氧气氛中p-GaN/Ni/Au电极在相同温度不同合金时间下的欧姆接触形成机制和扩散行为

用卢瑟福背散射/沟道技术研究了p-GaN上的Ni/Au电极在氧气氛下相同合金温度(500℃)不同合金时间后的微结构演化,以揭示欧姆接触的形成机制.利用背散射随机谱和RUMP模拟程序研究了电极金属之间的互扩散,用沟道谱探测了电极金属中的氧分布.结合不同合金时间下比接触电阻ρ_c的变化,发现随着合金时间的延长比接触电阻持续降低,在合金时间60 s后降低的速度减慢, Au扩散到GaN的表面,在p-GaN上形成外延结构,O向电极内部扩散反应生成NiO对降低ρ_{关键词： GaN 卢瑟福背散射/沟道 欧姆接触}     

Ni/Ag/Ti/Au与p-GaN的欧姆接触性能及光反射率

研究了不同Ni厚度的Ni/Ag/Ti/Au电极在不同退火温度和退火气氛下与p-GaN之间的欧姆接触性能以及电极的光反射率的变化.采用矩形传输线模型对各电极的比接触电阻率进行测算,利用分光光度计对电极在不同波长下的反射率进行测量.结果表明,Ni金属层的厚度越小,电极的光反射率越高,而Ni层厚度对比接触电阻率的影响较小;当退火温度高于400℃后,电极的光反射率降低,在氧气氛围中退火后光反射率比在氮气中退火后下降更加明显.但在氧气氛围中退火有利于减小比接触电阻率.综合考虑接触电阻和光反射率,电极Ni(1 nm)/Ag/Ti/Au在400℃氧气中快速退火后得到了较好的结果,其比接触电阻率为5.5×10-3Ω·cm2,在450 nm处反射率为85%.利用此电极制作了垂直结构发光二极管(LED)器件,LED在350 mA注入电流下,工作电压为3.2 V,发光功率为270 mW,电光转换效率达到24%.     

低接触电阻率Ni/Ag/Ti/Au反射镜电极的研究

研究了Ag的厚度、退火时间、沉积温度对于Ni/Ag/Ti/Au电极的反射率及与p-GaN欧姆接触性能的影响. 利用分光光度计测量反射率, 采用圆形传输线模型计算比接触电阻率. 结果表明: 随着Ag厚度的增加, Ni/Ag/Ti/Au电极的反射率逐渐增大; 在氧气氛围中, 随着退火时间从1 min增至10 min, 300 ℃退火时, 比接触电阻率持续下降, 而对于400-600 ℃退火, 比接触电阻率先减小后增大; 在300和400 ℃氧气中进行1-10 min 的退火后, Ni/Ag/Ti/Au的反射率变化较小, 退火温度高于400 ℃时, 随着退火时间的增加, 反射率急剧下降; 在400 ℃氧气中3 min退火后, 比接触电阻率可以达到3.6×10^-3 Ω·cm². 此外, 适当提高沉积温度可以增加Ni/Ag/Ti/Au的反射率并降低比接触电阻率, 沉积温度为120 ℃条件下的Ni/Ag/Ti/Au电极在450 nm处反射率达到90.1%, 比接触电阻率为6.4×10^-3 Ω·cm². 综合考虑电学和光学性能, 在沉积温度为120 ℃下蒸镀Ni/Ag/Ti/Au (1/200/100/100 nm)并在400 ℃氧气中进行3 min退火可以得到较优化的电极. 利用此电极制作的垂直结构发光二极管在350 mA电流下的工作电压为2.95 V, 输出光功率为387.1 mW, 电光转换效率达到37.5%.     

