未掺杂半绝缘GaAs中受主及电中性EL2分布的研究

测量了未掺杂半绝缘（ＳＩ）ＬＥＣＧａＡｓ中总的、电中性的ＥＬ２及净受主浓度分布和碳分布。结果表明，总ＥＬ２浓度径向分布呈Ｗ形而不是均匀的，净受主浓度径向分布呈∧形或∩形而不是Ｍ形。电中性ＥＬ２的Ｗ形径向分布由总ＥＬ２浓度的Ｗ形径向分布决定，而不是由于净受主的不均匀分布。有些样品中净受主浓度远大于碳浓度．意味着这些样品中除碳外还存在高浓度的其它受主。     

掺杂和未掺杂LEC GaAs中EL2和位错密度分布

测量比较了掺Si和未掺杂LEC GaAs晶锭不同部位EL2浓度和位错密度分布。结果表明,掺Si样品中EL2浓度径向分布和位错密度径向分布分别为M形和W形,而未掺杂样品中两者均为W形。讨论了两者间不同对应关系的机理。     

组分和热历程对LEC GaAs中深施主能级(EL2)的影响

用红外吸收的方法测量了不同组分的原生未掺杂LEC GaAs晶锭不同部位EL2浓度([EL2]),并用热处理后快速冷却的方法模拟晶体生长后冷却过程中的不同阶段,测量分析了各阶段[EL2]的变化.在实验结果的基础上对EL2生成过程及影响其生成的因素进行了讨论.     

Investigations on Au,Ag, and Al schottky diodes on liquid encapsulated czochralski grown n-GaAs〈100〉

The Schottky barrier heights of metals Au, Ag, and Al fabricated by vacuum vapor deposition on liquid encapsulated Czochralski (LEC) grown undoped ntype GaAs (n = 2.35 × 10¹⁵ cm⁻³) were measured with current-voltage (I-V) and capacitance-voltage (C-V) techniques. Good ohmic contacts were obtained through an after deposition anneal at 430°C for two minutes in an argon gas atmosphere. In the as-deposited state, Au, Ag, and Al gave very similar I-V characteristics for n-type substrates with the barrier height qϕ_b = 0.81-1.16 eV and ideality factor n = 1.02-1.15. The C-V measurement also gives the same value of barrier height. The distribution of carrier concentration along the radial distance of the wafer is of‘M’ shape. The Al/GaAs interfaces give the nonideal rectification behavior. The Au/GaAs interfaces give the near ideal rectification behavior. The barrier height of this interface is 0.89-0.92 eV and the ideality factor is about 1.10–1.19. Electron traps in the wafer have been found by constant capacitance deep level transient spectroscopy (CC-DLTS). Mainly the EL2, EL6, and EL3 (EI1) trap levels are prominent.     

GaAs中某些缺陷间的相互关系

本文根据文献中报导的数据,求出某些缺陷间的相互关系,从而对有关缺陷的构型提出些看法。所涉及的材料包括n-VPE,n-LPE,n-LEC及SI LEC GaAs,而以后者为主。     

非有意掺杂LEC SI GaAs中EL2分布特性的研究

测量比较了不同条件下热处理后非有意掺杂半绝缘(SI)LEC GaAs中EL2浓度及其分布的变化,为了分析这一变化,还检测了位错和As沉淀的分布。在实验结果基础上,对EL2分布不均匀性的起源和热处理改善EL2分布均匀性的机理进行了讨论。     

非掺杂半绝缘LECGaAs中电参数与碳浓度及EL2浓度的关系

利用范德堡方法和光吸收方法研究了非掺杂半绝缘（ＳＩ）ＬＥＣＧａＡｓ 中电参数与碳（Ｃ）浓度及ＥＬ２ 浓度的关系。通过比较实验结果和理论计算结果发现，这种半绝缘晶体中除Ｃ外还存在其它受主在电补偿中起重要作用     

