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Light-emission contributed from discrete energy levels of self-assembly InGaN quantum dots is explored to fabricate broadband light-emitting diodes (LEDs). A series of InGaN quantum dots samples are self-assembly grown on sapphire substrate by metal-organic vapor phase epitaxy. Emission from the discrete energy states of the InGaN quantum dots is detected by micro-zone photoluminescence under cryogenic temperature. The peaks assignments are also verified by theoretical simulation. A green LED incorporating InGaN multi-quantum dots as active medium is fabricated, demonstrating a broader emission than the referred multi-quantum wells LED. It suggests quantum dots be of great potential to improve the color-rendering index of white LEDs.

We report AlGaN/GaN n-p-n heterojunction bipolar transistors (HBTs) on sapphire substrates with selective-area grown AlGaN emitters by metal–organic chemical vapor deposition. Metal–semiconductor contact on the external p-GaN base layer shows ohmic characteristics thanks to the dry-etching-free process of base–emitter junction. As a result, the maximum current gain $\beta $ is around 90 calculated from the Gummel plot of a ${20}\times {20}\,\,\mu \text{m}^{{2}}$ HBT device. Common-emitter ${I}$ – ${V}$ family curves exhibit offset voltage $({V} _{\text {offset}}) V and knee voltage $({V} _{\text {knee}}) V. A high current density $ {J}_{\text C}$ of 8 kA/cm2 and power density of 75 kW/cm2 were obtained. These values are the highest in the reported for GaN-based HBTs on sapphire substrates. The open-base breakdown voltage ( ${BV}_{\text {CEO}}$ ) exceeds 98 V comparable with direct-growth GaN-based HBTs.

This paper focus on studying how the instant centre impacts loads transfer in double wishbone suspension model when vehicle moving straight (brakes or accelerates), instant center could further affects loads transfer by affecting inverse geometry values, worldwide specialists defined different ways to prove that instant centre has massive influences on the anti-geometry values. This paper by creating the double wishbone suspension Adams model and relatively auxiliary model to verify those theories and compare the results to find out the most accurate way to calculate anti-geometry value. Furthermore, this paper also proves the change of anti-geometry will affect tyre vertical and longitudinal loads transfer to resist the dive and squat of vehicle body when car brakes or accelerates.

Photodetectors for the ultraviolet (UV) range of the electromagnetic spectrum are in great demand for several technologies, but require the development of novel device structures and materials. Here we report on the high detectivity of UV photodetectors based on well-ordered laterally mesoporous GaN. The specific detectivity of our devices under UV-illumination reaches values of up to 5.3 × 1014 Jones. We attribute this high specific detectivity to the properties of the mesoporous GaN/metal contact interface: the trapping of photo-generated holes at the interface lowers the Schottky barrier height thus causing a large internal gain. High detectivity along with a simple fabrication process endows these laterally mesoporous GaN photodetectors with great potential for applications that require selective detection of weak optical signals in the UV range.

A high-resistance buffer layer is critical for GaN-based high electron mobility transistors (HEMTs) to suppress the drain leakage current and pre-mature device breakdown. A typical method to obtain the HR buffer layers is the acceptor impurity doping that is able to provide holes to compensate the background electrons in the buffer layers. However, the intentional doped acceptor impurities such as Mg, Fe and C will result in current collapse in GaN-based HEMTs. To address this issue, in this work, we employed a polarization doping method of holes by Al-composition grading instead of the acceptor impurity doping. The sheet resistance of the GaN-based buffer layer significantly increased due to the holes generated by the polarization field. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

In this study, gallium nitride (GaN) films were grown on the quartz glass substrates using metal organic chemical vapor deposition with AlN buffer layer. The AlN layer was deposited using rf-magnetron sputtering. Although the direct nucleation of GaN on quartz glass substrate is difficult, with AlN as the nucleation layer, a large-area polycrystalline GaN film can be obtained. The structural and optical properties were investigated. The results show that the GaN film has a preferential orientation along (0002). There are mainly three emission regions in the photoluminescence spectra, including the band-edge, green (2.45-2.55eV) and yellow (2.0-2.35 eV) emission regions. The origin and temperature dependence of the peak position, full-width of half-magnitude and intensity were also discussed. The findings may help to understand the growth and improve the properties of GaN film grown on amorphous glass substrates. (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

