Photoresponse of the In0.3Ga0.7N metal-insulator-semiconductor photodetectors

In0.3Ga0.7N metal-insulator-semiconductor （MIS） and metal-semiconductor （MS） surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition （MOCVD）. The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.     

Enhancement in multiferroic properties of Bi0.7−xLaxDy0.3FeO3 system with removal of La

La doping at Bi Site in multiferroic BiFeO₃ (BFO) is known to stabilize the ferroelectric perovskite phase and reduce the leakage current. It has been observed that in Dy modified BFO sample, La is not required for the said reason. In fact, the removal of La from Dy modified BFO system leads to the reduction in leakage current. Moreover, the magnetic properties are enhanced by order of magnitude in the absence of La in the system. Remarkably, a similar trend in properties has been also observed in thin films grown on Pt/TiO₂/SiO₂/Si substrate by using the pulsed laser deposition technique. This significant variation in the properties after removal of La from the system could be attributed to the change in lattice parameters, bond lengths and Fe–O–Fe bond angle as determined by powder x-ray and neutron diffraction study.     

Investigation of ultra wideband multi-channel dichroic beamsplitters from 0.3 TO 52 μm

The developmer of a set of multi-channel dichroics which includes a 6 channel dichroic operating over the wavelength region from 0.3 to 52 μm is described. In order to achieve the optimum performance, the optical constants of PbTe, Ge, and CdTe coatings in the strongly absorptive region have been determined by use of a new iterative method using normal incidence reflectance measurement of the multilayer together with initial values of energy gap Eg and infinite refractive index n∞ for the semiconductor model. The design and manufacture of the dichroics is discussed and the final results are presented.     

Dielectric and piezoelectric properties of (1−x)Ba0.7Sr0.3TiO3−xBa0.7Ca0.3TiO3 perovskites

Dielectric and piezoelectric properties of (1?x)Ba_0.7Sr_0.3TiO₃?xBa_0.7Ca_0.3TiO₃ (BST?xBCT) (x=0.2–0.9) perovskite ceramics have been investigated. BCT has fully incorporated into BST lattice, forming a complete perovskite solid solution, whose lattice constant χ decreases almost linearly with increase in x from 0.2 to 0.4, while showing an anomalous expansion at 0.4<x≤0.6. This, together with the deviation of tetragonal–orthorhombic phase transition temperature (T_O–T) from the linear relation T_O–T (K)=?103.7x+239.3 at x=0.5, suggests that a small amount of Ca²⁺ has substituted for Ti⁴⁺. Curie temperature T_C increases linearly with increase in x from 0.2 to 0.9, which is mainly contributed to the increase of the Ba/Sr ratio. The calculated degree of relaxation (γ) is in the range of 1.41–1.53, indicating that the BST–xBCT ceramics are ferroelectric materials with diffuse phase transition. Strain and piezoelectric constant (d₃₃) decrease with increasing x, whereas planar electromechanical coefficient (k_p) reaches a maximum (17.0%) at x=0.6.     

Structural and Mössbauer spectroscopic studies of Fe0.7−xCrxAl0.3 alloys

Fe_0.7−xCr_xAl_0.3 alloys with x=0, 0.1, 0.2, 0.3 and 0.35 have been synthesized by arc melting and studied by X-ray diffraction and Mössbauer spectroscopy. All the samples studied were found to have single phase with body center cubic structure. The lattice parameter a, and hence the volume, were obtained from the X-ray diffraction patern and found to increase with increasing the chromium concentration. At room temperature Mössbauer studies show magnetic ordering for small values of x and paramagnetic behavior for large values of x under investigation. The Mössbauer spectra were analyzed considering a distribution of magnetic hyperfine fields for small values of x and two singlets were added for large values of x. During the fitting procedure, the relation between the hyperfine field and the isomer shift in the hyperfine field distribution was linear relation. The average hyperfine field and isomer shift as a function of chromium content x were found to decrease with increasing x. The results are explained in terms of local environmental effects on the hyperfine interactions.     

