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BaTiO3 nanopowder was synthesized at low temperature by using an alkoxide-hydroxide sol-gel method and were sintered by microwave processing. Microwave sintering of BaTiO3 was carried out at different temperatures for 20 min to get dense ceramics. The phases, morphologies, crystal structures and weight losses of the synthesized and sintered materials were characterized by using X-ray diffraction (XRD), Field-emission scanning electron microscope (FE-SEM), Raman spectroscopy and Thermo-gravimetric analyzer (TGA). The materials could only be sintered densely at lower temperatures (1050–1150 °C). Enhancements of the dielectric constant (ɛ r ∼ 3500 at 100 kHz) and the remnant polarization (P r ∼ 6.90 μc/cm2) were found for BaTiO3 microwave-sintered at 1150 °C, which values were higher than those obtained by the conventional sintering. P-E loops confirmed the better ferroelectric nature of the microwave-sintered BaTiO3.

Tantalum-substituted Bi4Ti3O12 (Bi4Ti3-x/5Tax/5O12, BTTO) thin films were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by sol–gel technology. The effects of various processing parameters, including Ta content (x=0∼0.08) and annealing temperature (500∼800 °C), on the growth and properties of thin films were investigated. X-ray diffraction analysis shows that the BTTO thin films have a bismuth-layered perovskite structure with preferred (117) orientation. With the increase of Ta content, the grain size of film decreased slightly, and highly (117)-oriented BTTO films were obtained in the composition of x=0.06. Ta doping on the B-site of Bi4Ti3O12 could induce the distortion of oxygen octahedral and decrease the oxygen vacancy concentration by a compensating effect. The highly (117)-oriented BTTO thin films with x=0.06 exhibits the maximum remanent polarization (2Pr) of 50 μC/cm2 and a low coercive field (2Ec) of 104 kV/cm, fatigue free characteristics up to ≧ 108 switching cycles.

The Bi0.85 Eu0.15 FeO3 /Bi3.2 Y0.8 Ti3 O12 bilayer thin films were prepared on Pt(111)/Ti/SiO 2/Si(100) substrates using the sol-gel process and annealed by rapid thermal annealing in various annealing environments (ambient atmosphere and oxygen). The multiferroic/ferroelectric bilayer thin films were composed of 0.8-μ m thickness Bi0.85 Eu0.15 FeO3 and 0.2-μ m thickness of Bi3.2 Y0.8 Ti3 O12 thin film. The effects of annealing atmospheres (ambient atmosphere and oxygen) on the growth and properties of thin films were investigated. The results show that the intensities of the (117) diffraction peak of Bi3.2Y0.8Ti3O 12 film and (110) diffraction peak of Bi0.85Eu0.15FeO3 annealed in oxygen is stronger than those annealed in an ambient atmosphere. The Bi0.85Eu0.15FeO3/Bi3.2Y0.8Ti3O12 bilayer thin films annealed in the oxygen atmosphere exhibit the maximum remanent polarization (2\mbi Pr) and remnant magnetization (2Mr) of 26 μ C/cm2 and 3.44 emu/g, respectively. The improved magnetic and ferroelectric properties can be attributed to the elimination of defects, such as oxygen vacancy and vacancy complexes.

We have investigated optical properties and electrical properties of electrically degraded ZnSe layers by heavy Al doping, where their electron concentrations lie in the range of 7×1017–6×1018cm−3. Low-temperature photoluminescence exhibits two dominant radiative trap centers of 1.97eV (RD1) and 2.25eV (RD2), which are ascribed to VZn-related complex defects. Deep-level-transient spectroscopy shows two electron-trap centers at 0.16eV (ND1) and 0.80eV (ND2) below the conduction-band minimum. On the other hand, it is found that RD2 is dominant in relatively lightly doped ZnSe:Al layers below 7×1018cm−3 and RD1 is dominant in more heavily doped layers near 1×1019cm−3, while ND1 and ND2 are independent of Al doping concentration and their trap densities are estimated be below 3×1016cm−3. This indicates that RD1 and RD2 cause the carrier compensation in heavily doped ZnSe:Al layers. Their electron transport mechanism can be explained by ionized-impurity scattering mechanism.