GaN-based ridge waveguides with very smooth and vertical sidewalls are fabricated by combined inductively coupled plasma (ICP) etching and wet chemical etching. The height of GaN waveguide is precisely controlled by ICP dry etching, while smooth and vertical sidewalls are realized by wet chemical etching. Compared with waveguides with rough sidewalls just after ICP etching, the propagation loss of waveguides with wet-etched smooth sidewalls was reduced by about 2 dB mm−1 at 1.55 µm. Propagation loss can be further reduced by improving the quality of GaN epitaxial layers.

We reported the combination of micro-pyramid active layers and graphene electrode to realize the phosphor-free InGaN based white light emitting diodes (LEDs). SEM and TEM measurements were used to characterize the structural qualities of the micro pyramid arrays. According to CL and EDX analyses, the two emitting peaks originated from the indium segregation during the MOCVD process. Multilayer graphene was used to simplify the fabrication process for the electrical connection of the micro-pyramid arrays. The wavelength shift of two emitting peaks were both small with the increase of injection currents, indicating the weak QCSE. What was more, the reverse current leakage was also quite low for the phosphor-free InGaN micro-pyramid white light emitting diodes arrays connected by graphene.

In this work, the effects of growth pressure and growth rate on electrical and structural properties of Mg-doped GaN were investigated. It has been shown that enhanced growth rates induced by higher growth pressures may lead to decreased structural and electrical properties of p-type GaN layers. If the growth rate is kept unchanged, higher growth pressures will be beneficial for the quality of Mg-doped GaN due to the enhanced NH3 overpressure.

A study about the achievement of dichromatic white light-emitting diodes (LEDs) was performed. A series of dual wavelength LEDs with different last quantum-well (LQW) structure were fabricated. The bottom seven blue light QWs (close to n-GaN layer) of the four samples were the same. The LQW of sample A was 3 nm, and that of sample B, C and D were 6 nm, a special high In content ultra-thin layer was inserted in the middle of the LQW of sample C and on top of that of sample D. XRD results showed In concentration fluctuation and good interface quality of the four samples. PL measurements showed dual wavelength emitting, the blue light peak position of the four samples were almost the same, sample A with a narrower LQW showed an emission wavelength much shorter than that of sample B, C, D. EL measurement was done at an injection current of 100 mA. Sample A only showed LQW emission due to holes distribution. Because of wider LQW, the emission wavelength of sample B, C and D was longer and peak intensity was weaker. Sample D with insert layer on top of LQW showed strongest yellow light emission with a blue peak. As the injection current increased, sample A showed highest output light power due to narrower LQW. Of the other three samples with wider LQW, sample D showed highest output power. Effective yellow light emission has always been an obstacle to the achievement of dichromatic white LED. Sample D with insert layer close to p-GaN can confine the hole distribution more effectively hence the recombination of holes and electrons was enhanced, the yellow light emission was improved and dichromatic white LED was achieved.

A study on the effect of Mg doping in quantum-well (QW) layers on dual-wavelength light-emitting diodes (LEDs) was performed. A series of dual-wavelength LEDs with different Mg doping conditions were fabricated. According to electroluminescence measurement, as the Mg doping concentration and regions varied, improved hole distribution and bottom-QW emission was achieved. This result is in accord with APSYS simulation. In addition, the sample with Mg doping in all QWs showed the highest output power and smallest efficiency droop. It is concluded that Mg doping in QWs could ameliorate the optical and electrical properties of dual-wavelength LEDs.

A study about the effect of Mg doping in specified quantum-barrier on dual wavelength light emitting diodes (LEDs) was performed. A series of dual wavelength LEDs with different Mg doping conditions and barrier thickness were fabricated. According to electroluminescence measurement, as Mg doping concentration and barrier thickness varied, improved carrier distribution and bottom QWs emitting was achieved. This result is in accord with APSYS simulation. In addition, the sample with appropriate Mg doping level showed dual wavelength emitting. It is concluded that Mg doping in specified quantum-barrier could improve optical and electrical properties of dual wavelength LEDs.

