表面势垒形状对NEA光阴极电子能量分布的影响

通过计算电子到达阴极面时的能量分布和求解电子隧穿表面势垒的薛定谔方程得到了透射式NEA GaAs光阴极发射电子能量分布的计算公式.利用该公式仿真研究了阴极表面势垒形状对电子能量分布的影响,发现I势垒变化对阴极的量子效率影响显著,其中尤以I势垒宽度影响更大,而Ⅱ势垒则影响阴极的能量展宽,其中真空能级的升高可使阴极电子能量分布更集中,但却牺牲了一定的阴极量子效率.拟合分析了实验测试的透射式阴极电子能量分布曲线,实验与理论曲线吻合得很好,并得到了阴极的表面势垒参数.     

Cs、O激活对GaAsP光阴极光谱响应特性的影响

为了探究Cs、O激活电流对透射式GaAsP光阴极光谱响应特性的影响,通过光谱响应测试仪测试不同Cs、O电流激活后的透射式GaAsP光阴极光谱响应曲线,结果表明,随着铯氧蒸发电流比的减小,GaAsP光阴极光谱曲线的形状会发生一定的改变,长波响应能力逐渐降低、短波响应能力逐渐提高。利用双偶极层模型理论,分析认为铯氧蒸发电流比的改变影响了GaAsP光阴极表面势垒的形状,使得不同激发能量的光电子通过隧道效应穿越表面势垒宽度发生变化,从而影响GaAsP光阴极光谱响应特性。根据此现象对进一步提高GaAsP光阴极在530 nm特征波长的量子效率具有积极的意义。     

用于探测能量为0.110keV光子的夹心结构CsI光阴极

为了稳定而有效地探测能量范围在0.110keV之间的软X射线,研制并优化了一种高低密度夹心结构的透射式CsI光阴极。它的光子探测效串大约是高密度透射式CsI光阴极的110倍。所测得的光电发射次级电子能量分布曲线与高密度CsI光阴极类似,半极限值的全宽度(FWHM)不到2eV。由于它的量子效率高而次级电子能量分布范围相当窄,这种夹心结构透射式CsI光阴极广泛地应用于软X射线探测器和计数器,特别是软X射线条纹摄相管。     

非均匀高掺杂对透射式光电阴极光电发射性能影响研究

研究分析了高掺杂浓度下幂函数掺杂阴极发射层内部形成恒定电场情况,探讨了光电阴极发射层材料内部形成恒定电场对提高透射式光电阴极量子效率中有效电子输运长度、表面电子逸出几率等参量的影响。结合掺杂浓度不同带来的光电子散射问题,对比讨论了传统的均匀掺杂、指数掺杂、幂函数掺杂情况下发射层材料量子效率情况。     

梯度掺杂GaN光电阴极的光谱响应测试与分析

用光谱响应测试仪得到了反射式梯度掺杂GaN光电阴极在激活和衰减过程中的光谱响应曲线,发现此曲线不断发生变化。在激活过程中光谱响应不断提高,且长波响应提高较快;衰减过程中光谱响应不断下降,长波响应下降得更快。结果表明：光谱响应曲线的变化与光电阴极高能光电子的逸出有关。GaN光电阴极发射的电子能量分布随入射光子能量升高而向高能端偏移,阴极表面势垒形状的变化对低能光激发电子的影响更大,导致光谱响应曲线随入射光波长改变而产生了不同的变化。     

NEA GaN光电阴极材料光学特性研究

针对NEA GaN光电阴极结构设计和制备工艺需进一步优化的问题,结合阴极量子效率表达式和影响量子效率的因素,采用理论和实验相结合的方法,分别研究了GaN光电阴极材料的表面反射率、光学折射率、光谱吸收系数以及透射光谱等光学参数。结果表明在250 nm到365 nm的波长范围内,表面反射率相对平稳,是影响量子效率的直接因素,而光学折射率则通过电子表面逸出几率间接影响着量子效率。给出了均匀掺杂GaN光电阴极的光谱吸收系数的特点,根据变掺杂NEA GaN光电阴极的结构特点,给出了光谱平均吸收系数的概念和等价计算公式,并对均匀掺杂与变掺杂NEA GaN光电阴极光谱吸收系数进行了对比。     

