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.     

Evolution of Photocurrent during Coadsorption of Cs and O on GaAs （100）

The photocurrent and spectral response characteristics of gallium arsenide （GaAs） are obtained by a multiinformation measurement system, and the evolution of the photocurrent versus the Cs：O flux ratio is investigated. The experimental results show that the photocurrent increases approximately exponentially after the first exposure to Cs until a maximum sensitivity is reached, the detailed evolution process and the ultimate photocurrent are different for different samples. These differences are analysed, and according to the process of coadsorption of Cs and oxygen on GaAs, an equation is presented to explain the increase of photocurrent.     

Improving the performance of a GaAs nanowire photodetector using surface plasmon polaritons

GaAs nanowires (NWs) are ideal materials for preparing near-infrared photodetectors owing to their high charge carrier mobility and direct band gap. Although the performance of GaAs NW photodetectors can be enhanced by surface passivation or doping, it still cannot meet the requirement for applications. In this paper we propose a method to greatly improve the performances of GaAs NW photodetectors by hot-hole injection via surface plasmon polaritons. In this case, the responsivity of a single GaAs NW photodetector is increased by a fact of 3.2 to 6.56 A· W^-1 by attaching capsule-like Au nanoparticles to its surface. This research uses an efficient route to improve the NW photocurrent, which is also important for the development of a high-performance near-infrared NW photodetecor.     

Photoemission from p-GaAs(001) with nonequilibrium cesium overlayers

The dependences of the photoemission current and effective electron affinity on the submonolayer cesium coverage at the adsorption of Cs on a GaAs(001) surface, as well as the kinetics of the photocurrent and affinity after the termination of Cs deposition, which is caused by the relaxation of the structure of a nonequilibrium adsorption layer, have been experimentally studied. The revealed features in the dependence of the photocurrent on the Cs coverage are attributed to a nonmonotonic behavior of the surface band bending in the Cs/GaAs(001) system. It has been established that a relaxation decrease in the photocurrent in the case of coverages smaller than half a monolayer is due to the relaxation of the band bending, whereas an increase in the photocurrent at larger coverages is caused by the relaxation of the electron affinity.     

Photocurrent response in a double barrier structure with quantum dots–quantum well inserted in central well

We report the photocurrent response in a double barrier structure with quantum dots–quantum well inserted in central well. When this quantum dots–quantum well hybrid heterostructure is biased beyond +1 or −1 V, the photocurrent response manifests itself as a step-like enhancement, increasing linearly with the light intensity. Most probably, at proper bias condition, the pulling down of the X minimum of GaAs at the outgoing interface of the emitter barrier by the photovoltaic effect in GaAs QW will initiate the Γ–X–X tunneling at much lower bias as compared with that in the dark. That gives rise to the observed photocurrent response.     

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.     

1.55 μm低温生长GaAs谐振腔增强型探测器

利用低温（200℃）生长的GaAs材料作为吸收层制备了GaAs基1.55 μm谐振腔增强型（RCE） 光电探测器,对其光电特性进行了分析、研究.无光照0偏压下探测器暗电流为8.0×10－12A;光电流谱峰值波长1563 nm;响应谱线半宽4 nm, 具有良好的波长选择性.     

外电路参数对GaAs光导开关导通过程的影响

通过研究不同外电路参数条件下半绝缘GaAs光导开关的输出电流波形的差异,分析了外电路电参数对GaAs光导开关导通过程和工作模式的影响。实验开关由600μm厚的半绝缘GaAs晶片制成,电极间隙为12 mm。使用波长为1 064 nm,5.2 mJ的激光脉冲进行了开关的触发实验。使用皮尔森电流探头测量开关放电电流波形。实验发现储能电容、回路电感等外电路参数对开关放电电流波形存在决定性影响,回路电感影响了导通电流的上升前沿,储能电容对于开关非线性模式的维持起决定作用,储能电容较大时才能够提供非线性模式维持所需的偏置电场。     

