部分屏蔽多极电子鎗聚焦问题

本文对于在有磁场下多阳极电子鎗的电子注聚焦问题进行了理论分析。阴极处磁场可以具有任意屏蔽程度,得到了在加速场内描写电子轨迹的傍轴方程的解析解。在理论分析中,考虑了包括空间电荷效应的情况。     

电子束在周期场中的稳定性

本文讨论了强流电子束通过周期性静电场和静磁场的稳定性。说明了圆柱形电子束通过简谐电磁场和周期性非简谐场例如锯齿形,矩形,等腰梯形等静电场的稳定和不稳定区域。将各种场的主要不稳定区进行比较,表明锯齿形场的主要不稳定区宽度最小。指出当空间电荷效应不可略去时,电子束在稳定区内并不是无条件稳定而是有条件稳定的。这与空间电荷电流大小以及电子束的振幅有关。     

Radiation-induced 1/f noise degradation of PNP bipolar junction transistors at different dose rates

It is found that ionizing-radiation can lead to the base current and the 1/f noise degradations in PNP bipolar junction transistors. In this paper, it is suggested that the surface of the space charge region of the emitter-base junction is the main source of the base surface 1/f noise. A model is developed which identifies the parameters and describes their interactive contributions to the recombination current at the surface of the space charge region. Based on the theory of carrier number fluctuation and the model of surface recombination current, a 1/f noise model is developed. This model suggests that 1/f noise degradations are the result of the accumulation of oxide-trapped charges and interface states. Combining models of ELDRS, this model can explain the reason why the 1/f noise degradation is more severe at a low dose rate than at a high dose rate. The radiations were performed in a Co~(60) source up to a total dose of 700 Gy(Si). The low dose rate was 0.001 Gy(Si)/s and the high dose rate was 0.1 Gy(Si)/s. The model accords well with the experimental results.     

利用Monte Carlo法计算粒子传输中的空间电荷效应

在电子束印刷(electron-beam lithography)、聚焦离子束(focus ion beam)以及阴极射线管(cathode ray tube)等电子及离子束器件中,束中各粒子之间存在相互作用,产生空间电荷效应。人们对电子及离子束器件中的空间电荷效应已经做了大量的研究。到目前为止,通常采用Monte Carlo法计算粒子输运过程中的离散的空间电荷效应。在此主要研究在束形成区利用Monte Carlo法计算空间电荷效应,并讨论在计算过程中出现的边缘效应,在此基础上提出一些新的处理方法以减小边缘效应,提高计算效率。     

EFFECT OF SPACE CHARGE ON THE FREQUENCY OF OSCILLATION IN POSITIVE-GRID OSCILLATORS

In estimating the frequency of oscillation of a positive-grid oscillator, it isusually assumed that the space charge effect is negligible. Under this assumption, the potential distribution in the space between the plane-parallel electrodes is linear. Thus the electric field in the space is uniform and the average velocity of electrpn flight can be used to evaluate the frequency of oscillation. The presence of space charge affects the potential distribution in space so that the electric field in this region is no more constant. Hence more exact formula must be used to compute the frequency of oscillation. The calculation is further complicated by the fact that the anode potential is usually made slightly negative with respect to the cathode. In this case, the location of the virtual cathode at which the electrons turn back does not coincide with that if a straight line potential distribution were assumed. The predicated trequency of oscillation is about 10-20 percent lower than that if space charge were neglected.     

