Study and optimal simulation of 4H-SiC floating junction Schottky barrier diodes’ structures and electric properties

This paper stuides the structures of 4H-SiC floating junction Schottky barrier diodes. Some structure parameters of devices are optimized with commercial simulator based on forward and reverse electrical characteristics. Compared with conventional power Schottky barrier diodes, the devices are featured by highly doped drift region and embedded floating junction layers, which can ensure high breakdown voltage while keeping lower specific on-state resistance, and solve the contradiction between forward voltage drop and breakdown voltage. The simulation results show that with optimized structure parameter, the breakdown voltage can reach 4.36 kV and the specific on-resistance is 5.8 mΩ·cm2 when the Baliga figure of merit value of 13.1 GW/cm2 is achieved.     

Theory study on a photonic-assisted radio frequency phase shifter with direct current voltage control

A photonic-assisted radio frequency phase shifter with direct current voltage control is proposed using a polymer- based integrated Mach-Zehnder modulator. A closed-form expression of radio frequency （RF） signal power and phase is given. Theoretical calculation reveals that by carefully setting the bias voltages, RF signal power variation lower than 1-dB and phase accuracy less than 3° can be achieved and are not degraded by perturbation of modulation index once the bias voltage drift is kept within -3% -- 3%.     

Dynamics of Vortex-Wave under a Travelling-Wave Modulation

The mechanism of destabilization is studied for the rotating vortices （scroll waves and spiral waves） in excitable media induced by a parameter modulation in the form of a travelling-wave. It is found that a rigid rotating spiral in the two-dimensional （2D） system undergoes a synchronized drift along a straight line, and a 3D scroll ring with its filament closed into a circle can be reoriented only if the direction of wave number of a travelling-wave perturbation is parallel to the ring plane. Then, in order to describe the behaviour of the synchronized drift of spiral wave and the reorientation of scroll ring, the approximate formulas are given to exhibit qualitative agreements with the observed results.     

Properties of Fraunhofer Diffraction by an Annular Spiral Phase Plate for Sidelobe Suppression

A simple and accurate method for calculating the optimal width of an annular spiral phase plate （SPP） to generate optical vortices with sidelobe suppression is proposed. The sideloSes can he sharply suppressed when the ratio of inner and outer radii of an annular SPP is equal to that of the principal ring and the first sidelobe diffracted by a circular SPP with the same topological charge n. Moreover, the ratio of the inner and outer radii of the optimal annular SPP depends only on the topological charge n and is not affected by the incident wavelength or the size of the SPP.     

Numerical Study on Open-Circuit Voltage of Single Layer Organic Solar Cells with Schottky Contacts: Effects of Molecular Energy Levels, Temperature and Thickness

We numerically investigate the effects of the exciton generation rate G, temperature T, the active layer thickness d and the position of LUMO level EL related to the cathode work function Wc at a given energy gap on the opencircuit voltage Voc of single layer organic solar cells with Schottky contact. It is demonstrated that open-circuit voltage increases concomitantly with the decreasing cathode work function Wc for given anode work functions and exciton generation rates. In the case of given cathode and anode work functions, the open-circuit voltage first increases with the exciton generation rate and then reaches a saturation value, which equals to the builtin voltage. Additionally, it is worth noting that a significant improvement to Voc could be made by selecting an organic material which has a relative high LUMO level （low ｜EL｜ value）. However, Voc decreases as the temperature increases, and the decreasing rate reduces with the enhancement of exeiton generation rate. Our study also shows that it is of no benefit to improve the open-circuit voltage by increasing the device thickness because of an enhanced charge recombination in thicker devices.     

Gate-to-body tunneling current model for silicon-on-insulator MOSFETs

A gate-to-body tunneling current model for silicon-on-insulator （SOl） devices is simulated. As verified by the mea- sured data, the model, considering both gate voltage and drain voltage dependence as well as image force-induced barrier low effect, provides a better prediction of the tunneling current and gate-induced floating body effect than the BSIMSOI4 model. A delayed gate-induced floating body effect is also predicted by the model.     

