NEA GaN光电阴极光电发射机理研究

围绕GaN光电阴极NEA特性的成因,结合激活过程中光电流变化规律和成功激活后阴极表面模型,研究了NEA GaN光电阴极光电发射机理.实验表明:NEA GaN激活过程中光电流在约1 min之内就可达到峰值,Cs/O激活时引入O后光电流的增长幅度不大.根据Spicer光电发射理论,给出了反射模式NEA GaN光电阴极量子产额理论公式,激活成功后GaN光电阴极NEA特性的成因可以用双偶极层模型[GaN(Mg):Cs]:Cs-O解释.     

NEA GaN和GaAs光电阴极的比较

针对GaN基光电阴极激活过程中Cs-O交替存在的光电流的增幅问题,本文主要比较了GaN和GaAs材料性质、表面结构以及激活过程中光电阴极的光电流。发现GaN的熔点高于GaAs,在制备GaN基光电阴极时则需要更高的热清洗温度;如果用双偶极子模型描述GaN(1000)和GaAs(100)表面的光电发射机理,GaN(1000)表面Cs原子与O原子形成第二偶极矩O-Cs,几乎"平躺"在表面,对光电发射贡献不大;GaAs(100)表面Cs原子与O原子形成第二偶极矩O-Cs几乎"垂直"于表面,降低了表面功函数,对光电发射贡献很大;Cs-O激活过程中,对于GaAs光电阴极,Cs、O交替过程形成的光电流与单纯Cs激活时的光电流相比,有几倍甚至上百倍的增长;GaN只提高了20%左右。通过第一性原理计算,与现在的GaN基(1000)面相比,GaN基的(11 2 0)和(10 1 0)面是极具潜力的光电发射面;预计闪锌矿GaN基(100)面会取得更好的结果。     

Ⅲ-Ⅴ族半导体NEA光电阴极智能激活测试系统设计及应用研究

Ⅲ-Ⅴ族半导体负电子亲和势(NEA)光电阴极智能激活测试系统是为研究、制备NEA光电阴极材料提供的一个多信息实验数据自动采集和处理平台.它的亮点在于:在该系统上不但能完成GaAs NEA光电阴极激活,而且能进行GaN NEA.光电阴极激活的研究.其使用波长范围已从初级研究的400～1000nm延展到了200～1000n...     

透射式GaAs光电阴极时间分辨特性研究

时间分辨特性是GaAs光电阴极应用于泵浦探测等领域的一种极为重要的性能参量。采用矩阵差分求解光电子扩散模型的方式计算了光电子连续性方程和出射光电子流密度方程，发现影响GaAs光电阴极时间分辨特性的因素包括GaAs/GaAlAs后界面复合速率、GaAs电子扩散系数和GaAs激活层厚度，之后较为系统地研究了这三种物理因素对GaAs光电阴极时间分辨特性的影响。研究结果表明，GaAs电子扩散系数和GaAs/GaAlAs后界面复合速率与光电阴极的响应速率存在非线性正比关系，且随着两者的增大，GaAs光电阴极将出现饱和响应速率。激活层厚度对GaAs光电阴极响应时间的影响最大，通过激活层厚度的适当减薄可以将GaAs光电阴极的响应时间缩短至20 ps，可满足绝大多数光子、粒子探测的快响应需求。该研究为快响应GaAs光电阴极的实验和应用提供了必要的理论支撑。     

NEA光电阴极研究的最新进展及其制备技术探讨

以GaAs为代表的NEA光电阴极的应用范围越来越广,经过几十年的发展,NEA光电阴极的研究已经取得比较显著的成就,但就NEA光电阴极本身而言,尚有许多问题没研究清楚.从NEA光电阴极的掺杂方式、激活工艺、性能评估、铟封工艺和稳定性等方面探讨了最新的研究进展,给出了最新的技术指标及实现这些指标的方法,为下一步的深入研究提供必要的参考.     

GaAs光阴极激活稳定性研究

为了提高Cs-O激活后GaAs光阴极的稳定性,延长像管的使用寿命,从Cs-O激活方面着手进行研究,寻找解决途径。改变GaAs光阴极激活中的Cs过量,并在线监测真空环境下光电流的变化情况,寻找激活对GaAs光阴极稳定性的影响因素。分别进行3组5种比例的激活实验,在光电流下降至Cs峰峰值90%、70%、50%、30%和10%时给O进行交替激活。激活结束后,在低于110-8Pa的真空环境下在线监控30min内的光电流,发现过Cs90%、70%、50%激活的光阴极稳定性好,过Cs30%次之,过Cs10%相对最差。结果表明:GaAs光阴极Cs-O激活时,Cs量越多,表面势垒的建构越完整,光阴极的稳定性就越好,对改善GaAs光阴极稳定性,延长使用寿命具有重要意义。     

GaP■-1×1表面的Ga 3d化学位移

单色的 Hellα(hv=40.8eV)光电子发射测量发现:在IBA的 GaP(III)-1×1表面上,最外层Ga原子的3d能级结合能比体内减小0.75±0.05eV.解释为表面原子的极化程度低于体内.     

