石墨烯p-n结在磁场中的电输运热耗散

石墨烯是一种特殊的二维材料,其独特的能带结构允许人们通过电场来调控其载流子的类型和浓度,因此,在构建双极型纳米电子器件方面具有潜在应用前景.本文基于紧束缚格点模型,利用非平衡格林函数方法及Landauer-Büttiker公式,研究了石墨烯p-n结在磁场中的电输运热耗散问题.在强磁场作用下,结的两边均处于量子霍尔相,存在拓扑保护的手性边缘态.直觉上,这种拓扑保护的手性边缘态应当是无热耗散的.但本文研究发现,当有耗散源时,尽管手性边缘态受到拓扑保护,热耗散却依然可以发生.对于完美的石墨烯,单极结输运时热耗散发生在体系边缘;偶极结输运时在体系边缘和结的界面处均可以发生热耗散.当无序存在时,无论单极结还是偶极结,无序均能增强热耗散.此外,本文还研究了不同位置处的电子能量分布,发现热耗散是否发生只取决于电子是否处于非平衡分布.这些结果表明拓扑只能保护电子的传播方向,却不能禁止热耗散的发生.     

光阴极电子枪的研究

一、光阴极的研究进展情况 1.问题的提出 在发展FEL的过程中,对电子束的品质提出了很苛刻的要求,而束流品质是用亮度来表征的,规一化峰值亮度定义为:     

光阴极RF腔注入器

 光阴极RF腔注入器是一种强流、窄脉冲(ps量级)、低发射度的电子束源。文章给出了CAEP光阴极RF腔注入器的结构和实验结果,结构主要包括驱动激光器、Cs₂Te阴极制备室、2.5个RF腔、高功率微波源和测量仪器等,其中驱动激光器的参数是影响注入器电子束质量的重要因素;实验上,该光阴极RF腔注入器可稳定输出能量2MeV、流强70A、发射度～4mm.mrad的高亮度电子束流。     

光阴极注入器的驱动激光器

光阴极注入器要求驱动激光器的激光时间抖动小、脉冲宽度窄、激光波长短和脉冲功率高。从原理和实验上介绍光阴极注入器的驱动激光器,包括连续波锁模振荡腔、时间同步,激光脉冲功率放大等;该激光器输出激光微脉冲宽度10ps,微脉冲时间抖动小于2ps,宏脉冲宽度2.5 μs, 峰值功率100kW, 已用于光阴极RF腔注入器实验,并获得了很好的结果。     

光阴极注入器的驱动激光器

 光阴极注入器要求驱动激光器的激光时间抖动小、脉冲宽度窄、激光波长短和脉冲功率高。从原理和实验上介绍光阴极注入器的驱动激光器,包括连续波锁模振荡腔、时间同步,激光脉冲功率放大等;该激光器输出激光微脉冲宽度10ps,微脉冲时间抖动小于2ps,宏脉冲宽度2.5 μs, 峰值功率100kW, 已用于光阴极RF腔注入器实验,并获得了很好的结果。     

基因算法在光阴极注入器优化设计中的应用

基于正在建设的大连自由电子激光装置,研究了基因算法在注入器优化设计中的系统应用。与传统的注入器优化方法相比较,基因算法在多变量、多目标注入器优化问题中具有优化效率高、优化结果精确的优势;通过采用权重因子的方法将多目标问题转化为单目标优化问题,大大简化了基因算法优化流程;光阴极注入器对束流稳定性要求严格,通过基因算法优化使束流的到达时间抖动控制到150fs,满足束流稳定性的要求。     

基因算法在光阴极注入器优化设计中的应用

基于正在建设的大连自由电子激光装置,研究了基因算法在注入器优化设计中的系统应用。与传统的注入器优化方法相比较,基因算法在多变量、多目标注入器优化问题中具有优化效率高、优化结果精确的优势;通过采用权重因子的方法将多目标问题转化为单目标优化问题,大大简化了基因算法优化流程;光阴极注入器对束流稳定性要求严格,通过基因算法优化使束流的到达时间抖动控制到150 fs,满足束流稳定性的要求。     

不同Cs、O电流比激活对GaAs光阴极灵敏度和稳定性的影响

鉴于不同的铯氧电流激活GaAs光阴极时会对激活过程和结果产生不同的影响,从而影响GaAs光阴极的灵敏度和稳定性.以固定铯源电流,改变氧源电流的方式获取不同铯、氧电流比,激活同类GaAs光阴极,得到了3组实验数据.对数据进行分析,结果表明:同类光阴极在相同条件下激活时,光电流出现的时间几乎一致,并且首个光电流峰值也非常接近;激活时ICs/IO=1.07是目前获得高灵敏度、高稳定性GaAs光阴极的最佳电流比,而ICs/IO=1.10时光阴极灵敏度低但稳定性好,ICs/IO=1.03时光阴极灵敏度高但稳定性差.双偶极层模型认为Cs、O激活后GaAs表面形成了稳定均匀的GaAs-O-Cs:Cs-O-Cs双偶极层,并达到了负电子亲和势,这一点与实验数据的分析结果相一致.该方法可用于提高GaAs光阴极灵敏度和稳定性.     

