Biaxially aligned YBCO film tapes fabricated by all pulsed laser deposition

Biaxially aligned yttria-stabilized zirconia (YSZ) films on Ni-based alloy substrates were realized with high deposition rate of 0.5 μm min⁻¹ by the inclined substrate deposition (ISD) technique without ion beam assistance. The microstructure of YSZ was examined to study the growth mechanism of biaxial alignment by ISD. Columnar structures toward the plasma plume suggested a self-shadowing effect in the ISD process. To raise I_c values, YBCO thickness was increased up to 5 μm. Thick YBCO films with high J_c values were realized on the ISD-grown YSZ. Long YBCO tapes with biaxial alignment were successfully fabricated using continuous pulsed laser deposition and a high I_c value of 37.0 A (77.3 K, 0 T) at a 75 cm voltage tap spacing was achieved.     

The measurement of penetration depth and surface resistance of bulk YBCO superconductor by using microstrip resonator method

We have measured the resonance curves of a high Tc superconducting microstrip resonator at both room temperature and liquid nitrogen temperature, and done same thing to a copper microstrip resonator with the same width and length as high Tc superconducting microstrip resonator. These four curves have been compared with each other. After that we obtained the penetration depth and surface resistance of high Tc superconductor at liquid nitrogen temperature. The microstrip resonator method has the advantage of simple. The results agree with theoretical prediction and other papers quite well.     

Macroscopic numerical evaluation of heat generation in a bulk highTc superconductor during pulsed field magnetization

Pulsed-field magnetization of a bulk high Tc superconductor (HTS) is evaluated by using a macroscopic numerical simulation code. Local heat generation in the HTS during the pulsed-field magnetization is discussed to clarify the dynamic magnetization process. Nonlinear dependence of shielding current on the dynamic magnetic field is considered by using the flux flow-creep model. Dependence of flow resistivity on the magnetic field and temperature are also evaluated with the Bardeen-Stephen and the Tinkham models. It is numerically confirmed that reported experimental results are due to a decrease of the shielding current caused by local heat generation     

A new planar injection-gated bulk switching device based upon deep impurity trapping

Under the proper conditions, double-injection (DI) diodes with partially compensated deep impurities will exhibit "S"-type switching characteristics similar to conventional silicon-controlled rectifiers (SCR's). A practical injection-gating scheme has been achieved for the first time in a planar configuration to control the switching behavior of these devices, marked by extreme sensitivity of the gate over a range of switching voltages. An experiment to demonstrate the feasibility of these devices for practical application is described. Finally, a phenomenological explanation is presented for the gate-controlled switching of these devices.     

Effects of bulk trapping on the memory characteristics of thick-oxide MNOS variable-threshold capacitors

Charge-storage measurements have been performed at room temperature on thick-oxide MNOS structures using on automatic measuring system which allows a detailed and quite accurate investigation of the hysteresis loops (flat-band voltage versus stress voltage characteristics) of such devices. The experimental data have revealed several anomalous features, previously unreported in the literature, which are very general properties of double-layer devices. It is found that the initial hysteresis loop of a virgin device is very similar to the ‘conventional’ hysteresis loop, with flat bottoms and tops and steeply-rising sides. However, the second and subsequent hysteresis loops show dramatic changes in the flat-band voltage in the formerly flat regions. The results are interpreted in a selfconsistent manner, in terms of trapping phenomena throughout the bulk of both insulator regions. The trapped charge is found to produce strong internal fields that cause redistribution of the trapped charge in both the nitride and the oxide; it is these trapping effects which lead to the dramatic changes in the hysteresis loops after the initial pulse sequence. The existence of trapping levels in the bulk of the nitride is a necessary extension of the idealized model in which trapping levels are assumed to exist only at the oxide-nitride interface.     

Enhanced photoconductivity and trapping rate through control of bulk state in organic triphenylamine-based photorefractive materials

In organic optical semiconductors, it is rather challenging to achieve precise control of photoconductivity and charge trapping, which determines the device performance. This paper reports on enhanced photorefractive response rate through control of the photoconductivity and trapping rate in organic triphenylamine-based photorefractive materials by means of bulk state tuning. The bulk state in organic triphenylamine-based photorefractive composites was controlled through a rapid cooling process from various melting temperatures during sample fabrication. The photoconductivity and trapping rate were determined from photocurrent measurements. Fabrication at lower melting temperatures enhanced the trapping rate for deep traps, whereas it reduced the trapping rate for shallow traps. As a result, a faster photorefractive response was obtained.     