Plasma sprayed coatings have been widely applied in modifying surface properties of metal components. It is also useful to prevent various types of wear, corrosion, erosion and thermal. But the residual stress is still an important problem which can effect the properties of sprayed coating. So it’s necessary to find out the reason of residual stress and the relationship between plasma sprayed condition and residual stress. Plasma spray coating layers with conventional ZrO2 powder was examined to calculate residual stress by X-ray diffraction method with various coating thickness.

Dielectric and piezoelectric properties of grain oriented (Bi0.5Na0.5)TiO3-BaTiO3 ceramics were investigated in a process that the templated grain growth and hot pressing methods were employed. A ceramic composition in Bi-based perovskite structure family, (Bi0.5Na0.5)TiO3-BaTiO3, was chosen as a matrix material and plate shaped SrTiO3 as a template. To examine the combined process effect on piezoelectric properties, three processes, conventional solid reaction, templated grain growth and the combine treatment of templated grain growth and hot-pressing, were compared. Specimen processed by templated grain growth and hot pressing methods exhibited better piezoelectric coefficient, d 31 (−79.6 pC/N) and electromechanical coefficient, k 33 (0.35) than those of the other specimens, fabricated by solid reaction and templated grain growth, respectively. The improved properties were attributed to reduction of pore existing in matrix, which is related to abnormal grain growth from SrTiO3 template and its resultant heterogeneous shrinkage.

The objective of this study is to investigate sintering behavior of silver/palladium electrode powders with TiO 2 nano-particle addition and their matching characteristics to a piezoelectric ceramics, Pb(Zr, Ti)O 3 . The electro-mechanical properties of the piezoelectric multilayer devices with the silver-TiO 2 particle electrode was studied. The densification of the electrodes was investigated as a function of sintering temperature and the reaction between the ceramic matrix and electrodes was studied by employing mechanical bonding test and scanning electron microscopy. The densification of the nanoparticle TiO 2 -added electrode paste followed the TiO 2 solid state diffusion-controlled mechanism upon sintering process. Reaction between ceramic and electrode layers with the TiO 2 nano-particle powder allows internal stress to be reduced and mechanical bonding strength to be increased. High adhesive strength and good electrical conductivity of more than 10 4 /Ω cm could be obtained in the multilayer ferr...

Ferroelectric Ba 0.7 Sr 0.3 TiO 3 (BST) thin films with/without Cr-dopant have been fabricated on Pt(111)/Ti/SiO 2 /Si(100) substrates using wet chemical deposition. From atomic force microscope analysis, it has been found that the average grain sizes of the films increase from 10.7 to 29.2 nm with increasing Cr content from 0 to 5 mol%. Dielectric constant tunability of the 5 mol% Cr-doped BST thin film has been measured to be 56.1% with a dc bias field of 267 kV/cm, which is larger than 26.3% for the undoped BST thin film. Furthermore, the 5 mol% Cr-doped BST film exhibits hysteresis characteristics with the remanent polarization (2 P r ) of 6 μC/cm 2 and the coercive field (2 E c ) of 40 kV/cm with a dc bias field of 230 kV/cm. The leakage current densities of the Cr-doped BST thin films are approximately 1 order of magnitude lower than that of the undoped BST thin film. The improved ferroelectric properties were attributed to the increased grain size and defect dipoles in the BST film by means of acceptor (Cr) doping.

We report on the ferroelectric properties of Bi 3.54 Nd 0.46 Ti 3 O 12 (BNT) thin films fabricated on Pt(111)/Ti/SiO 2 /Si substrates by a sol-gel process. The measured XRD patterns and SEM and TEM micrographs revealed that the films showed only a Bi 4 Ti 3 O 12 -type phase with random orientations. The Au/BNT/Pt capacitors showed excellent ferroelectric properties. For the film capacitor annealed at 700°C, the remanent polarization (2P r ) and the coercive field (2E c ) were 67 μC/cm 2 and 183 kV/cm at applied electric field of 300 kV/cm, respectively. Furthermore, the Au/BNT/Pt capacitor did not show any significant fatigue up to 1.5 × 10 10 read/write switching cycles at a frequency of 1 MHz.