相对论电子束虚阴极静电振荡的粒子模拟

本文运用有限大小粒子模型,用等离子体粒子模拟方法,对相对论电子束的虚阴极振荡作了一维静电粒子模拟。结果表明,在注入电流小于空间电荷极限电流时,电子束能稳定传输并能全部通过。当注入电流超过空间电荷极限电流时,传输是不稳定的,将有部分电子反射,部分通过。空间电荷形成的虚阴极的位置和电势周期性地振荡。电流越大,虚阴极位置越靠近注入面且变化范围越小,虚阴极电势越低且振幅越大,振荡频率越高且大于电子束等离子体频率。     

Nonequilibrium mechanisms of weak electrolyte electrification under the action of constant voltage

The formation of space charge in weak electrolytes, specifically in liquid dielectrics, has been considered. An analytical solution is given to a simplified set of Nernst–Planck equations that describe the formation of nonequilibrium recombination layers in weak electrolytes. This approximate analytical solution is compared with computer simulation data for a complete set of Poisson–Nernst–Planck equations. It has been shown that the current passage in weak electrolytes can be described by a single dimensionless parameter that equals the length of a near-electrode recombination layer divided by the width of the interelectrode gap. The formation mechanism and the structure of charged nonequilibrium near-electrode layers in the nonstationary regime have been analyzed for different injection-to-conduction current ratios. It has been found that almost all charge structures encountered in weak dielectrics can be accounted for by the nonequilibrium dissociation–recombination mechanism of space charge formation.     

(n)nc-Si：H/(p)c-Si异质结中载流子输运性质的研究

采用常规等离子体增强化学气相沉积工艺,以高H₂稀释的SiH₄作为反应气体源和PH₃作为磷原子的掺杂剂,在p型(100)单晶硅((p)c-Si)衬底上, 成功地生长了施主掺杂型纳米硅膜((n)nc-Si:H),进而制备了(n)nc-Si:H/(p)c-Si异质结,并在230—420Ｋ温度范围内实验研究了该异质结的Ｉ-Ｖ特性.结果表明,(n)nc-Si:H/(p)c- Si异质结为一典型的突变异质结构,具有良好的温度稳定性和整流特性.正向偏压下 关键词： (n)nc-Si:H/(p)c-Si异质结 能带模型 电流输运机构 温度特性     

THE PROCESS OF SPACE CURRENT NEUTRALIZATION OF INTENSE RELATIVISTIC ELECTRON BEAM UNDER AN EXTERNALLY APPLIED MAGNETIC GUIDE FIELD

The process of space current neutralization of intense relativistic electron beam under an externally applied magnetic guide field is discussed in this paper. Ionization by electron avalanching and by beam electrons impact and recombination is included in the calculation of plasma density buildup, with plasma heating by return current and two- stream instability taken into account. A code to evaluate the process of space current neutralization was set up. The calculations demonstrate that the optimum gas pressure increases as peak beam current increases and it decreases as the risetime of beam pulse increases.     

TWO-DIMENSIONAL NUMERICAL SIMULATION OF LOW FREQUENCY OSCILLATIONS OF SPACE CHARGE AND POTENTIAL IN THE GYROTRON ADIABATIC TRAP

The development of oscillations of the space charge and potential in the adiabatic trap of a gyrotron between the cathode and the cavity is studied numerically. The PIC method is applied, with the real two-dimensional distributions of the electric and magnetic fields taken into account. Secondary emission is included into the numerical model, as well as such factors as the electron beam space charge, thermal velocities of electrons, and emitter roughness. The value of the trapped space charge as a function of time is calculated. Time dependences of the potential in various cross-sections of the formation system are traced. The amplitudes of its variable component have been found and then the corresponding frequency spectra have been calculated. The process of cathode bombardment is investigated. The energy distribution and time dependence of the current in the electron beam coming to the operating space are found. Some ways to reduce the oscillations of the potential and the space charge are discussed.     

Current transport in ZnO/Si heterostructure grown by laser molecular beam epitaxy

The n-ZnO/p-Si heterojunction was fabricated by depositing high quality single crystalline aluminium-doped n-type ZnO film on p-type Si using the laser molecular beam epitaxy technique. The heterojunction exhibited a good rectifying behavior. The electrical properties of the heterojunction were investigated by means of temperature dependence current density-voltage measurements. The mechanism of the current transport was proposed based on the band structure of the heterojunction. When the applied bias V is lower than 0.15 V, the current follows the Ohmic behavior. When 0.15V 0.6 V), the space charge limited effect becomes the main transport mechanism. The current-voltage characteristic under illumination was also investigated. The photovoltage and the short circuit current density of the heterojunction aproached 270 mV and 2.10 mA/cm 2 , respectively.     