Interpretation of surface and bulk effects using the pulsed MIS capacitor

The interpretation of lifetimes and surface generation velocities determined from pulsed MIS-C measurements is examined. The effect of surface generation on the C-t response and ‘Zerbst’ plot is demonstrated and values for s₀ are correlated with the density of fast surface states. Different kinds of surface dominated responses are analyzed and we discuss how the bulk characteristics can be retrieved. It is also shown that pulsing from inversion significantly lowers s₀, but for high densities of surface states this technique does not suffice to eliminate surface effects. Finally, an approximate analysis of the C-t data is shown to agree quite well with the more exact analysis and it is then applied to lifetime maps of Si wafers.     

An improved analytical model of 4H-SiC MESFET incorporating bulk and interface trapping effects

An improved analytical model for the current-voltage (I-V) characteristics of the 4H-SiC metal semiconductor field effect transistor (MESFET) on a high purity semi-insulating (HPSI) substrate with trapping and thermal effects is presented. The 4H-SiC MESFET structure includes a stack of HPSI substrates and a uniformly doped channel layer. The trapping effects include both the effect of multiple deep-level traps in the substrate and surface traps between the gate to source/drain. The self-heating effects are also incorporated to obtain the accurate and realistic nature of the analytical model. The importance of the proposed model is emphasised through the inclusion of the recent and exact nature of the traps in the 4H-SiC HPSI substrate responsible for substrate compensation. The analytical model is used to exhibit DC I-V characteristics of the device with and without trapping and thermal effects. From the results, the current degradation is observed due to the surface and substrate trapping effects and the negative conductance introduced by the self-heating effect at a high drain voltage. The calculated results are compared with reported experimental and two-dimensional simulations (Silvaco^®-TCAD). The proposed model also illustrates the effectiveness of the gate-source distance scaling effect compared to the gate-drain scaling effect in optimizing 4H-SiC MESFET performance. Results demonstrate that the proposed I-V model of 4H-SiC MESFET is suitable for realizing SiC based monolithic circuits (MMICs) on HPSI substrates.     

粒子在单束激光势阱中的束缚力

本文在几何光学近似下,考虑到强聚焦高斯光束的结构,导出了TEM_(oo)高斯光束对透明球状粒子作用力的计算公式,数值计算给出了单束激光阱存在的条件,并讨论了光吸收的影响。     

一种新型环形上DBR刻蚀微结构VCSEL及其空心光束（英文）

设计了带有质子注入高阻区的刻蚀微结构面发射半导体激光器结构,使得从出光口到上DBR形成环形波导,进而直接产生空心激光束输出。使用FDTD软件计算了刻蚀微结构VCSEL的光场分布,得到的环形模式图样在不同模式数目下都能保持空心光束的特性。制备了室温下激射波长为848 nm的微结构VCSEL,并测试其输出特性。阈值电流为0.27 A,峰值功率最高可达170 mW。不同电流下的近场图都显示出非常明显的空心环形光斑,远场光强分布曲线也符合空心光束的特性。该新型VCSEL技术为空心光束甚至阵列器件的发展提供了一种新的方法。     

Bit error rate experiments in ring-shaped RSFQ circuits

Ring-shaped rapid single flux quantum (RSFQ) circuits composed of segments of Josephson transmission lines (JTLs) and other RSFQ circuits enable permanent SFQ pulse circulation. New ring structures of different designs have been realized which comprise T-flipflop (TFF) and multiplier (MULT) circuits. Reliability in circuit operation has been proven experimentally by a bit error rate BER≅10⁻¹⁶. The fabrication process has been optimized by using PTB-4 μm Nb/Al₂O₃–Al/Nb trilayer technology with externally shunted tunnel junctions of critical current densities of j_c=≅1 kA/cm². Characteristic voltage is V_c=250 μV and Steward–McCumber parameter β_c≤1. A linear dependence of pulse circulation frequency on JTL bias currents has been measured within a bias current interval of 20%.     