Since the terrain slope cannot be neglected for forest height inversion with polarimetric synthetic aperture radar interferometry (PolInSAR), a sloped random volume over ground (S-RVoG) model is proposed to correct the terrain distortion for forest parameters estimation. A significant model complexity reduction is achieved by aligning the reference frame along the local terrain slope and changing the corresponding radar geometrical configuration. The proposed S-RVoG model inversion promises to provide much more accurate estimation of forest parameters and is validated with L-band PolInSAR data produced by PolSARpro software developed by the European Space Agency (ESA).

Bulk perovskite manganese oxide La1−xSbxMnO3 (x=0.05,0.1) samples were prepared using solid-state reaction technology. Electrical transport and magnetic properties have been investigated. The experimental results show that the compound exhibits typical colossal magnetoresistance (CMR) behavior. The temperature and time dependence of magnetization [M(T) and M(t)] confirm that the compounds are in cluster glass state at temperatures lower than Curie temperature. The zero-field-cooled magnetization strongly depends on the observed time, and all M(t) curves have an inflection point at an observation time very close to wait time tw. All our results show that the La1−xSbxMnO3 (x=0.05, 0.1) compound is a CMR oxide with a MR ratio of about 60% at 225 K and 5 T. X-ray photoelectron spectroscopy analysis has revealed that the Sb cation is in quin-valence state and the new compound could be considered as an electron doped system.

We have used transmission electron microscopy and characterized the microstructure in thin films of La1-xTexMnO3 (x = 0.1, 0.2) compounds, which are new additions to the family of colossal magnetoresistance (CMR) oxides. Electron diffraction and high-resolution imaging reveal that Te-doped thin films with a thickness of 100 nm for x = 0.1 and 200 nm for x = 0.2 are epitaxially grown on the SrTiO3 (001) substrate. On the basis of electron diffraction patterns obtained from cross-section and plan-view specimens, the new compounds are determined to have an orthorhombic unit cell with lattice parameters a(o) approximate to 2(1/2) a(p) = 0.54 nm, b(o) approximate to 2a(p) = 0.77 nm, c(o) approximate to 2(1/2) a(p) = 0.54 nm, where a(p) is the lattice parameter of an ideal cubic perovskite structure, 0.39 nm. The microstructures in orthorhombic La1-xTexMnO3 compounds are clarified in terms of two 90degrees-oriented domains, both of which are grown with [101] axis perpendicular to the substrate surface. (C) 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

A surface plasmon (SP)-enhanced nanoporous GaN-based green LED based on top-down processing technology has been successfully fabricated. This SP-enhanced LED consists of nanopores passing through the multiple quantum wells (MQWs) region, with Ag nanorod array filled in the nanopores for SP-MQWs coupling and thin Al(2)O(3) passivation layer for electrical protection. Compared with nanoporous LED without Ag nanorods, the electroluminescence (EL) peak intensity for the SP-enhanced LED was greatly enhanced by 380% and 220% at an injection current density of 1 and 20A/cm(2), respectively. Our results show that the increased EL intensity is mainly attributed to the improved internal quantum efficiency of LED due to the SP coupling between Ag nanorods and MQWs.

GaN-based ridge waveguides with very smooth and vertical sidewalls are fabricated with combined inductively coupled plasma (ICP) etching and chemical etching. Reduction in scattering loss is estimated to be 2 dB/mm at 1.55 μm.

The adsorption of water molecules in active carbon in normal condition can be monitored in situ with an oblique-incidence polarization-modulated optical reflectance difference technique. The optical response cannot only characterize the time length of adsorption, but reveal the tendency of dielectric properties of active carbon during the adsorption process. Therefore, the whole adsorption can be described by the permittivity obtained by OIRD measurement. Such a technique is also effective under high ambient pressure and temperature because of the optical detection, indicating that the precise measurement carried with this technique can help in building adsorption theory system in some different conditions.