β-GaS钝化的GaAs表面的光电子能谱

在GaAs表面淀积β-GaS是一种可行的GaAs表面钝化方法.用光电子能谱研究了超薄GaS淀积后的GaAs表面,分析了表面成分.并发现GaS的淀积能使GaAs原有的表面能带弯曲减小0.4eV,这意味着表面费米能级钉扎在一定程度上得到消除.给出了一个半定量的理论模型,来解释GaS淀积引起的能带弯曲减小与以前湿法钝化引起的能带弯曲增大之间的不同.     

GaP(-1-1-1)-1×1表面的Ga3d化学位移

单色的 Hellα(hv=40.8eV)光电子发射测量发现:在IBA的 GaP(III)-1×1表面上,最外层Ga原子的3d能级结合能比体内减小0.75±0.05eV.解释为表面原子的极化程度低于体内.     

高温退火对GaAs光阴极表面状态的影响

利用XPS分析了GaAs光阴极高温退火、激活前后表面组分的变化,结合光阴极退火过程中通过四级质谱仪获取的CO2、H2O、O、As、Cs等分压曲线,比较、讨论了两次退火机理的差异。提出第二次加热的目的不仅在于清洁光阴极表面,更重要的是促使第一次激活在光阴极表面形成的偶极层向更稳定的结构转化,Cs2O偶极子在高温下与GaAs本底反应生成了可在光阴极表面稳定存在的GaAs-O-Cs偶极子,形成主要由键合强的GaAs（Zn）--Cs+、GaAs-O-Cs偶极子及靠范德瓦尔斯力附着在光阴极表面的Cs2O偶极子构成的偶极层。根据这一结论,解释了光阴极两次激活过程中光电流变化规律的差异。对理解光阴极激活及表面光电发射模型具有重要意义。     

GaN与GaAs NEA光电阴极稳定性的比较

利用自行研制的光电阴极激活评估实验系统,对激活后的反射式GaN及GaAs光电阴极进行了稳定性测试,获得了Cs/O激活一段时间后阴极随时间变化的光谱响应,通过计算得到量子效率曲线.结果表明:激活结束后GaN灵敏度可以在较长时间内保持稳定,而后缓慢衰减.而GaAs光电阴极的光电流随时间近似呈指数衰减.结合阴极表面双偶极层结构以及表面化学成分,分析原因主要是:两种阴极表面进行Cs/O激活后形成的双偶极子的结构不同、衰减过程中双偶极层化学成分变化方式不同决定.GaN光电阴极激活后cs以复杂氧化物存在,更加稳定,灵敏度的衰减主要是由未分解的氧引起,而GaAs灵敏度下降的原因主要是表面双偶极层中的Cs极易脱附,影响其稳定性.     

The application of semiconductors with negative electron affinity surfaces to electron emission devices

Semiconductors with negative electron affinity (NEA) surfaces are used as photoemitters, secondary emitters, and cold-cathode emitters. A comprehensive review of the characteristics and applications of these materials is presented, the concept of NEA is described, and a comparison is made between NEA and conventional emitters. Electron generation, transport, and emission processes of NEA emitters are discussed. NEA III-V compound photocathodes, especially GaAs, are described with respect to their fabrication, performance, and applications to photomultipliers and image intensifier tubes. The structure and performance of NEA secondary emitters are presented. NEA GaP secondary-emission dynodes represent the most important device application. NEA cold cathodes, using GaAs, Ga(As, P), or Si, have been investigated, and their performance characteristics are summarized. NEA Si cold cathodes have been incorporated in developmental TV camera tubes. The characteristics of these tubes are reviewed.     