热处理中As压对半绝缘GaAs缺陷的影响

在 95 0°C和 1 1 2 0°C温度下 ,对非掺杂半绝缘 LECGa As进行了不同 As气压条件下的热处理 ,热处理的时间为 2～ 1 4小时。发现不同 As压条件下的热处理可以改变 Ga As晶片的化学配比 ,并导致本征缺陷和电参数的相应变化。在 95 0°C和低 As气压条件下进行 1 4小时热处理 ,可在样品体内 (表面 1 5 0 μm以下 )引入一种本征受主缺陷 ,使电阻率较热处理前增加约 5 0 % ,霍尔迁移率下降 70 %。这种本征受主缺陷的产生是由于热处理过程中样品内发生了 As间隙原子的外扩散。提高热处理过程中的 As气压可以抑制这种本征受主缺陷的产生。真空条件下在 1 1 2 0°C热处理 2～ 8小时并快速冷却后 ,样品中的主要施主缺陷 EL2浓度约下降一个数量级 ,提高热处理过程中的 As气压可以抑制 EL2浓度下降。这种抑制作用是由于在高温、高 As气压条件下 ,发生了间隙原子向样品内部的扩散     

Inhomogeneity of the deep center el2 in GaAs observed by direct infra-red imaging

The distribution of the dominant deep trap EL2 in 7.5cm diameter crystals of semi-insulating GaAs is studied by whole slice infrared imaging. Very significant fluctuations in the neutral EL2 concentration ([EL2]ℴ) are observed, corresponding at most to variations in [EL2]ℴ of up to 80%. The different sorts of fine structure, namely cell structure and bands of high infrared absorption ("sheets" and “streamers”) lying in (110) planes running down the <001> growth directions, are described.     

2-D simulation of kink-related sidegating effects in GaAs MESFETs

Sidegating (backgating) effects in a planar structure with sidegate on the same side as MESFET are studied by two-dimensional simulation and the results are compared with those for a structure with a backgate on the back side of the substrate. The kink-related sidegating is reproduced in the planar structure, too. Its mechanism is discussed and is attributed to the change of EL2's role from an electron trap to a recombination center by capturing holes, which are generated by impact ionization and flow into the semi-insulating substrate including EL2 (deep donor). The dependence of shallow acceptor density in the semi-insulating substrate is also studied. It is shown that the kink-related sidegating is less remarkable in the case with lower acceptor density in the substrate. Potential dependence of sidegating effects on the sidegate (backgate) position is also discussed.     

Assessment of vulnerable plaque composition by matching the deformation of a parametric plaque model to measured plaque deformation

Intravascular ultrasound (IVUS) elastography visualizes local radial strain of arteries in so-called elastograms to detect rupture-prone plaques. However, due to the unknown arterial stress distribution these elastograms cannot be directly interpreted as a morphology and material composition image. To overcome this limitation we have developed a method that reconstructs a Young's modulus image from an elastogram. This method is especially suited for thin-cap fibroatheromas (TCFAs), i.e., plaques with a media region containing a lipid pool covered by a cap. Reconstruction is done by a minimization algorithm that matches the strain image output, calculated with a parametric finite element model (PFEM) representation of a TCFA, to an elastogram by iteratively updating the PFEM geometry and material parameters. These geometry parameters delineate the TCFA media, lipid pool and cap regions by circles. The material parameter for each region is a Young's modulus, EM, EL, and EC, respectively. The method was successfully tested on computer-simulated TCFAs (n = 2), one defined by circles, the other by tracing TCFA histology, and additionally on a physical phantom (n = 1) having a stiff wall (measured EM = 16.8 kPa) with an eccentric soft region (measured EL = 4.2 kPa). Finally, it was applied on human coronary plaques in vitro (n = 1) and in vivo (n = 1). The corresponding simulated and measured elastograms of these plaques showed radial strain values from 0% up to 2% at a pressure differential of 20, 20, 1, 20, and 1 mmHg respectively. The used/reconstructed Young's moduli [kPa] were for the circular plaque EL = 50/66, EM = 1500/1484, EC = 2000/2047, for the traced plaque EL = 25/1, EM = 1000/1148, EC = 1500/1491, for the phantom EL = 4.2/4 kPa, EM = 16.8/16, for the in vitro plaque EL = n.a./29, EM = n.a./647, EC = n.a./1784 kPa and for the in vivo plaque EL = n.a./2, EM = n.a./188, Ec = n.a./188 kPa.     

