Polarity dependent oxide defects located using liquid crystals

Liquid crystals have been used to study, non-destructively, the localized regions of high conductivity known to be present in thin layers of silicon dioxide grown thermally on n type silicon. The polarity dependence of the turbulence in the liquid crystals, together with the growth in the number of defects with time suggests that mobile impurity ions play an important role.     

低电阻率高透过率TAZO透明导电膜的制备及性能

利用直流磁控溅射工艺,在水冷玻璃衬底上制备了透过率高、电阻率相对较低的钛铝共掺杂ZnO(TAZO)透明导电膜。用XRD和SEM等研究其结构、应力和光电性能与靶基距之间的关系。结果表明:TAZO薄膜为六方纤锌矿结构的多晶薄膜,且具有c轴择优取向。当靶基距为42mm时,薄膜样品晶格畸变最小,具有最小压应力(绝对值)0.270GPa,同时具有最小方块电阻4.21?/□;靶基距为48mm时,薄膜样品具有最小电阻率3.09×10–4?·cm。所有薄膜样品的可见光区平均透过率都超过了91%。     

Temperature dependent study of carbon-doped InP/InGaAs HBT's

We report on a temperature dependent study of the dc and the microwave performance of carbon-doped InP/In_0.53Ga_0.47 As heterojunction bipolar transistors (HBT's). The turn on voltage increased 114% and the dc current gain decreased 25% as the temperature was reduced from 300 K to 33 K. Under high-current injection, there was a 29% increase in the current gain cutoff frequency of these devices as the temperature was lowered from 300 K to 77 K. By investigating the operation of HBT's at cryogenic temperatures, increased understanding of the mechanisms of carrier transport in these devices can be obtained, and this may lead to improvements in device performance     

基于Tchebichef图像矩的氧化锌太赫兹光谱定量研究

为了提高多组分混合物太赫兹光谱定量分析的准确性和稳定性, 将Tchebichef图像矩结合偏最小二乘回归(PLS)的建模方法引入到太赫兹光谱定量分析中, 以橡胶添加剂氧化锌、白炭黑与丁腈橡胶的混合物为实验样本, 对混合物中的氧化锌进行定量分析。获取样本太赫兹吸光度数据后, 用3维光谱自构建方法构建样本的3维光谱, 利用Tchebichef图像矩提取样本3维光谱灰度图的特征信息, 然后用PLS建立定量模型对氧化锌进行定量分析。结果表明, 由本方法得到的样本预测集相关系数和均方根误差分别为0.9993和0.0351, 与用PLS和支持向量回归直接对吸光度数据进行建模的方法相比, 结果更加准确和稳定。本方法能够对混合物中氧化锌进行准确、稳定的定量分析, 为多组分混合物太赫兹光谱定量分析提供了新思路。     

Temperature dependence of specific contact resistivity

The temperature dependence of specific contact resistivity has been measured over the range 77-380 K for W contact to both B- and P-doped silicon. A range of surface concentrations have been investigated. In general, ρcis slightly more weakly temperature dependent than has been predicted. There appears to be no fundamental barrier to obtaining low-resistance contacts for low-temperature (<100 K) device operation. Contact resistivity to very heavily P-doped surfaces actually decreases with decreasing temperature, in agreement with predictions.     

Temperature dependent resistivity of platinum-carbon composite nanowires grown by focused ion beam on SiO2/Si substrate

Experimental studies of the temperature dependent resistivity of platinum nanowires grown on an oxidised silicon wafer by using focused ion beam (FIB) have been made. A series of 4-terminal resistivity measurements were carried out in the temperature range 50-300 K on single nanowires of width and thickness ∼100 nm grown by decomposition of an organometallic precursor using Ga⁺ ions of different accelerating voltages from 10 keV to 30 keV. Energy dispersive X-ray spectroscopy showed the nanowires to be composed of more than 60% by volume of carbon, the remainder being principally platinum and gallium. The exact composition depends on the accelerating voltage of the ions used. There is clear evidence from cross-sectional microscopy that the material is a composite consisting of a metallic phase present in the form of nanoscale clusters, randomly distributed in a matrix of carbon. Electrical measurements are consistent with this, showing a critical volume concentration for conduction, which is typical of electron transport in composites with percolating metal phase. Results show an unexpectedly high sensitivity of the temperature dependence of resistivity near the critical volume concentration, which has been explained to arise from thermal strain effects. The anomalous temperature/strain effects observed in this investigation might be exploited in temperature measurement and strain sensor applications.     

Composite materials based on nanostructured zinc oxide

Composites formed from ZnO nanorods in combination with CuO or Ag nanoparticles are produced by the deposition of CuO or Ag nanoparticles onto ZnO nanorod arrays grown by the hydrothermal technique. The CuO nanoparticles are synthesized by the vacuum thermal deposition of a Cu layer followed by vacuum annealing at a temperature of 350°C for 1 h. CuO particles covered with a layer of nanoneedles are obtained. The current-voltage characteristics of the ZnO/CuO layers are indicative of the formation of a p-n junction. The ZnO/Ag composites are produced by the electrical deposition of Ag nanoparticles synthesized in an aqueous solution of silver nitrate and sodium citrate. The surface morphology and the optical and electrical properties of the samples are studied.     