硅p-n结太阳电池对DF激光的响应

 对硅p-n结太阳电池在DF激光辐照下的响应进行了理论和实验研究。推导了p-n结反向饱和电流随温度的近似变化关系。根据该近似关系,计算了太阳电池在DF激光辐照过程中输出电压的变化曲线。计算结果和实验结果之间取得了比较好的一致性。     

硅p-n结太阳电池对DF激光的响应

对硅p-n结太阳电池在DF激光辐照下的响应进行了理论和实验研究。推导了p-n结反向饱和电流随温度的近似变化关系。根据该近似关系,计算了太阳电池在DF激光辐照过程中输出电压的变化曲线。计算结果和实验结果之间取得了比较好的一致性。     

Solar cells

Solar cells are based on the photovoltaic effect of converting solar energy into electric energy. The mechanism for solar cells is divided into steps, that is, electron-hole pair generation by absorption of light in semiconductors, separation of electron-hole pairs by built-in potential, electron-hole recombination, collection of charge carriers by metal electrodes, etc. In this article, the principle and the theories of these basic steps are presented. On the basis of these steps, methods to improve the efficiency for solar cells are discussed. The fabrication process and the situation of currently produced solar cells are also presented. Solar cells having no p-n junction, that is, photoelectrochemical solar cells and MIS solar cells, are discussed from the perspective of low-cost solar cells.     

超高真空系统中GaAlAs光电阴极的重新铯化研究

为了探索在超高真空系统中使用稳定性和重复性好的光电阴极,开展了金属有机化学气相沉积生长的反射式GaAlAs和GaAs光电阴极的激活实验和重新铯化实验,测试了Cs/O激活后和重新补Cs后的光谱响应曲线和光电流衰减曲线.实验结果表明,在100 lx白光照射条件下,超高真空环境中的GaAlAs光电阴极在Cs/O激活后和重新补Cs激活后的光电流衰减寿命相比GaAs光电阴极更长,并且在多次补Cs激活后呈现较一致的蓝绿光响应能力和光电流衰减寿命,体现了GaAlAs光电阴极在真空系统中稳定性和可重复性使用方面具有的优越性,为海洋真空探测器件和真空电子源领域的研究提供了实验指导.     

Numerical simulation of the magnetoresistance effect controlled by electric field in p–n junction

The magnetoresistance effect of a p–n junction under an electric field which is introduced by the gate voltage at room temperature is investigated by simulation. As auxiliary models, the Lombardi CVT model and carrier generationrecombination model are introduced into a drift-diffusion transport model and carrier continuity equations. All the equations are discretized by the finite-difference method and the box integration method and then solved by Newton iteration.Taking advantage of those models and methods, an abrupt junction with uniform doping is studied systematically, and the magnetoresistance as a function of doping concentration, SiO_2 thickness and geometrical size is also investigated. The simulation results show that the magnetoresistance(MR) can be controlled substantially by the gate and is dependent on the polarity of the magnetic field.     

The influence of electronic transport across interface junction between Si substrate and the root of ZnO micro-prism on field emission performance

ZnO micro-prisms are prepared on the p-type and n-type Si substrates, separately. The $I$--$V$ curves analysed by AFM show that the interface junctions between the ZnO micro-prisms and the p-type substrate and between the ZnO micro-prisms and the n-type Si substrate exhibit p--n junction behaviour and ohmic contact behaviour, respectively. The formation of the p--n heterojunction and ohmic contact is ascribed to the intrinsic n-type conduction of ZnO material. Better field emission performance (lower onset voltage and larger emission current) is observed from an individual ZnO micro-prism grown on the n-type Si substrate. It is suggested that the n-Si/n-ZnO interfacial ohmic contact benefits the electron emission; while the p-Si/n-ZnO interface heterojunction deteriorates the electron emission.     

Enhanced absorption process in the thin active region of GaAs based p–i–n structure

The optical absorption is the most important macroscopic process to characterize the microscopic optical transition in the semiconductor materials. Recently, great enhancement has been observed in the absorption of the active region within a p–n junction. In this paper, Ga As based p–i–n samples with the active region varied from 100 nm to 3 μm were fabricated and it was observed that the external quantum efficiencies are higher than the typical results, indicating a new mechanism beyond the established theories. We proposed a theoretical model about the abnormal optical absorption process in the active region within a strong electric field, which might provide new theories for the design of the solar cells,photodetectors, and other photoelectric devices.     

描述光伏效应的新解析模型

对陆启生等人提出的描述光伏效应的解析模型涉及的边界条件进行了讨论,提出了一个适用性更宽的解析模型。通过对新模型、陆的模型以及另一个解析模型的比较,对前两个模型能够描述光伏型光电探测器在强光辐照时的信号饱和效应的原因进行了解释。