超晶格结构中电子的波动性

在温度T=77K,测量了GaAs/AlGaAs超晶格的光电流,观测到在ν=1589cm^-1有一个强电流峰,而在ν=1779,2129和2401cm^-1附近存在弱电流峰.分析认为,这些电流峰与电子的波动性有关.据电子波动理论计算出的光电流峰位置与实验测量结果相当一致 关键词： 超晶格 电子 波动性     

GaAs光电阴极激活后的表面势垒评估研究

根据阴极制备过程中单独Cs激活和Cs-O交替激活两个阶段产生的光电流的峰值比,结合对电子穿过表面单势垒和双势垒后能量分布的理论曲线,提出了一种评估NEA GaAs光阴极表面势垒参数的新方法.利用该方法研究的结果完全符合双偶极层模型理论,并且和对实测阴极电子能量分布曲线拟合的结果非常一致.该方法简单、有效,在不增加测试手段的前提下,丰富了对NEA GaAs光电阴极激活效果及表面特征评价的方法和途径. 关键词： GaAs 光电阴极 表面势垒 能量分布     

双束质子辐照砷化镓光电导探测器的I-V特性

 对用能量为7.5MeV和20MeV,注量为10¹¹～10¹³cm^-2的质子辐照后的砷化镓材料制作的光电导探测器的光电流和暗电流进行了测试，并由此推得电导率的变化。结果表明，经过能量为7.5MeV的质子改性后的砷化镓探测器相对于未改性的附加光电导率Δσ减少，而且随着辐照注量的增加而越小，而对于先用能量为20MeV质子辐照后再用能量为7.5MeV的质子辐照的砷化镓材料制作的探测器，其附加光电导率Δσ的减少则更为明显。对上述现象进行了分析，并根据其相应关系预测了该种探测器的响应时间、灵敏度、拖尾现象及受X射线激发的输出脉冲的后延的变化情况。     

GaAs光电阴极激活时Cs的吸附效率研究

从NEA GaAs光电阴极的激活光电流曲线发现,当系统真空度不很高时,在首次Cs激活阶段,表面掺杂浓度较低的阴极材料,其光电流产生需要的时间也较长.同时,随着系统真空度的提高,这种时间上的差异又变得不再明显.该现象表明,Cs原子在阴极表面的吸附效率同表面层掺杂浓度以及系统真空度之间有直接的联系.为定量分析这种关系,本文根据实验数据建立了Cs在阴极表面吸附效率的数学模型,利用该模型仿真的结果同实验现象非常符合.该研究对进一步开展变掺杂阴极结构设计和制备工艺研究具有重要的价值和意义. 关键词： GaAs光电阴极 吸附效率 真空度 表面掺杂浓度     

Determination of diffusion length of minority carriers in epitaxial layers by photocurrent spectroscopy

We have determined the minority carrier diffusion length in n-type and p-type GaAs epitaxial layers grown on GaAs substrates as well as on intentionally misoriented Si substrates by photocurrent spectroscopy. It is found that for heteroepitaxial GaAs-on-Si, the minority carrier diffusion length is limited by the amount of dislocation density irrespective of the doping level. The value of dislocation density obtained from diffusion length measurements agrees well with that obtained from the double-crystal x-ray diffraction measurements.     

Low-frequency noise properties of p-type GaAs/AlGaAs heterojunction detectors

We have measured and analyzed, at different temperatures and bias voltages, the dark noise spectra of GaAs/AlGaAs heterojunction infrared photodetectors, where a highly doped GaAs emitter is sandwiched between two AlGaAs barriers. The noise and gain mechanisms associated with the carrier transport are investigated, and it is shown that a lower noise spectral density is observed for a device with a flat barrier, and thicker emitter. Despite the lower noise power spectral density of flat barrier device, comparison of the dark and photocurrent noise gain between flat and graded barrier samples confirmed that the escape probability of carriers (or detectivity) is enhanced by grading the barrier. The grading suppresses recombination owing to the higher momentum of carriers in the barrier. Optimizing the emitter thickness of the graded barrier to enhance the absorption efficiency, and increase the escape probability and lower the dark current, enhances the specific detectivity of devices.     