Luminescence of zinc oxide nanorods

The spectra of spontaneous and stimulated emission of ZnO nanorods grown by two low-temperature procedures are studied. Stimulated emission at 385 nm is observed at room temperature in CVD ZnO nanocrystals pumped by the nitrogen laser radiation at the wavelength 337 nm. The threshold pumping power density for lasing exitonic recombination is ～600 kW/cm².     

In_2O_3和ZnO混合薄膜的化学腐蚀特性研究

利用直流磁控溅射在未加热的BK-7玻璃基片上沉积In2O3与ZnO混合(IZO)薄膜,通过原子力显微镜(AFM)、分光光度计和四探针法研究IZO薄膜在HCl溶液中不同腐蚀时间前后的表面形貌以及光电性质的变化。结果表明:随着腐蚀时间的增加,薄膜的表面均方根粗糙度(RMS)和方块电阻(Rs)都呈现先增后减再增的现象;而薄膜的光学透射率则是先减后增再减。由于ZnO比In2O3更容易在HCl溶液中进行腐蚀,使得样品经腐蚀后出现孔洞结构,孔宽与孔深都随着腐蚀时间的增加而增大,这种具有纳米孔洞结构的透明导电薄膜在未来的光电子器件有潜在应用。     

氧化锌压敏陶瓷的微波烧结工艺研究

微波烧结技术因能改善被烧结材料的微观结构和性能,已经成为材料制备领域里新的研究热点。本文以氧化锌压敏陶瓷为研究对象,以Bi_2O_3含量、升温速率、烧结温度、保温时间为四要素对陶瓷的微波烧结工艺设计了正交实验。研究发现,微波烧结所得样品与传统烧结样品相比,其漏电流和非线性系数均得到了优化。通过对正交实验数据的分析,得出了针对每个性能的最优工艺参数及各要素对各性能影响的主次顺序,最后经综合考虑确定了微波烧结氧化锌压敏陶瓷的最优工艺参数,得到了压敏电位梯度为362. 3 V/mm,非线性系数为50. 24,漏电流密度为1. 55×10~(-6)A/cm~2,密度为5. 603 g/cm~3的氧化锌压敏陶瓷。缩短了烧结时间,优化了陶瓷的性能。     

Aligned arrays of zinc oxide nanorods on silicon substrates

Experimental data on the elemental vapor-phase synthesis of aligned arrays of ZnO nanorods on Si substrates are summarized. A model of the self-catalytic growth of ZnO nanorods via the vapor-liquid-crystal mechanism, in which liquid Zn droplets serve as a catalyst for oriented growth, is presented. The method developed in the study provides a means for the deposition of aligned arrays of ZnO nanorods onto differently oriented Si substrates without the preliminary deposition of a metal catalyst film or a thin layer of ZnO nuclei. The influence of various factors on the growth rate, dimensions, shape, and ordering of ZnO nanorods is considered. The ZnO nanorods produced in the study are high-purity single crystals with a low content of point defects and, thus, are suitable for practical use in optoelectronics as well as in sensor and microsystem technologies.     

Effect of externally applied pressure on zinc oxide varistors

A study of the effect of uniaxial pressure on the I-V response of zinc oxide varistors has shown a pressure sensitivity in both prebreakdown and breakdown regions. The general observation is that the conductivity increases with pressure, the effect being more pronounced in the prebreakdown region. Data are in general agreement with the phenomenological model given by Schwertz and Mazenko. Data are also treated on the basis of Schottky barrier and tunneling theories. According to this analysis, the barrier height is found to decrease with pressure. At the time this work was performed, M. P. Mathur was a Consultant for the Westinghouse Electric Corporation, Pittsburgh, Pennsylvania.     

Temperature dependent photoluminescence of porous InP

Temperature dependent photoluminescence (PL) spectra of porous InP prepared by wet-electrochemical techniques are presented. Compared to the PL spectra of the bulk InP wafer measured at the corresponding temperatures, two peaks are observed in porous InP. One peak, which dominates at temperatures above 150 K, shows blue shift about 14 meV, while the other peak, which dominates at temperatures below 120 K, shows red shift about 33 meV. Quantum confinement effect is assumed to be the origin of the blue shifted PL. The red shifted PL emission is very sensitive to chemical treatment and is suggested to be due to the radiative recombination via surface states.     

A first principle study of pressure-induced effects on phase transitions,band structures and elasticity of zinc oxide

Using the first-principles projector-augmented wave (PAW) method, the pressure induced effects on solid–solid phase transition, electronic band structures and elasticity of zinc oxide are investigated. The four possible structures are considered here, including rocksalt (B1), CsCl (B2), zinc blende (B3), and wurtzite (B4). It is found that structural properties and phase transition points by the PBEsol method are better than those computed using the standard local density approximation and Perdew, Burke and Ernzerhof functionals. Moreover, using the hybrid HSE06 functional, the band structures around phase transition points are displayed. The predicted fundamental gaps of the four considered structures provide improvements over directly density functional theory calculations. Meanwhile, the effective masses for the electrons in the conduction band and the holes in the valence band are derived. Furthermore, the elastic abnormal behavior is achieved around the phase transition points. For B4, B1 and B2 structures, the longitudinal and transverse sound velocities are evaluated along significant symmetry directions with pressure, and it still awaits experimental confirmation.     