Using deep-level-transient spectroscopy, we have investigated deep levels in heavily Al-doped ZnSe layers grown by molecular-beam epitaxy. The Al concentration of the ZnSe layers lies in the range of 5×1018–9×1018cm−3. The ZnSe:Al layers exhibit two electron-trap centers with the thermal activation energies of 0.16eV (ND1) and 0.80eV (ND2). ND2 is a dominant trap center with a trap density of 3×1016cm−3, while the trap density of ND1 is estimated to be 2×1015cm−3. However, ND2 shows anomalous behaviors, different from isolated point defects, in the following points: (1) the emission peak of ND2 moves to the low temperature side with increasing filling pulse duration; (2) the emission peak of ND2 is broader than theoretically calculated one for an isolated point defect; and (3) the capacitance-transient curve is nonexponential. It is observed by high-resolution x-ray diffraction that heavy Al doping results in the relaxation and plastic deformation of the ZnSe lattice. These behaviors can be ascribed to ex...

This article demonstrates that interdiffusion, which is inherent in heteroepitaxy, can be well suppressed by inserting a thin buffer layer grown at sufficiently lower temperature with taking a ZnSe/GaAs heteroepitaxy as an example. Two types of samples are prepared by molecular beam epitaxy (MBE): a 1114 A thick ZnSe epilayer grown on a 150 A thick low-temperature ZnSe buffer layer on a GaAs (0 0 1) substrate, and a 1356 A thick ZnSe layer grown directly on GaAs. The composition profile at the heterointerface measured by secondary ion mass spectrometry (SIMS) clearly shows that the Ga diffusion is greatly suppressed in the ZnSe/GaAs system prepared with the low-temperature buffer layers, while considerable Ga interdiffusion from the GaAs substrate into the ZnSe epilayer is observed in the sample without the low-temperature buffer layer. The suppression of interdiffusion is also evidenced by low-temperature photoluminescence (PL) spectroscopy which shows no trace of donor–acceptor pair (DAP) emission at around 2.7 eV normally observed in ZnSe epilayers. In addition to the suppression of interdiffusion, Se reaction with GaAs surfaces is suppressed, which leads to the reduction of built-in defect generation due to heterovalency. Consequently, the ZnSe layer grown on a thin low-temperature ZnSe buffer layer shows high crystallinity as indicated by strong and sharp exciton emission in low-temperature photoluminescence spectrum and narrow X-ray line width.

We propose ZnSe/BeTe:N superlattice (SL) as a new p-type cladding layer with improved p-type dopability, in which nitrogen-doped BeTe (N-doped) layers are inserted into undoped ZnSe layers. We have optimized the growth temperature for ZnSe/BeTe:N SLs. Both equivalent beam pressure (BEP) ratio and growth rate are further optimized in low-temperature growth of BeTe:N layers. The structural properties of BeTe:N layers were analyzed by reflection high-energy electron diffraction and high-resolution X-ray diffraction. Electrical properties were evaluated by the van der Pauw method and capacitance–voltage ( C – V ) measurements. We achieve the net acceptor concentrations of 1.2×10 19 cm −3 at the growth temperature of 350°C, BEP ratio of around 6, and growth rate of 35 nm/h.

We investigated the characteristics of deep levels in heavily Al-doped ZnSe layers grown by molecular beam epitaxy, whose electron concentration is saturated. Low-temperature photoluminescence showed deep level emission around 2.25 eV, and its intensity increases with Al concentration. This deep-level is located at 0.55 eV above valence band maximum, implying a point defect such as a self-activated center, AlZnVZn. Deep-level transient spectroscopy was used to investigate non-radiative trap centers in Al-doped ZnSe layers, and showed the presence of two electron trap centers at depths of 0.16 and 0.80 eV below conduction band minimum, with the electron capture cross-sections of 810−12 and 1×10−7 cm2, respectively. It is suggested the carrier compensation in heavily Al-doped ZnSe layers be ascribed to the deep levels.

We proposed a vertically integrated one-chip-two-wavelength light source which consists of a separate confinement single-quantum-well (SCH-SQW) ZnCdSe/ZnSe/ZnMgBeSe heterostructure for blue–green light emitters grown on SCH-MQW InGaP/InGaAlP for red light-emitting devices. We investigated, firstly, the effect of a thin low-temperature-grown ZnSe buffer layers (LT-ZnSe) in improving ZnSe crystallinity by inserting it between the high-temperature-grown ZnSe epilayer and the GaAs substrate, secondly, the growth optimization of LT-ZnSe on tilted GaAs (0 0 1) substrate, and lastly, the molecular beam epitaxy growth and characterization of ZnCdSe/ZnSe/ZnMgBeSe quantum well structures on metal organic chemical vapor deposition (MOCVD) grown III–V red light emitters. Optically pumped lasing is achieved from II–VI and III–V laser structures on one chip at room temperature. The present results clearly show the feasibility of epitaxial integration of II–VI and III–V laser structures.