Quantum interference control of photocurrent injection in Er-doped GaAs

We measure two-color quantum interference control of photocurrent injection in erbium-doped GaAs. The signal size is the same order of magnitude as from a low-temperature grown GaAs sample, and much larger than in a semi-insulating GaAs sample. Thus erbium-doped GaAs could be useful for fabrication of monolithic optical carrier-envelope phase detectors. We also describe a prism-based two-color interferometer useful for minimizing stray light in quantum interference control measurements.     

Adsorption kinetics of the Cs–O activation layer on GaAs(1 0 0)

In this work, we study the adsorption of (molecular) oxygen on Cs-covered GaAs(1 0 0) surfaces at RT. The study took place in a multi-method UHV system using the techniques such as low energy electron diffraction (LEED), Auger electron spectroscopy (AES), work function measurements (WF), thermal desorption spectroscopy (TDS), secondary ion mass spectroscopy (SIMS) and electron stimulated desorption (ESD) spectroscopy in correlation with the photocurrent measurements. It is shown that the oxygen burrows under the Cs overlayer and interacts at low exposures with the GaAs substrate, whereas at higher exposures oxygen interacts also with Cs leading to Cs oxides. The maximum photocurrent appears after the WF minimum and before the oxidation of Cs. Our results support the dipolar model for the explanation of the negative electron affinity effect.     

LT-GaAs飞秒光电导之电场响应特性

利用飞秒光电导自相关技术研究了LT GaAs飞秒光电导开关时间随外加偏置电场的变化规律 .实验结果显示当外加偏置电场从0.5×10⁴ V/cm 上升到9.5×10⁴ V/cm 时，光电导 开关时间开始在200fs附近缓慢变化再迅速增加到750fs.这是由于随着外加电场增加，Fren kel-Poole效应导致的EL2缺陷中心库仑吸引势垒降低和电场增强的碰撞电离效应显著增强 ，导致载流子俘获截面减小，载流子寿命增加之故. 关键词： 光电导自相关技术 载流子俘获时间 Frenkel-Poole效应 电子碰撞电离效应     

具有全方位光管理能力的光阱结构

本文提出了一种基于砷化镓(GaAs)材料且具有全方位光管理能力的纳米方形光阱结构.通过光学模拟可知,该结构在较大结构参数范围内具有优异的全向光管理能力.当该结构的有效厚度为407 nm时,在AM1.5G光照下,其光电流密度可达29.51 mA/cm~2,而在同样条件下,2000 nm厚的平面GaAs结构只能产生19.80 mA/cm~2的光电流密度.由光电模拟可知,为了获得合理的高光电转换效率,应使少数载流子寿命大于等于1.0×10~(-7 )s,表面复合速率小于等于100 s/cm.     

Crosstalk suppressing design of GaAs microlenses integrated on HgCdTe infrared focal plane array

In this study, crosstalk suppressing design of dielectric GaAs microlenses integrated on a traditional HgCdTe infrared focal plane array is presented, by exploiting the finite difference time domain technique. Responsive photocurrent of the objective pixel and crosstalk between adjacent detectors have been numerically simulated, using commercial TCAD software Apsys, for a mid-wavelength planar array with a pitch of 20 $\upmu $ m. By properly adjusting both the microlens radius and the absorber thickness, crosstalk can be notably suppressed to less than 1 % while the photoresponse is maintained or even enhanced.     

Electric field effect in the spin dynamics of self-assembled InAs/GaAs quantum dots

We identify fundamental mechanisms of electron and hole dynamics in self-organized InAs/GaAs quantum dots (QDs) subject to vertical electric fields by photocurrent investigations. We propose a spin–flip mechanism involving a spin exchange between neighboring QDs. The spin–flip process is revealed in the photocurrent dynamics when the exciton population increases unexpectedly with reverse bias.