A two-dimensional analytical model for channel potential and threshold voltage of short channel dual material gate lightly doped drain MOSFET

An analytical model for the channel potential and the threshold voltage of the short channel dual-material-gate lightly doped drain （DMG-LDD） metal-oxide-semiconductor field-effect transistor （MOSFET） is presented using the parabolic approximation method. The proposed model takes into account the effects of the LDD region length, the LDD region doping, the lengths of the gate materials and their respective work functions, along with all the major geometrical parameters of the MOSFET. The impact of the LDD region length, the LDD region doping, and the channel length on the channel potential is studied in detail. Furthermore, the threshold voltage of the device is calculated using the minimum middle channel potential, and the result obtained is compared with the DMG MOSFET threshold voltage to show the improvement in the threshold voltage roll-off. It is shown that the DMG-LDD MOSFET structure alleviates the problem of short channel effects （SCEs） and the drain induced barrier lowering （DIBL） more efficiently. The proposed model is verified by comparing the theoretical results with the simulated data obtained by using the commercially available ATLASTM 2D device simulator.     

Low voltage substrate current： a monitor for interface states generation in ultra-thin oxide n-MOSFETs under constant voltage stresses

The low voltage substrate current （Ib） has been studied based on generation kinetics and used as a monitor of interface states （Nit） generation for ultra-thin oxide n-MOSFETs under constant voltage stress. It is found that the low voltage Ib is formed by electrons tunnelling through interface states, and the variations of Ib（△Ib） are proportional to variations of Nit （△Nit）. The Nit energy distributions were determined by differentiating Nit（Vg）. The results have been compared with that measured by using gate diode technique.[第一段]     

Low on-resistance high-voltage lateral double-diffused metal oxide semiconductor with a buried improved super-junction layer

A novel low specific on-resistance （Ron,sp） lateral double-diffused metal oxide semiconductor （LDMOS） with a buried improved super-junction （BISJ） layer is proposed. A super-junction layer is buried in the drift region and the P pillar is split into two parts with different doping concentrations. Firstly, the buried super-junction layer causes the multiple-direction assisted depletion effect. The drift region doping concentration of the BISJ LDMOS is therefore much higher than that of the conventional LDMOS. Secondly, the buried super-junction layer provides a bulk low on-resistance path. Both of them reduce Ron,sp greatly. Thirdly, the electric field modulation effect of the new electric field peak introduced by the step doped P pillar improves the breakdown voltage （BV）. The BISJ LDMOS exhibits a BV of 300 V and Ron,sp of 8.08 mΩ·cm2 which increases BV by 35% and reduces Ron,sp by 60% compared with those of a conventional LDMOS with a drift length of 15 μm, respectively.     

Experimental Study on Electrostatic with Two Guiding of Supersonic D20 Molecular Beam Charged Wires

We demonstrate the guiding of a supersonic heavy-water （D2O） molecular beam using a hollow electrostatic field generated by the combination of two parallel charged-wires and two grounded metal-plates, and report some new and preliminary experimental results. In the experiment, we detect the guiding signals by using the method of time-of-flight mass spectrum and study the dependence of the relative transmission of the beam guide on the guiding voltage. Our study shows that the relative transmission of the beam guide is increased linearly with increasing guiding voltage Vguid, and the number of the guided D20 molecules is at least increased by 89.4% when the guiding voltage is ＋20.0k V. Finally, some potential applications of our guiding scheme in the molecule optics are briefly discussed.     

Improvement of main drift chamber Monte-Carlo tuning model at BESⅢ

Based on real data, a new parameterized model of the main drift chamber response is proposed. In this model, we tune the ratio of good hits and the residual distribution separately. By data quality checking, the difference between simulation and data in track reconstruction e ciency reduces from 1% to 0.5% averagely for the pion in J/Ψ→π⁺π^-π⁰, and the momentum resolution agreement improves signi cantly for the proton in J/Ψ→pp.     

稀土离子Ho+,Ce+,La+与H2碰撞的单电子俘获截面测量

在复旦大学加速器实验室的３０ｋｅＶ同位素分离器上，使用新近建立的一套用于单价离子与气体分子碰撞的单电子俘获截面测量装置，测量了５—３０ｋｅＶ Ho⁺,Ce⁺,La⁺与H₂碰撞的单电子俘获截面．实验发现中空型离子源的阳极电压的变化对于稀土离子的亚稳态比例有一定影响，同时造成了单电子俘获截面的很大变化，而阳极电压对Ａｒ⁺的影响很小．还对实验结果进行了分析 关键词：     

