不同结构的反射式GaAs光电阴极的光谱特性比较

利用分子束外延生长了三种结构的反射式GaAs光电阴极,其中一种为传统结构的反射式GaAs光电阴极,另外两种为具有GaAlAs缓冲层的均匀掺杂和梯度掺杂反射式GaAs光电阴极.激活后的光谱响应测试结果表明,与传统结构的反射式GaAs光电阴极相比,具有GaAlAs缓冲层的均匀掺杂反射式GaAs光电阴极的长波响应更好,而具有...     

国外GaAs光电阴极光谱响应特性比较与分析

对国外标准三代、高性能三代、超三代和四代GaAs光电阴极进行了光谱响应曲线比较。结果显示，GaAs光电阴极的积分灵敏度、响应的截止波长、峰值响应和峰值位置存在明显差异。曲线拟合结果表明国外GaAs光电阴极的后界面复合速率较低，表面逸出几率和电子扩散长度从标准三代到四代不断提高，这些性能的改善导致了GaAs光电阴极灵敏度的提高。     

InP/InGaAs/InP红外光电阴极时间响应特性的模拟研究

文中理论研究了InP/In0.53Ga0.47As/InP异质结透射式红外光电阴极的时间响应特性,光谱响应范围1.0～1.7 m。在场助偏压的作用下,模拟计算了光激发的电子在阴极内部的传输特性。模拟计算表明,光电阴极的响应速度随场助偏压的增大而加快;随光吸收层厚度的增大而减慢;随光吸收层掺杂浓度的增大,光电阴极的响应速度变慢。发射层厚度及掺杂浓度的增大都会使得阴极的响应时间加长。经过对阴极结构参数和掺杂浓度的优化,得到在吸收层和发射层厚度分别为2 m、0.5 m,掺杂浓度分别为1.51015 cm-3、1.01016 cm-3时,在适当场助偏压下光电阴极的响应时间可优于100 ps。     

透射式GaAs光电阴极响应时间的理论分析

本文以光生电子处于非稳态的观点,分析了透射式GaAs光电阴极的响应时间,从理论上解释了C.C.Phillips等人的测量结果。指出透射式GaAs光电阴极是一种可用于时间响应为皮秒量级的良好光电阴极。     

指数掺杂透射式GaAs光电阴极表面光电压谱研究

通过求解一维稳态少数载流子扩散方程,推导了指数掺杂和均匀掺杂的透射式GaAs光电阴极表面光电压谱理论方程。利用金属有机化学气相沉积(MOCVD)外延生长了发射层厚度相同、掺杂结构不同的两款透射式阴极材料。通过表面光电压谱实验测试和理论拟合发现指数掺杂结构在发射层厚度和后界面复合速率相同的情况下能够有效提高阴极电子扩散长度,这主要由于内建电场能够促使光生电子通过扩散和电场漂移两种方式向表面运动,从而最终提升阴极的发射效率和表面光电压谱。利用能带计算公式和电子散射理论对这两种不同结构材料的表面光电压谱进行了详细分析。     

高温激活的变掺杂GaAs光电阴极研究

为了获得高量子效率的GaAs光电阴极,要求GaAs材料的电子扩散长度足够长,且电子表面逸出几率大,而这两个参数都要受到P型掺杂浓度的限制。经过对由体内到表面掺杂浓度由高到低的变掺杂GaAs光电阴极进行比较深入的激活实验和光谱响应理论研究,实验结果显示,适当的表面掺杂浓度GaAs光电阴极材料,在高温激活结束后获得了较高的灵敏度和较好的稳定性。根据实验结果和反射式变掺杂GaAs光电阴极量子效率理论预测曲线,对变掺杂GaAs光电阴极材料掺杂结构提出了进一步优化的思路。研究表明,变掺杂GaAs光电阴极将成为发展我国高性能GaAs光电阴极的一项重要途径。     

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.     

高量子效率InP/In0.53Ga0.47As/InP红外光电阴极模拟

将In0.53Ga0.47As吸收层设计为多个薄层,通过不同浓度掺杂实现吸收层杂质指数分布,建立了InP/In0.53Ga0.47As/InP红外光电阴极模型,在皮秒级响应时间的前提下模拟了吸收层厚度、掺杂浓度和阴极外置偏压对阴极内量子效率的影响,给出了光电子在吸收层和发射层的一维连续性方程和边界条件,计算了光电子克服激活层势垒发射到真空中的几率,进而获得阴极外量子效率随上述三个因素的变化规律,结果表明,吸收层掺杂浓度在1015~1018 cm-3范围内变化时,内量子效率变化很小;随着吸收层厚度在0.09~0.81 m内增大,内量子效率随之增大;随着外置偏压升高,内量子效率先增大后趋于平稳。文中给出一组既能获得高量子效率又能有快时间响应的阴极设计参数,理论上1.55 m入射光可以获得8.4%的外量子效率,此时响应时间为49 ps。     