The changes of magnetic properties with annealing temperature were studied in the amorphous Fe 86.7 Zr 3.3 B 4 Ag 6 thin film. The thin films were deposited by a DC magnetron sputtering method, annealed at 300–700°C for 1 h in vacuum under a field of 1.5 kOe parallel to the film plane, and then furnace-cooled. As a result, it has been found that the Ag addition to Fe–Zr–B amorphous thin films resulted in the decrease of crystallization temperature to 400°C due to promoted crystallization ability. Also, it gave rise to formation of fine BCC α-Fe crystalline precipitates with a grain size smaller than 10 nm in the amorphous matrix near 400°C, and led to prominent enhancement in the magnetic properties of the Fe 86.7 Zr 3.3 B 4 Ag 6 thin films. Significantly, excellent magnetic properties such as a saturation magnetization of 1.7 T, a coercive force of 1 Oe and a permeability of 7800 at 50 MHz were obtained in the amorphous Fe 86.7 Zr 3.3 B 4 Ag 6 thin film containing 7.2 nm-size BCC α-Fe, which was annealed at 400°C. Also, core loss of 1.4 W cm −3 ( B m =0.1 T) at 1 MHz in the thin film was obtained, and it is a much lower value than had been obtained in any existing soft magnetic materials. Such excellent properties are inferred to originate from the uniform dispersion of nano-size BCC α-Fe in the amorphous matrix.

This article demonstrates the effect of the thin low-temperature-grown ZnSe buffer layer (LT-ZnSe) in improving crystallinity of ZnSe-based films grown on GaAs substrate. Especially, the density of stacking fault defects, which is normally observed in ZnSe-based films grown on GaAs substrate, can be well reduced by inserting a thin ZnSe buffer layer grown at sufficiently low temperature between ZnSe/GaAs heterostructure. A ZnSe film with stacking fault densities as low as ∼2×10 6 /cm 2 was obtained by growing on the LT-ZnSe/GaAs buffer layers, in contrast, ∼8×10 8 /cm 2 was obtained by directly growing on GaAs substrate. The Frank-type stacking faults was dominant for films grown with LT-ZnSe, meanwhile, Shockley-type stacking faults was dominant for films grown without LT-ZnSe buffer. At the initial stages of ZnSe growth, three-dimensional growth mode is considerably suppressed with LT-ZnSe buffer. The improvement of crystallinity in the ZnSe film with LT-ZnSe and GaAs buffer is also evidenced by low-temperature photoluminescence spectroscopy and high-resolution X-ray diffraction, which show very large intensity ratio of near-band-edge emission to deep level emission and narrow X-ray diffraction peak width of (0 0 4) rocking curve with 92 arcsec, respectively.

La0.7Ca0.3MnO3 powders were prepared by both the solution combustion method and the solid state reaction method and were calcinated at various calcination temperatures and time intervals in air atmosphere. In the solid state reaction method, single-phase La0.7Ca0.3MnO3 was obtained after heat treatment of the powder at 1000°C for 24 hr. In the solution combustion method, however, single-phase La0.7Ca0.3MnO3 powder could be obtained easily when the powder was heat-treated at 650°C for only 30 min. Polycrystalline La0.7Ca0.3MnO3 powder, using the solution combustion method, showed good powder characteristics, such as an average grain size of 50 nm and a specific surface area of 92 m2/g. The resistance as a function of temperature and the magnetoresistance ratio in La0.7Ca0.3MnO3 thin films were attempted to examine the colossal magnetoresistance characteristics. These thin films also showed excellent colossal magnetoresistance properties in that 96% of the maximum magnetoresistance ratio was obtained at 97K.

We have investigated the ZnTe-based material system for the application to light-emitting devices. To this end, ZnTe homoepitaxy techniques have been developed to grow high-quality epitaxial layers. The conductivity control of ZnTe and ZnMgSeTe layers have been investigated. High structural quality n-type ZnTe layers with high carrier concentration are achieved by aluminum doping. Ambipolar conductivity control of quaternary layers is achieved. Aluminum doped ZnMgSeTe layers show a net carrier concentration of 5 × 10 16 cm -3 , while a high hole concentration of 2.5 x 10 19 cm -3 is achieved by p-type doping using a nitrogen plasma source. Based on those results, Zn 1-x Cd x Te/ZnMgSeTe triple-quantum-well(TQW) LED structures were fabricated. Bright electroluminescence was obtained at room temperature at the wavelength of 604 nm from Zn 0.7 Cd 0.3 Te and at 566 nm from Zn 0.85 Cd 0.15 Te TQW-LED.