转移电子光电阴极电子传输特性的蒙特卡罗模拟

本文利用蒙特卡罗模拟方法计算了转移电子光电阴极的光电子输运特性，其中包括阴极的内部量子效率，电子的能量分布函数，谷间转移效率，同时也给出了阴极的时间响应特性．     

多碱光电阴极光电发射过程研究

论述了多碱阴极及光致荧光的特点,测量了多碱阴极在514.5 nm和785 nm波长激光激发条件下的荧光谱。结果表明,多碱阴极在514.5 nm波长激光激发条件下,荧光峰值强度比785 nm波长激光激发条件下荧光峰值强度强40倍,说明514.5nm波长的电子跃迁几率低于785nm波长的电子跃迁几率,同时514.5 nm波长激光激发的荧光峰值波长为860 nm,而785 nm波长激光激发的荧光峰值波长为870 nm,514.5 nm波长激光激发的荧光峰值波长与激发光波长的偏移为345 nm,而785 nm波长激光激发的荧光峰值波长与激发光波长的偏移仅为85 nm,说明514.5 nm波长激发的跃迁电子的能量损失远大于785nm波长激发的跃迁电子的能量损失。原因是短波光子的能量较高,所激发的跃迁电子来源于较深能级,因此能量损失较大。多碱阴极的量子效率在2.11 eV达到最大,当光子的能量大于2.11 eV以后,由于跃迁电子的能量损失随光子能量的增加而增加,因此多碱阴极的量子效率随光子能量的增加而减小。多碱阴极的量子效率与电子跃迁几率成正比,但实测的量子效率曲线与电子跃迁几率曲线的峰值波长不一致,原因是随着光子能量的增加,跃迁电子的能级也增加,当电子跃迁的几率达到最大并下降时,尽管跃迁电子的几率减小,但因电子跃迁的能级还在提高,因此量子效率仍在增加。只有当跃迁几率的因素超过能级的因素以后,量子效率才随光子能量的增加而减小,因此造成量子效率曲线的峰值波长与跃迁几率的峰值波长不一致。通过多碱阴极光致荧光谱的分析,揭示了多碱阴极电子跃迁过程中的客观规律,解释了多碱阴极量子效率在达到最大值之后,量子效率随光子能量增加而减小以及多碱阴极量子效率存在短波限的原因。     

K_2SbCs光电阴极光谱响应特性模拟

为了探索高性能K_2SbCs光电阴极的特征结构,对光电阴极量子效率公式进行了推导,并利用推导出的公式对K_2SbCs光电阴极量子效率(≈30%)曲线进行拟合,得到拟合相对误差较小结构参数。另外,根据拟合结果分析了对光谱响应造成影响的因素,包括阴极厚度、光电逸出深度、阴极结构参量、光谱响应截止波长等。探索了该光电阴极结构参数范围,据此分析并设计高性能透射式K_2CsSb光电阴极。     

均匀掺杂GaAs光阴极表面势垒特性研究

根据激活过程中光电流变化规律及原位光谱响应测试,模拟了GaAs光阴极表面势垒的形成过程,在光阴极表面双偶极子模型的基础上作了修正,建立了三偶极子模型。新模型认为,光阴极表面势垒由三个偶极层套构而成,第一偶极层由GaAs（Zn）-Cs+偶极子组成,第二偶极层由Cs2O偶极子组成,第三偶极层由GaAs-O-Cs偶极子组成,第二、三偶极层嵌入第一偶极层中。根据隧道效应与量子效率测试结果,确立了势垒中分段均匀的电势分布,计算得出势垒宽度为1.65 nm,有效电子亲和势为-0.44 eV。新模型的建立对理解光电阴极表面发射机理具有重要意义。     

Photoemission characteristics of transmission-mode negative electron affinity GaAs and (ln,Ga)As vapor-grown structures

Several types of transmission-mode negative electron affinity (NEA) photocathodes were investigated. The first group consisted of GaAs cathodes of various thicknesses grown on a composite structure composed of a GaP substrate and a Ga(As,P) buffer layer. These cathodes were of two types, one having an abrupt Ga(As,P)/GaAs interface and the other having a compositionally graded interface. The latter type exhibited the highest transmission-mode quantum efficiency, 0.11 electron per incident photon at 0.85 μm. It is assumed that the electron diffusion length L in the GaAs layer is limited by misfit dislocations arising from the lattice mismatch between the GaAs and the Ga(As,P) buffer layer. L increased with cathode layer thickness more rapidly for the graded structure, suggesting that misfit dislocation propagation into the GaAs layer is less when the dislocations are generated gradually (graded structure) than when they are introduced abruptly (ungraded structure). The second group of samples consisted of (In, Ga)As alloy cathodes of various compositions grown on both GaAs and GaP substrates with lattice-mismatch-reducing buffer layers of (In, Ga)As, (In, Ga)P, and Ga(As,P). It was found that photosensitivity was improved significantly by reducing the amount of lattice mismatch between the (In, Ga)As cathode layer and the substrate or buffer layer. Using an (In, Ga)As cathode with an (In,Ga)P buffer layer grown on a GaP substrate, transmission quantum efficiencies in excess of 0.01 were obtained over the relatively broad wavelength range of 0.7 to 1.04 µm.     