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．     

高真空系统气体成分对GaAs光电阴极稳定性的影响

GaAs 光电阴极以其量子效率高、光谱可调等优点广泛应用于微光夜视领域,尤其以高积分灵敏度的特性区别于多碱光电阴极,而 GaAs 光电阴极负电子亲合势的特性是通过 Cs,O 激活实现的,但是激活结束后,负电子亲合势的维持受诸多因素影响,如激活源、激活方式、气体氛围等。为了探究超高真空系统中影响 GaAs 光电阴极稳定性的因素,开展了 GaAs 光电阴极的激活实验和稳定性实验,对激活光电流曲线与腔室气体成分进行了监测,实验结果表明,在真空度优于 1×10^-6 Pa 的高真空系统中,影响其稳定性的是腔室中的气体成分,其中对稳定性影响最大的是 H₂O,真空系统中 H₂O分压的增加会导致 GaAs 光电阴极的 Cs,O 激活层迅速破坏,光电发射能力急剧下降。     

Resolution Characteristics of GaAs/GaAlAs Transmission Photocathode

The reolution characteristic of GaAs/GaAlAs trransmission photocathode is an important parameter in third generation intensifiers.The modulation transfer function of GaAs/GaAlAs transmission photocathode is derived from a simple two-dimensional diffusion equation.The theoretical resolution characteristic of a 2 μm thick GaAs/GaAlAs transmission photocathode is calculated.The relationship between resolution and parameters in GaAs/GaAlAs transmission photocathode is discussed.A conclusion is shown that one can design the GaAs/GaAlAs transmission photocathode for maximum quantum efficiency,since the sacrifice in the resolution doesn‘t limit system performances.     

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。     

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.     

New GaAlAs-GaAs surface-emitting laser diodes with lateral pumping structure

We have fabricated a new GaAlAs/GaAs surface-emitting laser diode with lateral pumping structure. With this structure, the thickness of the active layer can be increased beyond the electron diffusion length, and also both current and light confinement can be incorporated. The lowest threshold current was 180 mA. The far-field pattern shows stable double lobes with an FWHM of 39°. By reducing the size of the mesa, making the wall of the mesa vertical and using the GaAlAs/GaAs quarter-wave stack for the mirror, further improvement can be expected.     

Emitter—Base bandgap grading effects on GaAlAs/GaAs heterojunction bipolar transistor characteristics

Emitter-base bandgap grading effects on GaAlAs/GaAs heterojunction bipolar transistor characteristics are theoretically investigated using an accurate one-dimensional numerical model including aluminum mole-fraction-dependent velocity versus field characteristics and donor energy level. The bandgap grading is shown to influence not only the electron injection but also the carrier recombination and the hole injection, resulting in a significant common-emitter current gain dependence on the graded layer thickness. The cutoff frequency dependence on the graded layer thickness is also described. Detailed discussion is given for the underlying physical mechanism that determines the device performance.     

发射层对指数掺杂Ga1-χAlχ As/GaAs光阴极性能的影响

为了探索发射层厚度对指数掺杂Ga1-χAlχAs/GaAs光电阴极光学性能与光电发射性能的影响,实验制备了两种发射层厚度不同的阴极样品,并测试得到400μm～1 000 nm内反射率、透射率与光谱响应曲线.实验结果说明发射层2.0 μm厚的样品比1.6μm厚的样品性能更好.利用薄膜光学矩阵理论公式计算阴极膜系反射率、透...     

Very high-transconductance short-channel GaAs MESFETs with Ga0.3Al0.7As buffer layer

MESFETs with 0.17?m gate length were manufactured with an n+GaAs active layer (3 × 1018cm-3) and an undoped Ga0.3Al0.7As buffer layer grown by molecular-beam epitaxy. The deives showed very high transconductance (700mS/mm) with good pinchoff characteristics. The experimental transconductance values were compared with calculated ones using a model that assumed total carrier confinement within the active layer by a barrier potential at the GaAs/GaAlAs interface. The results suggest that very high-transconductance short-gate-length MESFETs can be fabricated with a heavily doped GaAs active layer provided that the carrier density in the active layer is maintained at the doping level.     

Modeling of the frequency modulation response of semiconductordiode lasers

The modulation response of GaAlAs semiconductor diode lasers has been studied theoretically, with emphasis on wavelength modulation or frequency chirp. The laser model used is a nonlinear rate equation model that incorporates the wave equation for the lateral waveguide modes of the laser. Lateral diffusion of carriers in the active layer of the laser is taken into account via a one-dimensional diffusion equation. A small-signal analysis of the model has been performed to obtain the modulation response. The calculated amplitude and phase of the wavelength modulation relative to the power modulation are in good agreement with experiments. It is found that carrier diffusion has only a moderate influence on the modulation response     

GaAs／GaAsAl阴极粘结X射线双晶衍射测量

分析了ＧａＡｓ／ＧａＡｓＡｌ阴极粘结工艺中应力产生的根源和晶体中应力对Ｘ射线双晶衍射峰的宽度和强度的影响，用Ｘ射线双晶衍射仪测量阴极和玻璃热粘结工艺过程中的阴极材料外延层和衬底的双晶回摆曲线，实验结果表明，ＧａＡｓ／ＧａＡｓＡｌ阴极粘结工艺没有带来明显的附加应力，外延层衍射角的展宽是由于ＧａＡｓ阴极组件窗玻璃的非晶态性所致。