Two types of double rectangular spiral thin-film inductors with a multi-layer structure of magnetic film/conduction film/magnetic film were fabricated using a Fe86.7Zr3.3B4Ag6 thin film with high permeability and resistance, in which easy axis of magnetization of the thin-film was perpendicular or parallel to the current direction. The dependence of inductance and resonance frequency on the inductor type indicated that the perpendicular geometry inductor has higher inductance than the parallel geometry one, because spins of magnetic film align more easily along the field direction due to higher field intensity in the perpendicular geometry. However, the increase of the inductance, resulted in the decrease of resonance frequency. Then the effects of permeability of the magnetic film on inductance and resistance of the perpendicular geometry inductor were investigated. The permeability was controlled by annealing the film at different temperatures. With increasing the permeability, the inductance increased, but the resistance also increased due to the increase in magnetic core loss. As the resonance frequency was higher in air-core inductor than in magnetic thin-film core inductor, it is suggested to increase the resonance frequency which is characteristic of the air-core inductor rather than magnetic properties of the magnetic thin-film should be enhanced.

A microstructural study of DC-sputtered Fe93−xZr3B4Agx films on Si(0 0 1) substrates has been carried out using X-ray diffraction (XRD) and transmission electron microscopy (TEM). All samples were deposited as a function of additive Ag content (x=0–6 at%), and annealed in the range of temperature, 300–600°C, for 1 h in order to obtain enhanced soft magnetic properties. Through XRD and TEM investigation, Ag-free Fe93Zr3B4 films on Si(0 0 1) substrates consisted of nano-crystalline Fe-based phases. In the presence of Ag additive element, the microstructure of as-deposited Fe93−xZr3B4Agx films consisted of a mixture of majority of Fe-based amorphous and Ag crystalline phases. In this case, additive element, Ag played a role in retarding the formation of Fe-based crystalline phases during deposition, and insoluble nano-crystalline Ag particles were dispersed in the Fe-based amorphous matrix. As the content of Ag increased, the intensity of Ag crystalline XRD peak increased. Crystallization of Fe-based amorphous phase in the matrix of Fe88Zr3B4Ag5 thin films occurred at an annealing temperature of 400°C. In the case of Fe88Zr3B4Ag5 films annealed at 500°C, a much enhanced permeability of the Fe-based alloy thin films associated with nano-crystalline phases was achieved.

In this study, strength and electrical conductivity of Cu-9Fe-1.2X (X = Ag or Cr) microcomposite wires obtained by cold drawing combined with intermediate heat treatments have been investigated. During cold working, the primary and secondary dendrite arms are aligned along the drawing direction and elongated into filaments. The addition of Ag was found to reduce the filament spacings at the given draw ratio throughout the drawing processing. The ultimate tensile strength and the conductivity of the Cu-Fe-Ag microcomposites were higher than those of Cu-Fe-Cr microcomposites, suggesting the refinement of the filaments is more effective than the strengthening of the filaments in strengthening the microcomposites. The strength of Cu-Fe-Xi microcomposites is dependent on the spacing of the Fe filaments in accord with a Hall-Petch relationship. The fracture surfaces of all the specimens showed ductile-type fracture and iron filaments occasionally observed on the fracture surfaces. The good mechanical and electrical properties in Cu-Fe-Ag wires may be associated with the more uniform distribution of the filaments than in Cu-Fe-Cr wires. The increase of the conductivity in Cu-Fe-Ag and Cu-Fe-Cr after intermediate heat treatments is attributed to the precipitation of Fe, Cr, or Ag particles, which dissolved during heavy deformation processing.