Polarization-reversed electron-blocking structure, which had negative polarization charges localized at the interface between the last quantum barrier (LQB) and electron-blocking layer (EBL), was demonstrated to remarkably improve the light-emitting efficiency of GaN-based blue light-emitting diodes (LEDs) numerically and experimentally. The improvement was attributed to the enhanced electron-blocking effectiveness by the elevated conduction band nearby the LQB/EBL interface. Nevertheless, the efficiency droop was not mitigated because the decrease of electron-leakage was accompanied by the increase of Auger recombination.

Based on the requirements for studying the dynamic process of proteinase action substrates in life science, we selected six random proteins including 1L-10, SCGB2A2, CENPQ, GST, HK1, KLHL7, as well as five different concentrations of 1L-10 proteins of 1 mg/ml, 0.5 mg/ml, 0.25 mg/ml, 0.125 mg/ml, and 0.0625 mg/ml, and fabricated two types of substrate protein microarrays, respectively. We detected the dynamic processes of proteins degraded by proteinase K using oblique-incidence reflectivity difference (OIRD) method in a label-free and real-time manner. We obtained the relevant degradation velocities and the degradation time. The experimental results demonstrate that OIRD has the ability to study proteinase action substrates which is out of reach of label methods and is expected to offer opportunities to determine protease-substrate relationships on the systems biology level.

The structural relaxation and crystallization processes of the Cu50Zr50 amorphous alloy have been studied by field ion microscopy (FIM) on an atomic scale. An interesting phenomenon which we call the clustering effect was observed for the first time as far as we know. In the temperature range 673–723 K, clusters consisting of 3, 4, or 5 atoms formed and migrated towards certain crystalline centers. They then combined with one another and rearranged to produce an ordered atomic array. This clustering process including the formation, migration, combination and rearrangement of clusters is considered as a structural relaxation process.

Investigations of crystallization on the Cu30Zr70 amorphous alloy surface are carried out by differential scanning calorimetry (DSC) and X-ray photoelectron spectroscopy (XPS). The results show that the crystallization behavior on the surface of the sample is different from that in the bulk. The crystallization process may start from the surface and then propagate into the bulk. It is due mainly to the diffusion and segregation of Zr in the Cu30Zr70 sample toward the surface induced by oxygen and lattice strain during the annealing treatment. The oxide of Zr is observed on the surface, and by decomposition of the Zr3d spectra of the Cu30Zr70 sample, the presence of sub-oxide ZrO is established, their binding energy (3d5/2 peak) locates near 181 eV. It is formed due to the oxygen existing in the sample environment, the element Zr oxidizes and becomes strongly enriched on the surface.

The interfacial oxygen diffusion during film growth often results in the appearance of a thin ${\mathrm{SiO}}_{x}$ layer in ${\mathrm{SrTiO}}_{3}∕\mathrm{Si}$ films and related heterojunctions. High-resolution TEM investigations on the ${\mathrm{La}}_{0.9}{\mathrm{Sr}}_{0.1}{\mathrm{MnO}}_{3}∕{\mathrm{SrTiO}}_{3}∕\mathrm{Si}(\mathrm{LSMO}∕\mathrm{STO}∕\mathrm{Si})$ heterojunctions suggested that the thickness and microstructure of the ${\mathrm{SiO}}_{x}$ interfacial layer change visibly from one sample to another grown under slightly different conditions. Electron diffraction observations demonstrated the epitaxial relationships in the $\mathrm{LSMO}∕\mathrm{STO}∕\mathrm{Si}$ heterojunction as ${[001]}_{\mathrm{LSMO}}\ensuremath{\Vert}{[\ensuremath{-}110]}_{\mathrm{Si}}$, ${[110]}_{\mathrm{LSMO}}\ensuremath{\Vert}{[001]}_{\mathrm{Si}}$ and ${[001]}_{\mathrm{STO}}\ensuremath{\Vert}{[001]}_{\mathrm{Si}}$, ${[010]}_{\mathrm{STO}}\ensuremath{\Vert}{[\ensuremath{-}110]}_{\mathrm{Si}}$. The electron energy loss spectroscopy analyses on the $\mathrm{LSMO}∕\mathrm{STO}∕\mathrm{Si}$ interfacial region indicated that the Si ions are in intermediate oxidation states in the amorphous layer and the interfacial Ti bonding changes slightly. Electron holography measurements indicated that the energy barrier between the Si substrate and the LSMO film is about $0.95\ifmmode\pm\else\textpm\fi{}0.16\phantom{\rule{0.3em}{0ex}}\mathrm{V}$, where notable negative charges accumulate in the amorphous ${\mathrm{SiO}}_{x}$ layer.