纳米量子点能级以及能隙计算和修正

用一个简单模型分析了量子点产生能级的原因,推导出能级与量子点尺寸的表达式。根据量子点表面势垒为有限值的特点以及表面存在衰减波,提出量子点内电子波函数不完全满足驻波条件的观点,在量子点的能级表达式中引入一个修正系数。结合量子点表面衰减波的特征,给出量子点修正系数的计算方法。通过理论计算表明：量子点的能级以及能级之间的能量差（间隙）不但与量子点的尺寸有关,而且与其边界条件有关。特别是对于非光滑的表面,其表面势垒对量子点的能级与能隙影响非常大。     

A high performance inverted organic light emitting diode using an electron transporting material with low energy barrier for electron injection

A high performance inverted green emission organic light emitting diode with a maximum external quantum efficiency of 20% and a maximum power efficiency of 80 lm/W was realized by properly selecting an electron transporting material to have no energy barrier for electron injection between the n-doped electron transporting layer (n-ETL) and the ETL. Based on the energy levels and the current density–voltage characteristics of electron only devices, we demonstrate that the interface between an n-ETL and an ETL even in homo-junction is as important as the interface between the cathode and the n-ETL for efficient electron injection into an emitting layer.     

用异质结构控制GaN阴极电子发射

从自洽求解薛定谔方程和泊松方程出发,研究了GaN异质结构上偏压变化时异质结电场的变化。发现异质结量子阱能把外电场屏蔽在异质界面以外。利用这种异质结量子阱的屏蔽效应,可以使外电场都降落在异质结表面来控制表面势。为了把表面电势剪裁成半导体阴极所需的陡直下降的电势结构,进一步深入研究了双势垒异质结的电场结构,发现外面的异质结能屏蔽里面异质结的势垒。利用这种双势垒异质结的屏蔽效应设计出可由偏压直接控制电子亲合势的异质结构,从而为半导体阴极开辟出一条新的研究途径。     

End-Group Functionalization of Non-Fullerene Acceptors for High External Quantum Efficiency over 150 000% in Photomultiplication Type Organic Photodetectors

Photomultiplication-type organic photodetectors (PM-OPDs) with high external quantum efficiency (EQE) of over 100% are attracting increasing attention due to their potential importance in detecting weak incident light. Considering that the gain of PM-OPD is determined by the ratio of carrier lifetime over carrier transit time, a systematic study on the effect of the end-functionalization of a new extended aromatic fused-ring non-fullerene acceptor (NFA) on the carrier trap/transit time of the PM-OPD. Photophysical analyses by means of ultraviolet-visible absorption, ultraviolet photoelectron spectroscopy, and photoluminescence combined with structural analyses through grazing-incidence wide-angle X-ray scattering show that fluorination of the NFA with the deepest lowest unoccupied molecular orbital level and non-isotropic molecular ordering can yield the longest carrier lifetime. Furthermore, surface energy study show that fluorination of the NFA can also yield the most hydrophobic nature, which can allow the most efficient injection barrier thinning/lowering of the active layer/cathode interface under illumination due to the localized acceptor distribution toward cathode, maximizing the hole injection efficiency from cathode. As a result, an unprecedentedly high EQE of 156 000% is obtained from the optimized PM-OPD. This work shows the importance of the molecular design of acceptor molecules in fabricating high-performance PM-OPDs.     

Microstructure analysis in strained-InGaN/GaN multiple quantum wells

The barrier thickness effect on the energy and microstructure properties of InGaN/GaN multiple quantum wells is investigated with Stillinger-Weber potential. The calculation indicates that the energy of a quantum well increases as the GaN barrier thickness rises, and that Ga-N and In-N bonds are shrunk with respect to those of random InGaN alloy. Moreover, a critical value of the barrier thickness exits. If the barrier thickness exceeds the critical value, the bond length of Ga-N in quantum wells reduces as a function of indium concentration. This singular behavior of Ga-N bond is analyzed with a force balance model.     

平面平行真空微电子二极管中二分之三次方关系式的应用

在一定的假定条件下，考虑空间电荷影响，平面平行真空微电子（P—VMD）二极管中电流一电压近似按二分之三次方关系式工作。本文在此关系式及Forler—Nordheim场发射方程的基础上，通过解简化立方方程，进一步推导出管内的电位、电场强度、电子速度和空间电荷密度的分布函数。P-VMD二极管在保持管内结构与阴极表面电场强度不变，并工作在典型工作状态（归一化电位系数P=2／3）情况下，考虑空间电荷影响时的阳极电压、阳极电场强度和阳极电子速度分别比无空间电荷影响时增加约50．00％，73．21％和22．47％。P—VMD二极管内的空间电荷密度分布函数为正割函数，在阳极表面附近为最小，在阴极表面处为无穷大，这是由于本文假设在阴极表面处的电子初速度为零的缘故。