Multi-layer ambipolar light-emitting organic field-effect transistors

Mutli-layer light-emitting organic field-effect transistors (OLETs) are shown to have high internal quantum efficiencies approaching 5%, a value much higher than the conventional organic light-emitting diodes (OLEDs). This work re-examines some data reported in the literature on OLETs and put forward a model that explains the charge transport and light emission process. Our analyses suggest that the reported improvements on the internal quantum efficiency of OLETs are directly linked to charge recombination and light emission and is independent of the drain-source current as well as the gate-induced charge density in the accumulation layer. Such independence allows the internal quantum efficiency to increase as the drain-source current decreases. The process differs from the charge transport in OLEDs where recombination and light emission are directly tied to the injected space charge densities thereby preventing the internal quantum efficiency of OLEDs to increase even when the device current is lowered.     

DERIVATION OF THE LEHNERT FIELD EQUATIONS FROM GAUGE THEORY IN VACUUM: SPACE CHARGE AND CURRENT

It is shown that the Lehnert field equations in vacuum, with concomitant space charge and current, can be derived straightforwardly from standard gauge theory applied in vacuum, using the concept of covariant derivative and Feynman's universal influence. The Lehnert and Proca field equations are shown to be inter-related through the well-known de Broglie theorem, in which the photon mass can be interpreted as finite. These ideas go some way towards addressing the inconsistency inherent in Maxwell's famous displacement current, which has no concomitant vacuum space charge.     

强流重离子束在轴对称电场中的温度和能量展宽

本文研究带电粒子束在轴对称电场(包含束空间电荷平均场)中的温度和能量展宽,所得结果表明,在漂移区内,此种能量展宽与束电流成正比,与束的宏观流动速度成反比,因此,对于强流重离子束而言,此种能量展宽在总的能量展宽中将起重要的作用,若束能为20keV,束流为20mA,在漂移区中,¹H离子束的能量展宽为26.5eV,而相同条件下的¹²¹Sb离子束则为291.5eV,而且随束流增加线性上升,本文对束温度的研究结果表明,在漂移区中,束空间电荷效应使束温度增加。 关键词：     

Development of ZnTe film with high copper doping efficiency for solar cells

Since a hole barrier was formed in back contact due to mismatch of work function, the back contact material for CdTe cell has been a significant research direction. The ZnTe:Cu is an ideal back contact material, which reduces the valence band discontinuity and can be used as the electron back reflection layer to inhibit interface recombination. The conductivity of ZnTe:Cu film is improved by applying RF-coupled DC sputtering and post-deposition heat treatment. The doping efficiency is computed as the ratio of free hole density and copper concentration, which can be correlated with performance for CdTe-based solar cell. The higher doping efficiency means that more copper atoms substitute for Zn sites in ZnTe lattices and less mobilized copper atoms remain which can enter into the CdTe absorber layer. Copper atoms are suspected as dominant element for CdTe-based cell degradation. After optimizing the ZnTe:Cu films, a systematic study is carried out to incorporate ZnTe:Cu film into CdTe solar cell. The EQE spectrum is kept relatively stable over the long wavelength range without decreasing. It is proved that the conduction band barrier of device with ZnTe:Cu/Au contact material has an effect on the EQE response, which works as free electron barrier and reduces the recombination rate of free carrier. According to the dark J—V data or the light J—V data in the linear region, the current indicates that the intercept gives the diode reverse saturation current. The results of ideality factor indicate that the dominant recombination occurs in the space charge region. In addition, the space charge density and depletion width of solar cell can be estimated by C—V profiling.     