Ultrafast Photoelectric Effects in Heterojunctions of La0.7Sr0.3MnO3 and Si

Ultrafast photoelectric effects have been observed in p-n heterojunctions of La0.7Sr0.3MnO3(LSMO)/Si and LSMO/SrTiO3_/Si for the first time. The rise time was about 1 ns and the full width at half maximum was about 2ns for the photovoltaic pulse when the heterojunction was irradiated by a laser of -25 ps pulse duration and 1064 nm wavelength. The photovoltaic sensitivity was as large as 435 mV//mJ for a 1064 nm laser pulse. No such pulse was observed with irradiation from a pulsed 10.6 μm CO2 laser.     

Theoretical Study of Compressibility and Thermoelasticity of LaNi5-xAlx （x= 0.3, 0.5 and 1.0）

The compressibility, the temperature dependence of bulk modulus, the pressure dependence of normalized volume V/V0, thermal expansion coefficient and Debye temperature of LaNi5-xAlx compounds are successfully obtained using the first-principles plane-wave pseudopotential （PW-PP） method, the EOSFIT6.0 software and the quasiharmonic Debye model. The rapid decrease of relative lattice constant a/a0 shows that the deformation is easier in directions normal to the c-axis than that along it. The relationships between bulk modulus B and pressure at different temperatures are also analysed. It is found that the bulk modulus B increases monotonically with increasing pressure. Moreover, the pressure dependences of thermal expansion and Debye temperature are also successfully obtained. The calculated results are in agreement with the experimental data.     

Thermal conductivity of the “light” heavy-fermion compound YbIn0.7Ag0.3Cu4

This paper reports on the electrical resistivity and thermal conductivity of polycrystalline YbIn_0.7Ag_0.3Cu₄ at temperatures from 4.2 to 300 K, which exhibits, at T _v , a continuous isostructural first-order phase transition from a Curie-Weiss paramagnet with localized magnetic moments (for T>T _v ) to a Pauli paramagnet in a nonmagnetic Fermi liquid state with the Yb ion in a mixed valence state (for T<T _v ). It is shown that for T<T _v , the Lorenz number behaves in accordance with the theoretical model developed for heavy-fermion materials, while for T>T _v , it acquires the value typical of standard metals.     

The Second Threshold Field of Charge-Density-Wave Conductor Rb0.3MoO3 in High Temperature Range

The switching and threshold properties of quasi-one-dimensional charge-density-wave conductor rubidium blue bronze Rb0.3MoO3 single crystals are investigated in a comparative high and large temperature range. Beyond the limit temperature 50K of Littlewood‘s theory, even up to about lOOK, typical sharp switching to negative or zero differential resistance is observed in E-I characteristic curves. Correspondingly, an obvious switching between two conducting states, from a lowly conducting state to a highly conducting state, is observed in the I-E characteristic curves in the same temperature range. Temperature dependence of the second threshold field ET2 accompanied by this kind of high field switching behaviour is firstly obtained. These new observations are discussed in the mechanism of the current inhomogeneity and redistribution due to the existence of transverse energy barriers suggested by Zhang et al. [Solid State Commun. 85 (1993) 121]     

Influence of processing conditions on the crystal structure and magnetic behavior of La0.7Ca0.3MnO3±δ samples

In this work we report crystallographic structure variations and the related modifications on the magnetic behavior of La_0.7Ca_0.3MnO_3±δ introduced by heat-treatments in different synthesis atmospheric conditions. We have prepared polycrystalline ceramic samples using a modified polymeric precursors method, which produces highly homogeneous specimens.The use of argon atmosphere enlarges the crystalline c-axis as detected by Rietveld refinements. As a consequence, an improvement in the magnetic transition temperature T_C of the samples was observed.Our results also indicate that different heat-treatment conditions change the magnetic interactions between the ferromagnetic (F) and antiferromagnetic (AF) structures of these systems. Our conclusions rely on the use of AC magnetic susceptibility measurements as the experimental tool for measuring these variations.     