Laser spectra of the complex structures of zinc oxide

The laser spectra of the ZnO powder and complex structures and the time evolution of the spectra are studied at room temperature using low- and high-level pumping with nanosecond laser pulses. The ZnO complex structures consist of a dense core and a loose sheath formed of tetrapod crystallites. The nature of the laser modes that contribute to the spectra is discussed. A simplified model of such modes is proposed and analyzed. It is demonstrated that, in the powder, the modes are densely concentrated in the UV range of the zinc-oxide emission. In the complex structure, several laser modes are spectrally separated. We conclude that the modes are related to the tetrapods.     

Temperature dependence of resistivity and hole conductivity mobility in p-type silicon

A new method is employed to determine the temperature dependence of the resistivity and hole conductivity mobility of p-type silicon. This method involves the use of an aluminum-on-p-Si ohmic diode and a magnesium on p-Si Schottky barrier diode on the same silicon chip. The resistivity is determined from the Al/p-Si ohmic diode. The hole concentration is evaluated from the C-V data of the Mg/p-Si Schottky barrier diode. The conductivity mobility is then computed from the resistivity and hole concentration data. The following ranges are covered: 77–300 K, 0.4–100 ohm-cm and 5 × 10¹⁶?2 × 10¹⁴ holes/cm³ at room temperature.     

Electrodeposited zinc oxide arrays with the moth-eye effect

The materials of modern photovoltaic cells exhibit significant light reflection which is avoided using antireflective coatings. The possibility of fabricating antireflective coatings such as nanoscale zinc oxide arrays with a parabolic profile by pulsed electrochemical deposition from aqueous electrolytes is shown for the first time. The effect of the deposition conditions on the optical properties of oxide arrays is studied using spectrophotometry. The structural characteristics are analyzed by X-ray diffraction data. The morphology of the grown arrays is determined by atomic-force microscopy. Optimization of the pulsed electrodeposition conditions allows correction of the parabolic nanonipple sizes, thus providing the fabrication of antireflective coatings based on electrodeposited zinc oxide arrays with the moth-eye effect, applicable to photovoltaic cells.     

Temperature and wavelength dependent properties of multiplate reflectors

This paper describes a new approach to the design of multi-element resonant reflectors. These mirrors provide an effective means of controlling the spectral spread of high-gain laser oscillators, but the complexity of the reflectivity as a function of wavelengthR (lambda)has made the design of these systems rather difficult. However, we show that by making a two-dimensional plot of reflectivity versus wavelength and temperature, one can obtain several parameters of the system immediately that anR (lambda)plot does not reveal. Simple algebraic expressions for some of these parameters are given, and a configuration for an improved four-element wavelength selector based on these results is presented.     

Time dependent breakdown of ultrathin gate oxide

Time dependent dielectric breakdown (TDDB) of ultrathin gate oxide (<40 Å) was measured for a wide range of oxide fields (3.4<|E_ox|<10.3 MV/cm) at various temperatures (100⩽T⩽342°C). It was found that TDDB of ultrathin oxide follows the E model. It was also found that TDDB t₅₀ starts deviating from the 1/E model for fields below 7.2 MV/cm. Below 4.8 MV/cm, TDDB t₅₀ of intrinsic oxide increased above the value predicted by the E model obtained for fields >4.8 MV/cm. The TDDB activation energy for this type of gate oxide was found to have linear dependence on oxide field. In addition, we found that γ (the field acceleration parameter) decreases with increasing temperature. Furthermore, it was found that testing at high temperatures (up to 342°C) and low electric field values did not introduce new gate oxide failure mechanism. It is also shown that TDDB data obtained at very high temperature (342°C) and low fields can be used to generate TDDB model at lower temperatures and low fields. Our results (an enthalpy of activation of 1.98 eV and dipole moment of 12.3 eÅ) are in complete agreement with previous results by McPherson and Mogul. Additionally, it was found that TDDB is exponentially dependent on the gate voltage     

FIB and TEM observations of defects in hot-dip zinc coatings

The characteristic ability of FIB (focused ion beam) fabrication to remove materials from a very small and/or precisely located slab using an accelerated Ga ion beam were employed to prepare cross-sectional thin films of zinc-coated steel sheets composed of Fe-Zn intermetallic compounds. A few defects observed frequently on the galvannealed (GA) coating surface were analyzed. Streaky marks indicated the rich concentration of oxides at the interface between the galvannealed coating and the steel substrate. The annealing experiment indicated the existence of Mn and Si oxides on the steel substrate. The grain size of ferrite in the extreme surface of the substrate was smaller as compared with conventional IF (Interstitial Free) steels. Furthermore, some superlattice spots were observed at the fine ferrite grain. Defects that are termed 'wavy pattern' and 'dross' were also analyzed by the combination of the FIB and TEM (Transmission Electron Microscope) techniques.