重费密子系统CeCu6-xNix的极低温电阻研究

CeCu₆是一种重费密子系统,采用Ni替代Cu研究磁性原子掺杂的多晶样品CeCu_6-xNi_x(x=0.00,0.05,0.10,0.15,0.20)在极低温下的电阻随温度的变化规律.实验结果表明,随着Ni原子掺杂量的增加,电阻的规律发生变化.在500mK以下,x≈0.1的样品电阻与温度呈线性关系,表现出非费密液体行为,而其他样品皆为典型的费密液体,x≈0.1是其临界掺杂成分.对比用Au替代的情况,临界掺杂成分也是0.1,但Au掺杂是靠体积膨胀来改变合金的基态性质,而Ni掺杂则是因其磁性造成对合金基态性质的影响 关键词： 重费密子 临界掺杂 非费密液体     

Ni/Au与N掺杂p型ZnO的欧姆接触

研究了Au,In,Ni/Au三种不同金属膜与N掺杂p型ZnO的接触特性,发现Ni/Au双层膜更适合作为其欧姆电极材料,并比较了不同气氛和不同温度退火对Ni/Au电极的影响.发现在O₂中退火电极性能发生蜕变,而在N₂中退火性能得到改善.指出即使在N₂中退火,退火温度的选择也是至关重要的,本实验在400℃,氮气气氛下退火150s,得到了较好的欧姆接触特性.     

没食子酸还原法制备金银合金纳米粒子及其吸收光谱研究

用没食子酸一步液相还原制备粒度均匀和性质稳定的Au-Ag合金纳米粒子,研究在不同反应温度和Au／Ag摩尔比下Au-Ag合金纳米粒子的吸收光谱特性。实验结果表明Au-Ag合金纳米粒子仅有1个吸收峰,介于纯Ag和纯Au纳米粒子的吸收峰之间,且随着反应温度的提高,合金纳米粒子的最大吸收峰位逐渐蓝移,吸光度增加,半峰宽变窄。随着Au/Ag摩尔比的增加,合金纳米粒子的最大吸收峰位红移,且与其所含Au摩尔百分数呈线性关系。HRTEM表征结果说明制备的Au/Ag合金纳米粒子近球形、粒度均匀、无包覆现象。EDX分析结果证实单个纳米粒子由Au和Ag组成,其元素组成比与参加反应的Au/Ag摩尔比接近。     

RF磁控溅射条件对ZnO薄膜结构的影响

采用RF磁控溅射法在Si（001）衬底上制备ZnO薄膜。研究发现了工作中溅射频率、氧气和氩气流量比对样品结构的影响。样品的XRD图谱显示了强的（002）ZnO衍射峰，表明ZnO薄膜为c轴高取向生长。比较不同条件下制备的ZnO薄膜，研究发现当氧气和氩气的流量比相同时，随着溅射功率的增加，样品的（002）衍射峰增强，半高全宽变小。而当溅射功率相同时，随着氧气和氩气的流量比增加，样品的（002）衍射峰也增强，半高全宽同样变小。此外，本文还分析了溅射工艺和薄膜晶体质量之间关系，发现在相同的功率条件下，溅射率低时晶粒尺寸更大且薄膜的结晶性更好。     

TiAl3 和Ti/TiAl3 非合金化电极n型GaN欧姆接触的实现

在不进行合金化的情况下,首次直接采用TiAl3合金材料作为金属接触电极.在蓝宝石衬底上生长的n型载流子浓度为2×1018 cm-3的GaN上,成功地得到低接触电阻的欧姆接触,并由环形传输线模型方法测得比接触电阻率为3×10-5 Ω*cm2.与通常n型欧姆接触采用的Ti/Al双层结构比较,TiAl3合金结构更容易形成非合金化的n型欧姆接触.在此实验基础上,进一步分析了N空位和界面层处的TiAl3在形成非合金化或低温退火欧姆接触中发挥的作用,由此设计的Ti/TiAl3/Ni/Au接触结构,在TiAl3合金结构基础上明显地降低了接触电阻率.     