The microstructural and mechanical stability of Cu-6 wt. % Ag alloy obtained by cold rolling combined with intermediate heat treatments have been investigated. The stress-strain responses and fracture behavior of Cu-6 wt. % Ag alloy were examined and correlated with the microstructural change caused by thermo-mechanical treatments. The deformation bands stabilized by silver precipitates were observed in heavily rolled Cu-6 wt. % Ag alloy. The highly deformed microstructure stabilized by silver filament was observed to be unstable at temperatures above 200 °C. The strength of Cu-6wt.%Ag alloys were found to decrease remarkably if they were heat-treated above 300°C. The fracture surfaces of Cu-Ag two phase alloys showed typical ductile type fracture. The electrical conductivity did not change appreciably up to the aging temperature of 200°C and increased rapidly at temperatures above 300°C. The increase of the conductivity and the decrease of the strength can be associated with the microstructural coarsening of heavily deformed linear band structure. The difference of the UTS and the conductivity between the rolling direction and the direction perpendicular to the rolling direction (on the rolling plane) were found to be relatively small.

A laser diode which includes II–VI device structure directly grown on III–V device structure is proposed. This idea makes possible one-chip-multiple-wavelength operation in the visible wavelength region by the vertical integration of individual light emitters, which is demonstrated by a ZnCdSe/ZnSe/ZnMgBeSe quantum-well structure for a blue-green light emitter grown by molecular beam epitaxy directly on a metalorganic chemical vapor deposition grown InGaP/InGaAlP device wafer for a red light emitting device. The feasibility of the II–VI/III–V complex light emitter is demonstrated by optical-pumping experiments. Optically pumped lasing at 504 and 664 nm is achieved from II–VI and III–VI laser structures on one chip simultaneously at room temperature with a threshold power of 115 and 84 kW/cm2, respectively. The present results clearly show the feasibility of epitaxial integration of II–VI and III–V laser structures, which will stimulate the investigation of multifunctional optical devices.

Niobium doped TiO 2 thin films ((TiO 2 ) 1-x (Nb 2 O 5 ) x , x=0, 0.2 %, 0.4 %, 0.6 %, 0.8 %) were prepared on ITO-coated substrates by sol-gel method and spin coating technology followed by rapid thermal annealing treatment (RTA). The effects of various processing parameters, including Nb content (x=0–0.8 %) and annealing temperature, on the growth and properties of thin films were investigated. Structural characteristics by X-ray diffraction analysis indicated that the doping of Nb 2 O 5 in the TiO 2 without change the anatase structure of TiO 2 thin films. The absorption coefficient shows energy gap were decreased with increasing Nb 2 O 5 content from 3.29 eV for x=0 to 3.2 eV for x=0.8 %. Doping TiO 2 with Nb 2 O 5 can lower its band gap and shift its optical response to the visible region. It should be effective as a visible-light-driven photocatalyst.

N-type ZnTe layers with high electron concentration are grown by molecular-beam epitaxy using aluminum as the donor species. The ZnTe:Al layers show a high structural quality with a narrow x-ray diffraction linewidth (24 arcsec) and a high carrier concentration up to n=4×1018 cm−3 with low resistivity (ρ=0.017 Ω cm). The dependence of the electron mobility on the carrier concentration suggests that the dominant scattering mechanisms in the ZnTe:Al layers are ionized impurity scattering and polar optical phonon scattering. The photoluminescence spectrum of moderately doped ZnTe layers shows strong Al–donor-related bound exciton lines: I2 (2.378 eV) and donor–acceptor pair emission (zero phonon energy=2.324 eV) with a weak deep-level emission (2.19 eV). Highly Al-doped layers show an increase in the deep-level emission intensity and a decrease in carrier mobility, which are interpreted in terms of the increase in the carrier compensation.

A ZnCdTe/ZnTe/ZnMgSeTe quantum-well (QW) structure lattice matched to ZnTe is proposed for the light-emitting devices in the pure-green wavelength region. Thin ZnTe layers are inserted in between the ZnCdTe QW layer and ZnMgSeTe cladding layers, which improve the quality of the QW structure as demonstrated by its narrow photoluminescence line width (6.5 meV at 10 K). Optically pumped lasing at 552 nm at room temperature with a threshold optical power of 215 kW cm−2 is achieved. The present results clearly show the feasibility of ZnTe-based QW structures for the application to light-emitting devices in the pure-green wavelength region.