Negative thermal expansion property of Er0.7Sr0.3NiO3 − δ

A new kind of negative thermal expansion (NTE) material of Er_0.7Sr_0.3NiO_3 − δ is synthesized by solid-state method and investigated. It is found that Er_0.7Sr_0.3NiO_3 − δ crystallizes in orthorhombic structure with rod-shaped grains. Ceramic Er_0.7Sr_0.3NiO_3 − δ exhibits NTE coefficient of $-39.0\times {10}^{-6}{\text{K}}^{-1}$ from 655 to 780 K. The results of X-ray diffraction, temperature dependence of Raman spectroscopy and differential scanning calorimetry (DSC) suggest that the NTE phenomenon relates to its phase transition from orthorhombic to rhombohedral.     

Study on the Lorentz detuning and tuning of β=0.3, 352 MHz spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β=0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.     

Electroresistance and field effects in epitaxial thin films of Pr0.7Sr0.3MnO3

Highly epitaxial thin films of Pr_0.7Sr_0.3MnO₃ were grown on (100) SrTiO₃ single crystal substrates by laser ablation. Similar to other manganite compounds, these Pr_0.7Sr_0.3MnO₃ films exhibited remarkable magnetoresistance. Application of electric currents could induce a remarkable reduction in resistivity, demonstrating a strong electroresistance effect. The ratio of the resistance variation, ER=[R(0)−R(I)]/R(I), is about 33% at metal-insulator transition temperature. Using a planar field effect configuration, significant field modulation of the metal-insulator transition was achieved. The observed field effects were discussed based on the strong interactions between carrier spins and localized spins in Mn ions, as well as the percolative mechanism of phase separation.     

Study on the Lorentz detuning and tuning of β=0.3, 352 MHz spoke cavity

The superconducting spoke cavity has been proposed to accelerate the proton in the low energy section of the high power proton linac for the Accelerator Driven Sub-critical System in China. In this paper, the basic geometric and RF parameters of a β=0.3, 352 MHz spoke cavity are given, and the Lorenz detuning and tuning are presented.     

Studies of some physical properties of PrFe0.7Ni0.3O3 thin films after 200 MeV Ag15+ irradiation

PrFe_0.7Ni_0.3O₃ thin films (thickness ~ 200 nm) were prepared by pulsed laser ablation technique on LaAlO₃ substrate. These films were irradiated with 200?MeV Ag¹⁵⁺ ions at various fluencies, ranging from 1 × 10¹¹ to 1 × 10¹² ions/cm². These irradiated thin films were characterized by using X-ray diffraction, dc conductivity, dc magnetization and atomic force microscopy. These films exhibit orthorhombic structure and retain it even after irradiations. The crystallite size (110–137?nm), micro strain (1.48 × 10^?2–1.75 × 10^?2 line^?2?m^?4) and dislocation density (79.7 × 10¹⁴–53.2 × 10¹⁴ line/m²) vary with ion fluencies. An enhancement in resistivity at certain fluence and then a decrease in its value (0.22175–0.21813?Ω?cm) are seen. A drastic change in observed magnetism after ion irradiation is seen. With ion irradiation, an increase in surface roughness, due to the formation of hillocks and other factors, is observed. Destruction of magnetic domains after irradiation can also be visualized with magnetic force microscopy and is in close agreement with magnetization data. The impact on various physical properties in these thin films after irradiation indicates a distortion in the lattice structure and consequently on single-particle band width caused by stress-induced defects.     