退火温度和退火气氛对Ni/Au与p-GaN之间欧姆接触性能的影响

研究了不同退火温度和气氛对Ni/Au与p-GaN之间欧姆接触性能的影响. 采用圆形传输线模型方法得到不同退火温度和不同退火气氛下的比接触电阻率. 结果表明, 较适宜的退火温度为500 ℃左右, 退火温度太高或太低都会导致比接触电阻率的增大; 较适宜的退火气氛为适量含氧的氮气气氛, 且氧气含量对比接触电阻率大小的影响并不显著. 经过对退火条件的优化, 得到的比接触电阻率可达7.65×10^-4 Ω·cm². 关键词： p-GaN 欧姆接触 圆形传输线模型 快速热退火     

用光电子能谱研究CdTe太阳电池的背接触特性

CdTe太阳电池的背电极须采用高功函数金属。通过采用光电子能谱(XPS)分析了高功函数金属Au和Ni分别作为背电极的CdTe太阳电池背接触特性,发现在背电极剥离后,Au在ZnTe/ZnTe∶Cu背接触层表面以Au单质形式存在,扩散深度较浅;Ni扩散到ZnTe/ZnTe∶Cu复合层的深度比Au大,且大多呈离子态,与ZnTe/ZnTe∶Cu复合层中的富Te离子形成Ni_xTe,提高了掺杂浓度,使电池性能获得改善。在两样品中还发现,不论是Te的峰还是Zn的峰,其峰的位移变化都很小,说明两样品中Te和Zn的存在形式没有发生变化。     

Self-organization of five species in a cyclic competition game

Cyclic competition game models, particularly the “rock–paper–scissors” model, play important roles in exploring the problem of multi-species coexistence in spatially ecological systems. We propose an extended “rock–paper–scissors” game to model cyclic interactions among five species, and find that two of the five can coexistent when biodiversity disappears, which is different from the “rock–paper–scissors” game. As the number of fingers is five, we named the new model the “fingers” game, where the thumb, forefinger, middle finger, ring finger, and little finger cyclically dominate their subsequent species and are dominated by their former species. We investigate the “fingers” model in two ways: direct simulations and nonlinear partial differential equations. An important finding is that the number of species in a cyclic competition game has an influence on the emergence of biodiversity. To be specific, the “rock–paper–scissors” model is in favor of maintaining biodiversity in comparison with the “fingers” model when the variables (population size, reproduction rate, selection rate, and migration rate) are the same. It is also shown that the mobility and reproduction rate can promote or jeopardize biodiversity.     

Experimental study on downstep in Chinese intonation

Downstep in pitch contour of Chinese Putonghua is examined using subtly designed sentences by controlling tone combinations. The results show both automatic and nonautomatic downstep phenomena exist in Chinese. In non-automatic downstep, low tones compress downwards the pitch range of the following syllables. and the main influence of downstep is on topline. Low tone not only lower the topline behind it, but also raise the high tones before it, the effects are compatible with each other. In automatic downstep, the topline of pitch contour in intonational phrase is presented as a linear downtrend, but it differs among speakers due to the effect of personal stress practice. In comparison with downstep phenomenon in other tone or non-tone languages, the downstep ratio in Chinese is not constant, and the domain of downstep is not limited within the adjacent tones.     

Contrastive analysis on tone between Putonghua and Taiwan Mandarin

The differences of the pitch and duration of Chinese syllables between Putonghua （PTH） and Taiwan Mandarin （TM） were studied. The speech materials to be used are not only isolated syllables, but also sentences. The results reveal that： For the isolated syllables, T1 and T2 in TM are influenced by Minnan dialect, therefore their pitch are lower than those in PTH. T3 is fall-rise in PTH, while it is fall in TM. Moreover, the syllable duration sequence for different tone is T3〉T2〉T1〉T4 in PTH, while it is T1〉T2〉T3〉T4 in TM. For the syllables in sentences, T2 is mid-rise in PTH, while it is mid-level in TM. And the T3 is longer than T4 but shorter than T1 or T2 in PTH, while it is the shortest in TM. Furthermore the effects of prosodic phrase boundary on duration for different tones are almost the same in PTH, but the lengthening part of T1 or T2 is longer than that of T3 or T4 in TM.     