The OPERA neutrino oscillation experiment is based on the use of the Emulsion Cloud Chamber (ECC). In the OPERA ECC, nuclear emulsion films acting as very high precision tracking detectors are interleaved with lead plates providing a massive target for neutrino interactions. We report on studies related to the effects occurring from the contact between emulsion and lead. A low radioactivity lead is required in order to minimize the number of background tracks in emulsions and to achieve the required performance in the reconstruction of neutrino events. It was observed that adding other chemical elements to the lead, in order to improve the mechanical properties, may significantly increase the level of radioactivity on the emulsions. A detailed study was made in order to choose a lead alloy with good mechanical properties and an appropriate packing technique so as to have a low enough effective radioactivity., Comment: 19 pages, 11 figures

Ferroelectrics, which exhibit electric field dependent dielectric constant, have been of interest for possible applications on electrically controllable devices. Especially, dielectric constant of ferroelectrics could be adjusted in few microseconds to response on externally applied electric field, which made it possible ferroelectrics being used in microwave tunable devices. In this paper, Effect of BaSrTiO 2 /Li 2 CO 3 on low temperature sintering and BaSrTiO 2 /MgO on dielectric property of thick films has been investigated for variable capacitor on RF frequency band. The thick films were fabricated by the tape casting and then the structural and dielectric properties as a function of an addition composition of plastic-sizer ratio and sintering temperature were studied. For the thick film sintered at 1100°C, it was densified to 96 % of BaSrTiO 2 theoretical density by the addition of 3 and 10 w% BaSrTiO 2 /Li 2 CO 3 . Dielectric constant increased and tuning range increased with the increased of BaSrTiO 2 /Li 2 CO 3 content, which probably can be explained by the substitution of Ba 3+ , Li 1+ on BaTiO 3 lattice. The tunability and dielectric loss of the BaSrTiO 2 /Li 2 CO 3 thick film, sintered at 1150°C, were about 43 % and 0.234 at 10~15 MHz respectively. In case of BaSrTiO 2 /MgO, Dielectric constant decreased and tunability increased with the added of BaSrTiO 2 /MgO.

Conductivity control is one of the most important issues in wide band gap semiconductors such as ZnSe. Recently, we have reported the successful growth of high carrier concentration n-type ZnSe layers doped with Al. However, the carrier compensation mechanisms and limitation of carrier mobility has not been understood yet. In this work, a series of Al doped ZnSe samples were grown on semi-insulating [001] GaAs substrate by molecular beam epitaxy (MBE). High resolution X-ray diffraction (HRXRD) measurements were performed to investigate the doping induced structural changes. Optical properties of deep/near band emission were investigated by photoluminescence (PL). The electrical properties were investigated by Hall measurement at the elevating temperature.

We report on the influence of heat treatments on the electrical properties of ZnO films grown by molecular-beam epitaxy. We note that the electrical resistance of the ZnO films is significantly changed by the heat treatments: the electrical resistance increases with the increase of ambient temperature, but above a critical temperature the resistance decreases with the increase of temperature, irrespective of ambient gases. On the other hand, it is found that the large amount of photocurrent is generated in the ZnO films, exposed to white sources: the photocurrent decreases with the increase of the obtained resistance, and the current increases with the decrease of the resistance. Also, it is shown that the x-ray diffraction linewidth of the ZnO films is significantly decreased by the heat treatments. These indicate that the increase/decrease of the electrical resistance is ascribed to the annihilation/formation of the residual donor-type defects in the ZnO films by the heat treatments. It is suggested tha...

The authors report on an additional effect of the intentionally ordered GaInP layers obtained by using the double tilt GaAs substrates, i.e., the misoriented (001) GaAs substrates toward the two directions of [110] and [−110]. In photoluminescence (PL) spectra at 7 K, it is found that the emission intensity is enhanced with the increase in the substrate misorientation angle toward [−110] direction, along with the redshift of the bandedge. However, the redshift of the bandedge means that the GaInP layers suffer from the ordering of group III atoms. The authors note that the surface morphology in the ordered GaInP layers becomes rapidly rough by the substrate misorientation, even though the linewidths of their PL spectra and x-ray rocking curves are almost similar, irrespective of the misorientation angle. As a result, the light extraction mechanism in the roughened surface structure and the surface roughening mechanism in the intentionally ordered GaInP layers are suggested.

Fluorine-doped SnO2 (SnO2:F) films were prepared on Corning 7059 glass substrate in air atmosphere by pyrosol deposition method, starting with the solutions consisted of SnCl4 5H2O, NH4F, CH3OH, H2O and HCl. Textured SnO2:F films, obtained by optimizing the substrate temperature and the chemical compositions of solutions, had a specular transmittance of ~79%, a resistivity as low as ~4.3 × 10-4 ohm cm and a thickness of ~0.6μm. X-ray diffraction measurements showed that these films were polycrystalline with the tetragonal cassiterite structure and grew with a (200) preferred orientation. The room-temperature resistivity of films were fairly stable after heat-treatments up to 600°C in air.