A quick method for the determination of bulk generation lifetime in semiconductors from pulsed MOS capacitance measurements

The high frequency capacitance transient that is observed when an MOS (Metal-Oxide-Semiconductor) capacitor is pulsed from accumulation to deep depletion condition is usually analysed graphically to determine the values of bulk generation rates or of minority carrier lifetimes in the semiconductor concerned. However, this analytical process is a long and laborious one and in this paper a quicker method for the determination of lifetime is suggested. The extracted lifetime value is typically within 10% of the true value and is sufficient for applications such as on-line process control.     

Carrier-recombination statistics in a 2-level trapping system

When there is substantial interaction between two trap levels in the band gap, the carrier recombination in the depletion layer of a silicon p?n junction does not follow conventional Shockley?Read?Hall statistics. Such a system is capable of producing a current/voltage relationship approximating to the form I? exp (eV/1.5 kT).     

Flux Distribution in a Linear Magnetic Shield

The two-dimensional flux distribution in a magnetic shield of constant permeability and conductivity is presented in a series of magnetic vector-potential contour plots. The plots show the leakage-flux tubes in the shield and in the shielded region. Three- dimensionless parameters representing the shielding 1) thickness, 2) skin depth, and 3) permeability are introduced as the flux-distribution variables. The induced eddy currents cause the resulting fields in the shield to be elliptically polarized and to break into a characteristic cell structure which increases in complexity with rising frequency.     

聚焦部分相干平顶涡旋光束对瑞利粒子的捕获

基于广义惠更斯-菲涅尔原理和瑞利散射理论,推导了聚焦部分相干平顶涡旋(partially coherent flat-topped vortex, PCFTV)光束作用在瑞利微粒上辐射力的表达式,主要研究聚焦PCFTV光束对不同折射率的两种粒子的捕获情况。研究结果表明,聚焦PCFTV光束可以在焦点处捕获高折射率和低折射率的粒子。随着光束阶数的增大以及相关长度的减小,光束对微粒的捕获能力增强。所得结果对PCFTV光束应用于光学操控具有一定的意义。     

Microwave amplification in a GaAs bulk semiconductor

Continuous linear microwave amplification has been obtained usingn-type GaAs at room temperature. Amplification of signals in the 2 to 10 Gc/s range occurred when a dc field applied across semiconductor wafers mounted in a conventional reflection type amplifier circuit exceeded about 3100 volts/cm. Ohmic contacts were applied to wafers 125 µ square and 40 to 120 µ thick. The resistivity varied between 10 and 120 ohm-era. Then cdot Lproduct in amplifying samples did not exceed 5.10¹¹cm^-2. The conductance measured in the 1 to 10 Gc/s region was found in some samples to be negative over a frequency range of one octave. Other samples exhibited negative conductance (i.e., gain) only over a few hundred megacycles. Each sample showed a peak gain accompanied by a range of absorption at the high-frequency end of the negative conductance region. The differential conductance at dc was positive. An amplifier noise figure of 23 dB was measured using 120 ohm-era GaAs at 10 dB gain and 1 dB of gain compression occurred when the output power level reached -6 dBm.     

HF and DF laser action by a pulsed microwave discharge

A pulsed electrodeless microwave discharge withE-field enhancement by a tapered waveguide has been employed to produce HF and DF laser radiation from premixtutes of SF6+ H6and SF6+ D2. The 720 patm (690 patm) HF (DF) laser had an average multiline output power of 6 mW (1 mW) for an efficiency of 0.1 percent (0.02 percent) while operating at 1 kHz (450 Hz) pulse-repetition frequency (PRF). The HF (DF) laser was operated at reduced output power and efficiency up to 4.2 kHz (2.5 kHz) PRF. Reduced HF laser efficiency was obtained when C3H8was substituted for H2.     

Light bullets formation in a bulk media

The conditions for the formation of a light bullet pulse, propagating with nearly constant spatial and temporal parameters in a bulk nonlinear medium, are obtained. A pump and probe pulse configuration using an induced phase modulation (IPM) is used. The IPM effect provides a well-controllable spatial and temporal trapping of the probe pulse. The authors derive analytical expressions for the critical parameters of the system, incorporating input power, pulse duration, pump and probe beam radii, medium parameters, etc. The system parameters analyzed are rather general and include varying pump and probe pulse durations and delay. The constant parameters of the light formation are shown to be limited by the walk-off effect. An analytical balance condition is obtained for the spatial and temporal soliton-like formation