Abelian-Higgs phase of SU(2) QCD and glueball energy

It is shown that SU(2) QCD admits an dual Abelian-Higgs phase, with a Higgs vacuum of a type-Ⅱ superconductor. This is done by using a connection decomposition for the gluon field and the random-direction approximation. Using a bag picture with soft wall, we presented a calculational procedure for the glueball energy based on the recent proof for wall-vortices [Nucl. Phys. B 741(2006)1].     

Signal generation in an isotropic medium in scanning electron acoustic microscope

Based on the research in Ref. [5][Materials Science and Engineering, 1989; A122： 57 63], an improved model of heat source is set up, the different modes of Lamb wave in an isotropic sample generated by a chopped electron beam at frequency f are obtained with integral transform and normal function expansion method, and the output signal of PZT coupled at the back surface of the sample is found out. The generation mechanism of SEAM （Scanning Electron Acoustic Microscopy） signal is discussed. It shows that the SEAM is a near field imaging technique with high spatial resolution and its best lateral spatial resolution is about 2√2α （α is the radius of the focused electron beam）. Some of experimental results of SEAM images are presented in the paper and it shows that the spatial resolution of SEAM is better than 0.5 μm and smaller than the thermal diffusion length of the sample. Therefore the character of near field imaging in SEAM is also proved experimentally.     

High efficiency filtering using two-dimensional photonic crystal coupled cavity structures

Transmission spectra of coupled cavity structures (CCSs) in two-dimensional (2D) photonic crystals (PCs) are investigated using a coupled mode theory, and an optical filter based on CCS is proposed. The performance of the filter is investigated using finite-difference time-domain (FDTD) method, and the results show that within a very short coupling distance of about 3λ, where λ is the wavelength of signal in vacuum, the incident signals with different frequencies are separated into different channels with a contrast ratio of 20 dB. The advantages of this kind of filter are small size and easily tunable operation frequencies.     

Real-time restoration of rotational blurred image using gradient-loading

The key to the restoration of rotational motion blurred image is how to restore the image under a low cost and to correct the irreversibility of the degradation function matrix.Based on the special qualities of degradation function matrix and precise deduction in space-domain, we present a new approach using gradient-loading for restoration of rotational blurred image.By easily adding a gradient operator, the irreversibility of the original matrix is corrected and can be applied for inverse filtering then.Gradientloading is the optimized approach which combines the advantages of both the approaches using constrained least square filtering and traditional diagonal-loading.Compared with the approach using least square filtering, its peak signal-to-noise ratio (PSNR) is improved from 3.18 to 6.46dB, while the computing time is reduced to 1/2-1/3.Experimental results demonstrate the effectiveness, noise-resistibility, robustness, and low complexity of this approach, which make it more suitable for real-time environment.     

All-Optical Logic Device Using Bent Nonlinear Tapered Y-Junction Waveguide Structure

We propose an all-optical logic device made of a bent tapered Y-junction waveguide with a Kerr-type nonlinear interface. It could provide an AND gate, OR gate, and exclusive-OR (XOR) gate. We could obtain different transmission results by adjusting the bending angle. The numerical simulation results show that the device functions as AND, OR, and XOR gates.     

Real-time, continuous-wave terahertz imaging by a pyroelectric camera

Real-time, continuous-wave terahertz (THz) imaging is demonstrated. A 1.89-THz optically-pumped farinfrared laser is used as the illumination source, and a 124 × 124 element room-temperature pyroelectric camera is adopted as the detector. With this setup, THz images through various wrapping materials are shown. The results show that this imaging system has the potential applications in real-time mail and security inspection.