Positive and Negative Pulse Etching Method of Porous Silicon Fabrication

We present a new method in which both positive and negative pulses are used to etch silicon for fabrication of porous silicon （PS） monolayer. The optical thickness and morphology of PS monolayer fabricated with different negative pulse voltages are investigated by means of reflectance spectra, scanning electron microscopy and photoluminescence spectra. It is found that with this method the PS monolayer is thicker and more uniform. The micropores also appear to be more regular than those made by common positive pulse etching. This phenomenon is attributed to the vertical etching effect of the PS monolayer being strengthened while lateral etching process is restrained. The explanation we propose is that negative pulse can help the hydrogen cations （H^＋） in the electrolyte move into the micropores of PS monolayer. These H^＋ ions combine with the Si atoms on the wall of new-formed micropores, leading to formation of Si-H bonds. The formation of Silt bonds results in a hole depletion layer near the micropore wall surface, which decreases hole density on the surface, preventing the micropore wall from being eroded laterally by F^- anions. Therefore during the positive pulse period the etching reaction occurs exclusively only at the bottom of the micropores where lots of holes are provided by the anode.     

Analysis of Three Annihilation Potential andp+ 12C Inelastic Scattering

The inelastic scattering of antiproton (p_lab=600MeV/c) by ¹²C leading to the excitation of the three normal parity T=0 levels is studied in the framework of Glauber model. The transition densities obtained from fitting to the electron scattering data and the three annihilation potentials derived from analysis of pp scattering data are used in the calculation. The inelastic angular distribution for exciting the three lowest normal parity T=0 states in ¹²C at 4.44MeV(J^π=2⁺), 7.66MeV(J^π=0⁺), and 9.63MeV(J^π=3^-) by 600MeV/c antiproton are calculated by selecting potential parameter suitably. The results are seen to be in fairly good agreement with the available experimental data. The results are given by using the elementary two-body amplitudes comparatively.     

A novel thin drift region device with field limiting rings in substrate

A novel thin drift region device with heavily doped N⁺ rings embedded in the substrate is reported, which is called the field limiting rings in substrate lateral double-diffused MOS transistor (SFLR LDMOS). In the SFLR LDMOS, the peak of the electric field at the main junction is reduced due to the transfer of the voltage from the main junction to other field limiting ring junctions, so the vertical electric field is improved significantly. A model of the breakdown voltage is developed, from which optimal spacing is obtained. The numerical results indicate that the breakdown voltage of the device proposed is increased by 76% in comparison to that of the conventional LDMOS.     

Above-Threshold Dissociation of HD+ in Femtosecond Laser Field

The above-threshold dissociation （ATD） of the HD＋ molecular ion in femtosecond laser field is investigated theoretically. The energy-dependent distribution of the dissociated fragments is calculated using an asymptoticflow expression in the momentum space. The calculations show that the ATD of HD＋ is sensitive to the initial vibrational level of ground electronic state. Multiphoton ATDs can be observed in the dissociation processes. The dynamics phenomena are interpreted by using the concept of light-dressed potential.     

A photon conversion finder at BESⅢ

A photon conversion finder (PCF) based on track information from the main drift chamber (MDC) of the Beijing Spectrometer (BES0) at the Beijing Electron Positron Collider (BEPC/) is developed. The validation of the PCF is done by reconstructing π⁰ and measuring the branching fraction of J/ψ →γη'. Using the developed PCF tool, we mapped the materials from the interaction point through the BEPCII beam pipe up to the inner wall of the MDC.     

Secondary Collision and the Enhancement of the K+π+ Ratio in the High Energy Heavy-ion Collision

The enhancement of K⁺/π⁺ ratio in the high energy heavy-ion collision is believed to be a possible signature of the quark gluon plasma.Based on the Participant Nucleon Model and the concept of the formation time of secondary particles,the K⁺/π⁺ ratio in the central collision of Si(14.5GeV/c) and Au are calculated by Monte Carlo simulation.The following secondary collisions are considered.πN→K⁺Y、ππ→KK and the single charge exchange reaction between pions and nucleons.The calculation results show that the increased K⁺/π⁺ ratio caused by these secondary collisions is not enough to explain the experimental data observed by the E802 group at BNL.     

A Simple Analytic K+N Two-Body Potential

The K⁺N two-body potential is calculated in the framework of the constituent quark model.The derived potential includes the central and spin-orbit contributions with a simple analytic form.The K⁺N scattering phase shifts are calculated and compared with experimental data.The results show that the potential can provide reasonable good explanation for the K⁺N data,particularly for the large phase shift of P-wave I=0,J=1/2channel.