Selective emission of electrons from patterned negative electronaffinity cathodes

We have observed electron emission into vacuum from the exposed areas of a patterned p⁺⁺-GaAs substrate which was coated with cesium and oxygen. The emission barrier is a double layer of titanium-tungsten/silicon nitride. The exposed areas of the cathode were activated to the negative electron affinity (NEA) condition. It has been an open question whether it would be possible to activate the exposed areas of a patterned GaAs cathode. This result opens the possibility of utilizing NEA cathode technology for projection electron beam lithography tools, NEA-based vacuum microelectronics devices, and a combination of bulk devices with NEA emitters. A picture of an emission pattern projected onto a phosphor screen is presented. Auger depth profile was used to determine the stability of the TiW/GaAs interface through the activation procedure. Short and long term current stability were measured. A technique for cathode recovery and reactivation has been developed     

Low-threshold 833-nm GaAsP-AlGaAs tensile-strained quantum-well laser diodes

We report the demonstration of TM polarized laser emission at 833 nm from GaAsP-AlGaAs quantum well laser structures grown on GaAs substrates by low-pressure organometallic vapor phase epitaxy for the first time. This is the longest wavelength near infrared TM polarized laser ever reported. Broad area laser diodes containing single GaAs/sub 0.95/P/sub 0.05/ quantum well lased at a low threshold current density of 280 A/cm/sup 2/ for a cavity length of 1 mm and with a high differential quantum efficiency of 32%/facet for cavity length less than 500 /spl mu/m.     

In segregation effects during quantum dot and quantum ring formation on GaAs(001)

In segregation during InAs growth on GaAs(001) is studied using a real time, in situ technique capable of measuring sample accumulated stress. A 50% surface In segregation of liquid-like stress free matter is deduced. A picture of growth below critical thickness for quantum dot formation is discussed on the basis of the equilibrium between pseudomorphic InAs and liquid In dominated by the stress energy. Quantum rings are produced when large (>10 nm height) quantum dots are covered with 2 nm of GaAs cap. A formation mechanism of the rings is presented. The possibility of tailoring photoluminescence emission through control over size and shape is demonstrated.     

Mean Transverse Energy of Electrons Emitted from GaAs/GaAlAs Transmission Photocathode

A GaAs/GaAlAs transmission photocathode surface topography is examined with a scanning electron microscope(SEM)in the secondary emission mode.The contributions of photocathode surface topography to mean transverse energy of electrons emitted from the photocathode are calculated.Measurement is made of the variation of mean transverse emission energy with activating time during the course of activation.It is shown that the scattering of the photoelectrons in the Cs/O layer is the primary cause of the unexpectant high values of the mean transverse energy of electrons emitted from GaAs/GaAlAs photocathod.A method is proposed for the reduction of te mean transverse energy of electrons emitted from the photocathode.     

GaAs/GaAlAs透射式光电阴极发射电子的平均横向能量

用扫描电镜观测了 Ｇａ Ａｓ／ Ｇａ Ａｌ Ａｓ 透射式光电阴极的表面形貌,计算了阴极表面形貌对阴极发射电子的平均横向能量的贡献,测量了阴极激活过程中阴极发射电子的平均横向能量随激活时间的变化。结果表明, Ｇａ Ａｓ／ Ｇａ Ａｌ Ａｓ 阴极表层的 Ｃｓ／ Ｏ 激活层对电子的散射是导致阴极发射电子的平均横向能量值增高的根本原因。最后提出减少阴极发射电子的平均横向能量的技术途径。     

Anomalous polarization of Raman scattering by transverse and longitudinal phonons in porous doped GaAs

The Raman spectra of a porous doped GaAs(100) crystal were studied. It is established that emission in the plasma-phonon spectra of both the starting and porous crystals is highly polarized and is independent of the incident-radiation polarization. It is inferred that the contribution of the Froelich mechanism to the intensity of the plasma-phonon spectrum is predominant and that the effects of defects and multiple scattering on the scattered-light polarization in porous GaAs may be ignored. The cause for the violation of the selection rules in the spectrum of porous crystal is discussed.     

NEA光电阴极的表面模型

回顾了NEA光电阴极不同的表面模型，对异质结模型、偶极子模型和铯的弱核力效应进行了重点介绍。异质结模可以成功解释P型GaAs和（Cs,O）激活层之间界面势垒的存在，但这种具有体效应的异质结无法与（Cs，O）层的厚度相统一；偶极子模型认为在阴极表面形成的偶极层导致了逸出功的下降，其双偶极层模型能较好地预测和解释最佳的（Cs，O）激活层厚度，但不同的双偶极层模型对于氧在表面层存在的化学形态存在争议；铯的弱核力场效应认为铯表面层的弱核力场及氧的离化作用是界面势垒和负电子亲和势的形成原因，但它所认为的逸出功降低与基底材料无关还需进一步验证。