A compact 120 TW/36 fs Ti:sapphire chirped pulse amplification laser was established. Using the pumping pulse with accurate synchronization in final amplifier, 5.98 J/220 ps output was achieved for /spl sim/300 mJ incident pulse, the single amplifier gain reaches /spl sim/20.

We report the observation of hundreds of oscillations in oblique-incidence optical reflectivity difference from a growth surface of Nb-doped ${\text{SrTiO}}_{3}(100)$ during a continuous, pulsed-laser deposition. Similar to in-phase specular reflection of thermal helium atoms or electrons, the optical oscillations originate from an oscillatory change in step density on the surface and the different optical dielectric response of step edge atoms (or unit cells) from those in the flat terraces.

In this paper, we report the magnetic and electrical properties of the Te-doped lanthanum manganite perovskite compound La 1 - x Te x MnO 3 and the related electron spin resonance (ESR) study. This is a material with rhombohedral structure and it shows good colossal magnetoresistance behavior. The magnetoresistance ratio MR=[ρ(0)-ρ(H)]/ρ(0)is about 63% for x=0.04 in an applied magnetic field of 40 kOe. The resistivity of the compounds is affected by temperature and the amount of Te doping. The temperature dependence of the resistivity showed that the conductivity above the Curie temperature was dominated by the hopping of the small polarons, and the resistance was attributed to the electron-phonon and magnon scattering mechanism below the metal-insulator transition temperature. The ESR investigation indicated that the compound was in the paramagnetic phase above 230 K, and in the single ferromagnetic state below 170 K. In the temperature range of 230 to 170 K, the compound showed phase separation phenomena.

We reported that the peak efficiency together with the efficiency droop in InGaN-based light emitting diodes could be effectively modified through a simple and low-cost etch-regrown process in n-GaN layer. The etched n-GaN template contained pyramid arrays with inclined side planes. The following lateral overgrowth process from the etched n-GaN template substantially reduced the edge dislocation density and residential compressive strain in epilayers. The efficiency droop of LED samples thus could be modified due to the reduced polarization field, resulting from the strain relaxation in epilayers. What is more, the peak efficiency and reverse current leakage were also modified due to the reduction of dislocations.

A novel nanopattern technique of nanospherical-lens photolithography is introduced to fabricate the InGaN nanopyramid white (NPW) light-emitting diodes (LEDs) by selective area growth. Highly ordered NPW LED arrays are achieved after optimizing the growth conditions. It is found that the NPW LEDs vary from warm white light to cool with the increase in growth temperature. For the cool white NPW LEDs, the spectrum is similar to the conventional white LEDs obtained from the blue LEDs combined with yellow phosphors. The blue emission originates from the upper sidewalls of nanopyramids, and yellow light is mainly emitted from the lower ridges with respect to the base of nanopyramids. Furthermore, simulation shows that the light extraction efficiency of NPW LEDs is about 4 times higher compared with conventional ones, and the escape cone is as much as 85° due to their three-dimensional nanopyramid structures. These observations suggest that the proposed phosphor-free NPW LEDs may have great potential for highly efficient white lighting.

Self-assembly SiO2 nanosphere monolayer template is utilized to fabricate nanopatterned sapphire substrates (NPSSs) with 0-nm, 50-nm, and 120-nm spacing, receptively. The GaN growth on top of NPSS with 0-nm spacing has the best crystal quality because of laterally epitaxial overgrowth. However, GaN growth from pattern top is more difficult to get smooth surface than from pattern bottom. The rougher surface may result in a higher work voltage. The stimulation results of finite-difference time-domain (FDTD) display that too large or too small spacing lead to the reduced light extracted efficiency (LEE) of LEDs. Under a driving current 350 mA, the external quantum efficiencies (EQE) of GaN-based LEDs grown on NPSSs with 0-nm, 50-nm, and 120-nm spacing increase by 43.3%, 50.6%, and 39.1%, respectively, compared to that on flat sapphire substrate (FSS). The optimized pattern spacing is 50 nm for the NPSS with 600-nm pattern period.

