with hydrogen. Second-mass ion spectrometry is then used to determine the hydrogenated structures' deuterium diffusion profiles. The active acceptor concentration and free-hole mobility before and after hydrogenation are also obtained. Results reveal the presence of hydrogen vibration modes which is a direct proof of the existence of hydrogen-acceptor complexes.

The temperature and lifetime of photoexcited electrons in semi-insulating GaAs wafers are investigated. Spectroscopic and photoluminescence measurements are performed on a laser-illuminated wafer to obtain the temperature of the structure's photoexcited electron gas. The correlation between the wafer's experimentally determined temperature and carrier lifetime is then numerically calculated. The resulting temperature and lifetime topography of the wafer is found to be very useful for the quantitative analysis of semiconductor substrates and epitaxial layers.

The misorientation and strain in GaAs/Si systems are investigated. GaAs epilayers grown in a molecular-beam-epitaxy system at 700 degrees centigrade are used as specimens. A modified Laue backreflection method is employed to obtain the correlation between the vicinal angle and the misorientation between GaAs and Si. X-ray double-crystal diffractometry is then performed on the GaAs/Si heterostructure systems. Results show that a small amount of shear stress and tensile stress caused by the large difference in the thermal-expansion coefficients of the twomaterials is present in the system.

An experiment was conducted to study platinum and GaAs substrates for amorphous phase formation and early crystalline reactions. High-resolution transmission electron microscopy (HRTEM) was used to examine thermally annealed semi-insulating gallium arsenide substrates. The crystalline reactions and amorphous phase formation were observed.

GaAs and AlGaAs double heterostructures were studied to assess the measurement of transient photoluminescence (TPL) and carrier recombination lifetimes. The experiment analyzed different TPL studies of recombination analysis, including computer simulation, the recombination effects model and recombination rate analysis model. Various measurements of incident optical intensities were necessary to define physical carrier lifetimes.

The 33GHz operation of a packaged divide-by-32/64 static prescaler designed for instrument applications is reported. The technology uses 0.1-micrometer enhancement- and depletion-mode MODFET's with psuedomorphic InGaAs channels defined by optical lithography and a self-limiting oxide-spacer technique. This operation demonstrates the fastest operation of a static divider circuit in FET technology.

A new GaAs based receiver substrate material, grown by molecular beam epitaxy on high resistivity silicon extends the total system bandwidth to 5 T-Hertz and increases the system sensitivity by a factor of 6. The carrier lifetime is short at 1.8 picoseconds, and allows fast sensitive detector switching when combined with the ion implanted silicon's high mobility and dark resistivity. The THz pulse passes through the substrate without losses due to the highly resistive silicon substrate.

Low pressure organometallic vapor phase epitaxy (LPOMVPE) was used with a liquid CCl4 source for carbon for the doping of p-GaAs substrates. Photoluminescence was used to study the band-gap shrinkage of the substrate. A hole concentration of more than 10 to the power 20 cm to the power -3 was obtained.