热处理和淬火的未掺杂半绝缘LEC GaAs的均匀性

对未掺杂原生ＬＥＣＳＩＧａＡｓ单晶在５００～１１７０℃温度范围进行了单步、两步和三步热处理及淬火，研究了这种热处理对ＥＬ２分布的影响，并检测了位错和Ａｓ沉淀的变化。结果表明，６５０℃以上温度的热处理可以改善ＥＬ２分布均匀性，且在６５０～９５０℃温度范围的热处理中，ＥＬ２均匀性的改善与热处理后的降温速率无明显联系。此外，两步或三步热处理的样品中ＥＬ２分布甚至比单步热处理样品中更优。９５０℃以下的热处理和淬火对位错和Ａｓ沉淀无明显影响。但是１１７０℃热处理井淬火后位错密度增加大约３０％，Ａｓ沉淀消失。对经１１７０℃淬火的样品再进行８０Ｏ℃或９５０℃的热处理，Ａｓ沉淀重新出现。ＥＬ２分布的变化可能与点缺陷、位错和Ａｓ沉淀的相互作用有关。文中提出了这种相互作用的模型，利用该模型可解释不同条件热处理后ＥＬ２分布的变化。     

Interface Electron Traps as a Source of Anomalous Capacitance in AlGaN/GaN Heterostructures

We studied by modeling and simulation how deep traps at the AlGaN/GaN heterostructure interface influence the shape of capacitance–voltage (C–V) curves of the heterostructure. Assuming donor and acceptor type of traps, we found differences in the C–V curves for sharp energy interface states or continuously distributed states with the same total concentration for the acceptor-type interface states. The background doping concentration of GaN had only a marginal influence on the shape of the C–V curves. We observed that an anomalous capacitance peak occurred for the continuous distribution of traps in the bandgap; a similar peak had been observed in experiment. We also saw that the capacitance curves shifted slightly to the right or to the left depending on the GaN doping concentration. A remarkable difference was found between the capacitance curves for the structures with the sharp acceptor trap level and continuous distribution of traps. For donor-type interface states, we found practically no influence on C–V curves since they remain populated and charge neutral during the measurement.     

ZnO量子点／SiO2复合器件的可调控电致发光研究

在不同浓度的SiO2乙醇溶液中制备了一系列ZnO量子点／SiO2复合材料,通过匀胶方法将其制备成复合薄膜器件。器件的电致发光（EL）随着SiO2浓度的增加逐渐蓝移。通过实验,探索了发生蓝移的机制。选取一种ZnO量子点／SiO2复合材料均匀混入不同质量的纯SiO2后,测试结果表明,该蓝移现象不是SiO2自身发光引起的。通...     

Growth of P-type Znse by metalorganic molecular beam epitaxy using metal Zn and dimethylselenide

This paper describes metalorganic molecular beam epitaxy (MOMBE) of p-type ZnSe using metal zinc, pre-cracked metalorganic dimethylselenide, and microwave-excited nitrogen plasma as sources. Optical, structural, and electrical properties of the p-type ZnSe layers have been investigated. At present, maximum net acceptor concentration N_a-N_d is 3 x 10¹⁷ cm^-3 without any post-growth annealing. This is the highest acceptor concentration ever reported for MOMBEgrown p-type ZnSe doped with nitrogen plasma, but photoluminescence and deep level transient spectroscopy suggest that acceptors are highly compensated and the reduction of compensating defects is a key to further increase the acceptor concentration.     