We reported a high-efficiency and low-cost nano-pattern method, the nanospherical-lens photolithography technique, to fabricate a SiO2 mask for selective area growth. By controlling the selective growth, we got a highly ordered hexagonal nanopyramid light emitting diodes with InGaN/GaN quantum wells grown on nanofacets, demonstrating an electrically driven phosphor-free white light emission. We found that both the quantum well width and indium incorporation increased linearly along the {10 (1) over bar1} planes towards the substrate and the perpendicular direction to the {10 (1) over bar1} planes as well. Such spatial distribution was responsible for the broadband emission. Moreover, using cathodoluminescence techniques, it was found that the blue emission originated from nanopyramid top, resembling the quantum dots, green emission from the InGaN quantum wells layer at the middle of sidewalls, and yellow emission mainly from the bottom of nanopyramid ridges, similar to the quantum wires.

The InGaN multiple quantum well light-emitting diodes (LEDs) with different sizes of indium-tin-oxide (ITO) nanobowl photonic crystal (PhC) structure has been fabricated using self-assembled monolayer nanosphere lithography. The light output power (LOP) of PhC LEDs (at 350 mA) has been enhanced by 63.5% and the emission divergence exhibits a 28.8° reduction compared to conventional LEDs without PhC structure. Current-Voltage curves have shown that these PhC structures on ITO layer will not degrade the LED electrical properties. The finite-difference time-domain simulation (FDTD) has also been performed for light extraction and emission characteristics, which is consistent with the experimental results.

Self-assembled InGaN quantum dots (QDs) were fabricated by metal-organic chemical vapor deposition. Abnormal temperature dependence of photoluminescence (PL) was observed. The integrated PL intensity of QDs sample shows a dramatic increase in a temperature range from 160 K to 215 K and reaches the maximum value at 215 K instead of 10 K as usual. To interpret this phenomenon, a theoretic model of temperature induced carrier redistribution mechanism is designed using rate equation, which fits closely with the experimental result. It is concluded that carriers’ redistribution from shallow QDs or wetting layer to deep QDs gives rise to the unique behavior for InGaN QDs structure.

With the oblique-incidence reflectivity difference (OIRD) technique, we successfully label-free detected the interaction of swine IgG with different concentrations of 0.125, 0.25, 0.5, 1 mg/ml, and 5 μg/ml goat anti-swine IgG, and real-time detected the reaction dynamic processes of 0.5 mg/ml swine IgG and goat anti-swine IgG with different concentration of 5, 10, and 20 μg/ml, respectively. The interaction times are about 2043, 1828, and 1347 s for the reactions of 0.5 mg/ml swine IgG and goat anti-swine IgG of 5, 10, and 20 μg/ml, respectively. By fitting the reaction dynamic curves, we obtained that the association constant of swine IgG and goat anti-swine IgG is 1620.77 M−1·S−1 at temperature about 22 °C. The experimental results demonstrate that the OIRD is a promising and competing method for label-free and real time detecting the biomolecular interactions and achieving the quantitative information of reaction kinetics.

We report on the effect of a graded AlGaN electron blocking layer (GEBL) on the emission properties of InGaN/GaN multiple quantum wells light-emitting diode (LED). The adoption of GEBL in the LED enhances the electroluminescence intensity and reduces the wavelength blue-shift with increasing injection current. The light output power of the GEBL LED is enhanced by 163% and 415% at 20 and 350 mA, respectively. Moreover, the forward voltage of the GEBL LED is reduced by 0.38 V at the forward current of 20 mA.

In this study, the angular distributions of harmonics emission from aligned CO2 are explored experimentally and theoretically, and the validity of Strong Field Approximation (SFA) model in the molecular high harmonic generation is therefore studied. The study shows that for describing the angle distribution of high harmonic generation from molecules, SFA is roughly consistent with the qualitative analysis, while the quantitative analysis is different.