The quantum efficiency of the photo-electric effect in germanium for the 0.3–2 μ wavelength region

The absolute value of the quantum efficiency of the internal photoelectric effect in germanium in the 0.3–2 wavelength region was measured by means of the photovoltaic effect on a p-n junction. Two different regions were found. In the region from the infra-red absorption edge of germanium to a wavelength of 5750Å a practically constant number of electron-hole pairs, approximately equal to one, is produced per photon absorbed. In the second region from a wavelength of 5750Å and lower the number of generated pairs of current carriers is proportional to the total energy absorbed. In this region an energy of 2.5 eVis necessary to form an electron-hole pair.     

Photoproduction of positive pions from hydrogen at large angles in the energy range 0.3–2.0 GeV

The differential cross-section for the reaction γp↦π ⁺ n was measured using the bremsstrahlung beam of the Bonn 2.5 GeV electron synchrotron. The pions were detected and momentum analysed in a multichannel magnet spectrometer. Data reduction resulted in 1278 measured cross-sections which are presented as energy distributions at six laboratory angles between 180° and 95°. The range of laboratory photon energies extended from 0.3 to 2.1 GeV. The statistical accuracy is better than 3 percent, the systematic error is about 5 percent. The data are compared with other experimental results and predictions of a phenomenological analysis. These cross-sections are the result of a measurement program which was started in the seventies. Further results will be reported in forthcoming publications. Received: 2 February 2000 / Accepted: 14 August 2001     

Ultrafast optical probes of dynamic behavior in La0.7Sr0.3MnO3/YBa2Cu3O7 − δ/La0.7Sr0.3MnO3 heterostructure

Ultrafast pump-optical probe spectroscopy was used to analyze carriers dynamics behavior in La_0.7Sr_0.3MnO₃/YBa₂Cu₃O_{7 ? δ}/La_0.7Sr_0.3MnO₃ heterostructure. Our results show the pump signal ΔR/R for higher laser power (such as 21 and 41 mW), below T _c , first goes positive, then crosses zero and goes negative, before relaxing back to equilibrium over a time scale of a few ten picoseconds. We extract the characteristic relaxation time of the different process by fitting the data at these powers with a three-exponential decay. For higher laser power, the long characteristic relaxation time are obtained, which implies the competition between FM order and SC order in the La_0.7Sr_0.3MnO₃/YBa₂Cu₃O_{7 ? δ}/La_0.7Sr_0.3MnO₃ heterostructure.     

Measurement of the electric form factor of the neutron at Q2 = 0.3-0.8 (GeV/ c) 2 ⋆

The electric form factor of the neutron, G_E,n, has been measured at the Mainz Microtron by recoil polarimetry in the quasielastic D(¯e, e¯n)p reaction. Three data points have been extracted at squared four-momentum transfers Q ² = 0.3, 0.6 and 0.8 (GeV/c)². Corrections for nuclear binding effects have been applied.This revised version was published online in March 2005. In the previous version, the email address of one author was inadvertently assigned to multiple authors.     

Growth of Highly Conductive n-Type Al0.7Ga0.3N Film by Using AlN Buffer with Periodical Variation of Ⅴ/Ⅲ Ratio

High quality and highly conductive n-type Al0.7Ga0.3N films are obtained by using AlN multi-step layers （MSL） with periodical variation of Ⅴ/Ⅲ ratios by low-pressure metalorganic chemical vapour deposition （LP-MOCVD）. The full-width at half-maximum （FWHM） of （0002） and （1015） rocking curves of the Si-doped Al0.7Ga0.3N layer are 519 and 625 arcsec, respectively, Room temperature （RT） Hall measurement shows a free electron concentration of 2.9 × 10^19 cm^-3, and mobility of 17.8cm^2V^-1s^-1, corresponding to a resistivity of 0.0121 Ω cm. High conductivity of the Si-doped AlGaN film with such high Al mole fraction is mainly contributed by a remarkable reduction of threading dislocations （TDs） in AlGaN layer. The TD reducing mechanism in AlN MSL growth with periodical variation of Ⅴ/Ⅲ ratio is discussed in detail.