GaN基微米LED大注入条件下发光特性研究

利用变注入强度的电致发光(EL)测试和数值模拟方法研究了微米LED大注入条件下的发光特性。EL测试结果显示,微米LED(10μm)在工作电流密度高达16kA/cm2时光功率密度输出未饱和,同时不存在明显的由于自热效应引起的发光波长红移。和300μm LED相比,相同注入水平下,10μm LED的EL峰值波长相对蓝移,表明微米LED中存在应力弛豫,10μmLED相对300μm LED应力弛豫大了约23%。APYSY模拟发现,由于应力弛豫和良好的电流扩展,微米LED中电流分布和载流子浓度更加均匀,这种均匀的分布使得微米LED具有高的发光效率,同时能够承受高的电流密度。     

Efficient exciplex emission from intramolecular charge transfer material

New exciplexes formed between a typical intramolecular charge transfer (ICT) material (bis[4-(9,9-dimethyl-9,10-dihydroacridine)phenyl]sulfone (DMAC-DPS)) and a series of electron donor and acceptors in donor:acceptor system have been systematically demonstrated. It is found that such ICT materials could form exciplex with both standalone electron donor and acceptor materials with itself as acceptor and donor components, which is based on the presence of both donor and acceptor species in the ICT material. The emission spectra of exciplex OLEDs based on ICT materials could be regularly tuned ranging from blue to yellow color by changing energy level alignment between ICT and standalone donor/acceptor materials. Among these exciplexes, DMAC-DPS:PO-T2T combination offered the highest exciplex EL performance, with its peak external quantum efficiency, luminance and current efficiency of 9.08%, 35,000 cd/m² and 30 cd/A, respectively. On the other hand, we also found that the exciplex efficiency was insensitive with the weight ratio between ICT material and acceptor, which means ‘doping’ of ICT material into the acceptor. Our finding extend the usage and selection scope of the TADF material.     

On the Evolution of Carrier Distribution and Wavelength Switching in Asymmetric Multiple Quantum-Well Lasers

The evolution of the carrier distribution with current in two different asymmetric multiple quantum laser structures was studied experimentally through measurements of electroluminescence (EL). The EL was measured through the substrates of lasers and provided information about the carrier distributions. The carrier concentration was observed to increase with current both below and above threshold, presumably owing to the change of threshold conditions. The switch of the lasing wavelength from long to short wavelength was explained by inhomogeneous broadening of the gain of the wells and by incomplete clamping of the carrier concentration above threshold, as inferred from the measured EL and gain spectra. The role of thermal effects was investigated by comparing the laser performance under continuous-wave and pulsed operation     

Numerical analysis of the frequency-dependent output conductance ofGaAs MESFET's

The small-signal output conductance of GaAs MESFETs on semi-insulating substrate is studied using two-dimensional numerical analysis. Frequency-, temperature-, and drain-bias-dependent behaviours of the output conductance are analysed. It is confirmed that the bulk EL2 traps contribute significantly to the low-frequency-dependent behavior of the output conductance. Devices with different background trap concentrations and acceptor concentrations were analyzed and compared. For devices with higher trap concentrations, the output conductance is lower but exhibits stronger frequency dependence     

Numerical analysis of the looping effect in GaAs MESFET's

The looping effect in the I_D-V_D (drain-current-drain-voltage) characteristics of GaAs MESFETs on semi-insulating substrates has been studied using a two-dimensional numerical analysis. Both the transient and the steady-state behaviors of the looping phenomenon were simulated. Peak voltage- and frequency-dependent behaviors of the looping effect are analyzed. The I_D-V_D loop is due to the difference in the distribution of ionized EL2 concentration when the drain voltage rises and falls because of the trapping process of EL2s. The output conductance is also found to be frequency-dependent and is explained by the frequency-dependent modulation of the potential barrier height at the channel/substrate interface due to the drain-voltage variation