The annealing of Mg-doped GaN with Pt and Mo layers has been found to effectively improve the hole concentration of such material by more than 2 times as high as those in the same material without metal. Compared with the Ni and Mo catalysts, Pt showed good activation effect for hydrogen desorption and ohmic contact to the Ni/Au electrode. Despite the weak hydrogen desorption, Mo did not diffuse into the GaN epilayer in the annealing process, thus suppressing the carrier compensation phenomenon with respect to Ni and Pt depositions, which resulted in the high activation of Mg acceptors. For the GaN activated with the Ni, Pt, and Mo layers, the blue emission became dominant, followed by a clear peak redshift and the degradation of photoluminescence signal when compared with that of GaN without metal.

InGaN/GAN multiple quantum wells grown by metal-organic chemical vapor deposition were irradiated with the electron beam from a low energy accelerator. The electron irradiation induced a redshift by 50 meV in the photoluminescence spectra of the electron-irradiated InGaN/GaN quantum wells, irrespective of the exposure time to the electron beam which ranges from 10 to 1000s. The localization parameter extracted from the temperature-dependent photoluminescence spectra was found to increase in the Irradiated samples. Analysis of the intensity of the longitudinal optical phonon sidebands showed the enhancement of the exciton-phonon coupling, indicating that the excitons are more strongly localized in the irradiated InGaN wells. The change in the pholotuminescence spectra. In the irradiated InGa/GAN quantum wells were explained in terms of the increase of indium concentration in indium rich clusters induced by the electron irradiation (C) 2009 The Japan Society of Applied Physics

Polycrystalline BiMn2O5 and Bi0.9Ce0.1Mn2O5 have been prepared by a solid-state reaction. A crystalline structure study shows that all x-ray diffraction patterns can be indexed successfully in an orthorhombic phase. Substitution of Ce for Bi ions induced in the unit cell a slight distortion and enlargement. Magnetic and dielectric measurements all reveal that Ce substitution induces great effects: BiMn2O5 is in the antiferromagnetic (AFM) phase with a Neel transition temperature at about 42K, whereas Bi0.9Ce0.1Mn2O5 is in the ferromagnetic (FM) phase with a Curie temperature at about 46K. The permittivity of Bi0.9Ce0.1Mn2O5 is much higher than that of BiMn2O5, and two dielectric relaxation peaks have been observed in the former, instead of one dielectric loss peak as observed in BiMn2O5. The valent state of Ce ions has been analyzed mainly as tetravalent by the core-level spectrum of Ce 3d from x-ray photoemission spectroscopy. The possible mechanisms of the magnetic transition from AFM to FM and the pecu...

Si–Ba0.5Sr0.5TiO3 composite thin films were deposited by pulsed laser deposition technique on (100) Nb:SrTiO3 substrates. The crystal structure and surface morphology of the thin films have been characterized by x-ray diffraction and atomic force microscopy, respectively. Experimental results suggested that the Si composition has played a positive role in improving the dielectric properties of the thin films. With the increased Si concentration, the dielectric loss was significantly reduced, accompanied with a tolerable reduction of tunability. In particular, the 14% Si composite film exhibited a dielectric loss of 0.005, which is much lower than that of the undoped Ba0.5Sr0.5TiO3 (BST) film. Moreover, a proper concentration of Si in the film improved the figure of merit from 9 of the undoped BST to 23 of 1.4% Si composite films.

Large positive magnetoresistance (MR) and high MR sensitivity in low magnetic fields have been discovered in the Sr-doped LaMnO3 and Nb-doped SrTiO3 p-n junctions fabricated by laser molecular-beam epitaxy. The MR ratios, defined as DeltaR/R-0, DeltaR = R-H-R-0, are observed as large as 11 % in 5 Oe, 23 % in 100 Oe, and 26 % in 1000 Oe at 290 K; 53% in 5 Oe, 80 % in 100 Oe, and 94 % in 1000 Oe at 255 K. The MR sensitivities are 85 Omega/Oe at 290 K, 246 Omega/Oe at 255 K, and 136 Omega/Oe at 190 K, respectively, with the applied magnetic field changed from 0 to 5 Oe. The positive MR ratios and high MR sensitivities of the p-n junctions are very different from that of the LaMnO3 compound family. (C) 2005 American Institute of Physics.