STUDIES OF THE FOCUSING PROPERTIES OF A SPACE CHARGE LENS

A space charge lens has been designed and tested which can be used to focus intense ion beams at several tens of keV. The experimental results obtained can be interpreted with a simplified physical model. The existence of a space charge field and its strong focusing properties are tested experimentally. And it is shown that the relaxation time for the formation of space charge field is much less than 10 μs under our experimental conditions, thus the lens can be used to focus pulsed beams with length of several hundereds of μs of longer.     

Photoelectronic and electrical properties of Tl2InGaS4 layered crystals

Tl₂InGaS₄ layered crystals are studied through the dark electrical conductivity, space charge limited current and illumination- and temperature-dependent photoconductivity measurements in the temperature regions of 220-350 K, 300-400 K and 200-350 K, respectively. The space charge limited current measurements revealed the existence of a single discrete trapping level located at 0.44 eV. The dark electrical conductivity showed the existence of two energy levels of 0.32 eV and 0.60 eV being dominant above and below 300 K, respectively. The photoconductivity measurements reflected the existence of two other energy levels located at 0.28 eV and 0.19 eV at high and low temperatures, respectively. The photocurrent is observed to increase with increasing temperature up to a maximum temperature of 330 K. The illumination dependence of photoconductivity is found to exhibit supralinear recombination in all the studied temperature ranges. The change in recombination mechanism is attributed to exchange in the behavior of sensitizing and recombination centers.     

半导体深能级瞬态谱中多子脉冲下的少子陷阱响应

在一个Si中掺Aup⁺n结的多子脉冲下深能级瞬态谱(DLTS)中,发现了一个少子峰信号。给出了这一现象的主要实验结果,并做了系统的物理分析。这是p⁺n结中高掺杂一侧的自由少数载流子尾在自建势所张开的空间电荷区中被少子陷阱俘获后,再发射的结果。 关键词：     

Structure and transport mechanisms of Si/porous Si n-p junctions prepared by liquid phase epitaxy

Heterojunction devices of n-Si/p-PSi were fabricated by growing n-Si films onto p-type porous Si substrates by liquid phase epitaxy. The structure of the grown films was checked using scanning electron microscopy and X-ray diffraction spectroscopy. X-ray diffraction measurements showed that the grown films have monocrystalline structure oriented along (1 1 1) direction with mainly cubic phase. Current-voltage (I-V) and capacitance-voltage (C-V) characteristics were measured over the temperature range from 298 to 398 K. The analysis of the dark I-V characteristics of n-Si/p-PSi at several temperatures is done to elucidate the conduction mechanisms and the evaluation of the heterojunction parameters is presented. Two carrier transport mechanisms are believed to be at the origin of the forward current. At low bias voltage (V ≤ 0.4 V) the forward current is dominated by the recombination at the porous silicon side of the space charge region. In the 0.5 V ≤ V ≤ 1.4 V region, the current transport is due to the space charge—limited current mechanism dominated by a single trapping level of energy 0.41 eV. The reverse current is considered to be mainly generated in the depletion region of the porous silicon. The capacitance-voltage results confirm an abrupt junction with a homogenous distribution of the impurities inside the space charge region. Information on the depletion region, built-in voltage and net carrier concentration were obtained from the dark C-V characteristics.     

Temperature dependence of dc photoconductivity in CdTe thin films

The temperature dependence of dc photoconductivity in the measuring range 303–417 K has been studied in CdTe thin films having thicknesst < 4000 Å. The photoactivation energy decreases in dark which is explained on the basis of grain boundary (GB) effect. The current lost to recombination at GB space charge region causes a negative effect on the photosensitivity of the films. A decrease in photosensitivity with increase in temperature is attributed to the reduction of photoexcitation process. It is observed that the minority carrier lifetime varies inversely with light intensity which supports the sublinear relationship of photoconductivity with the intensity of light and thereby confirms the defect-controlled photoconductivity in CdTe thin films