We have extensively studied electrical properties for ZnO layers grown on GaN templates by molecular-beam epitaxy. First, the Schottky characteristics of Au contacts onto ZnO:N layers have been investigated by current-voltage measurements. Barrier heights and ideality factors for Au/ZnO:N Schottky contacts are systematically varied by controlling the growth temperatures and crystal-polar directions of ZnO:N layers. Second, the capacitance-voltage (C-V) characteristics of ZnO/GaN heterostructures has been investigated. Large plateau regions are observed in C-V characteristics, which are ascribed to the confined charges caused by band offset at the ZnO/GaN heterointerface. Finally, electron-trap centers in ZnO layers have been investigated by capacitance-temperature measurements. ZnO layers exhibit two electron-trap centers ET1 and ET2, whose thermal activation energies are estimated to be 33 and 0.15 eV, respectively.

The electrical characteristics of grain boundaries in polycrystalline silicon have been investigated. Experiments were performed using a focused laser beam to measure the GB parameters. Theoretical models of phonon-assisted and charge scattering processes are presented in relation to attenuation of the thermionic emission. The results indicate that the GB states behave as extrinsic impurity states which are not sensitive to the misorientation angle between grains. Both majority and minority carrier behavior are described.

Radiative and nonradiative trap centers for two typical sets of ZnSe:Al layers in a carrier compensation region, grown by molecular beam epitaxy, were investigated in terms of photoluminescence (PL) and photocapacitance (PHCAP) measurements. One set includes lightly doped ZnSe:Al layers whose net-doping density is 2×1018 cm−3, the other set includes heavily doped ZnSe:Al layers whose net-doping density is 1×1017 cm−3 due to carrier compensation. In 10 K PL spectra, the lightly doped ZnSe:Al layer shows dominant donor-bound exciton emission, while the heavily doped ZnSe:Al layer shows strong deep-level emission via radiative trap centers at 1.97 eV (RD1) and 2.23 eV (RD2). Moreover, the heavily doped ZnSe:Al layer shows another nonradiative electron trap center at 2.35 eV (ND3) in 100 K PHCAP spectra. Consequently, it is suggested the two radiative trap centers (RD1 and RD2) and one nonradiative trap center (ND3) contribute to carrier compensation in ZnSe:Al layers.

We have investigated the effect of a thin low-temperature-grown ZnSe (LT-ZnSe) buffer layer in improving ZnSe crystallinity by inserting it between the high-temperature-grown ZnSe epilayer and the GaAs substrate. In particular, the density of stacking fault defects, which is normally observed in ZnSe-based films grown on GaAs substrate, can be well reduced by inserting a thin LT-ZnSe buffer layer. A ZnSe film with stacking fault densities as low as ∼5.4×104/cm2 was obtained by growing on Zn exposed (2×4) As-stabilized surfaces of GaAs buffer layer with LT-ZnSe buffer, in contrast, ∼7×108/cm2 was obtained by directly growing on GaAs substrate, that is, without Zn exposure, LT-ZnSe, and GaAs buffer layers.

New methods for efficient and unambiguous interconnection between electronic counters and target units based on nuclear photographic emulsion films have been developed. The application to the OPERA experiment, that aims at detecting oscillations between mu neutrino and tau neutrino in the CNGS neutrino beam, is reported in this paper. In order to reduce background due to latent tracks collected before installation in the detector, on-site large-scale treatments of the emulsions ("refreshing") have been applied. Changeable Sheet (CSd) packages, each made of a doublet of emulsion films, have been designed, assembled and coupled to the OPERA target units ("ECC bricks"). A device has been built to print X-ray spots for accurate interconnection both within the CSd and between the CSd and the related ECC brick. Sample emulsion films have been extensively scanned with state-of-the-art automated optical microscopes. Efficient track-matching and powerful background rejection have been achieved in tests with electronically tagged penetrating muons. Further improvement of in-doublet film alignment was obtained by matching the pattern of low-energy electron tracks. The commissioning of the overall OPERA alignment procedure is in progress., Comment: 19 pages, 19 figures