Application of the Taguchi method for assessment of surface treatment procedures for Ti/n-type GaN contacts

Abstract

A Taguchi approach was used to appraise the relative importance of gallium nitride surface preparation on the processing of Ti/n-type GaN contacts. It is shown that a potassium hydroxide etch, silicon tetrachloride etch or hydrochloric acid clean prior to metal deposition can significantly improve the performance of the contact for the criteria of metal adhesion, contact resistance, electrical behaviour and across wafer uniformity.     

Synthesis and optical properties of nanocrystalline V-doped ZnO powders

This paper reports the synthesis and optical properties of nanocrystalline powders of V-doped ZnO (i.e. Zn_0.95V_0.05O, Zn_0.90V_0.10O, and Zn_0.85V_0.15O) by a simple sol–gel method using metal acetylacetonates of Zn and V and poly(vinyl alcohol) as precursors. Structure of the prepared samples was studied by X-ray diffraction, FTIR spectroscopy, and selected-area electron diffraction (SAED) analysis. The morphology of the powders revealed by SEM and TEM was affected by the amount of V, causing the formations of both nanoparticles and nanorods in the Zn_0.95V_0.05O sample, nanorods in the Zn_0.90V_0.10O sample, and nanoparticles in the Zn_0.85V_0.15O sample. The optical properties of the samples were investigated by measuring the UV–VIS absorbance and photoluminescence spectra at room temperature. All the samples exhibited UV absorption at below 400 nm (3.10 eV) with a well-defined absorbance peak at around 364 nm (3.41 eV) and 288 nm (4.31 eV). The band gap of the V-doped samples shows a decrease with increasing V concentration. The photoluminescence spectra of all the samples showed a strong UV emission band at 2.98 eV, a weak blue band at 2.82 eV, a week blue–green band at 2.56 eV, and a weak green band at 2.34 eV, which indicated their high structural and optical quality.     

Preparation and characterization of highly dispersed nanocrystalline rutile powders

A highly dispersed nanocrystalline rutile powder (NRP) having ultrafine and narrow-distributed diameters was successfully prepared via an improved conventional liquid one-step method by introducing dioctyl sulfosuccinate sodium salt (AOT) surfactant in the peptization reaction anaphase. The average grain size of the product is 10-20 nm. The effects of the titanium tetrabutoxide (Ti(OBu)₄) to ethanol volumetric ratio, the precipitation temperature, the peptization temperature and the presence of dioctyl sulfosuccinate sodium salt (AOT) on the preparation of NRP were studied. A new procedure for synthesizing NRP is proposed, and the optimum conditions for preparing NRP were obtained. The TEM, XRD, SEM and FT-IR results were also investigated in this work.     

Preparation and characterization of indium-doped tin dioxide nanocrystalline powders

The precursors of SnO₂ or In₂O₃/SnO₂ nanocrystalline powders have been prepared by the sol-precipitation method. The precursors are calcined at different temperatures to prepare SnO₂ or In₃O₃/SnO₂ nanocrystalline powders with different particle sizes. The reaction conditions, such as the concentration of reactants, the surfactant, pH value, the amount of indium oxide doped, and the reaction temperature and time, have been studied. The nanocrystallites are examined by differential thermal analysis (DTA)/thermogravimetric analysis (TGA), X-ray diffraction (XRD), IR spectroscopy and transmission electron microscopy (TEM).     

络盐法制备纳米晶掺铝氧化锌粉体

通过新复合络盐晶体(NH4)1.95(Zno.95Alo.05)(SO4)2·6H2O的合成证实了反应初始溶液中形成了络离子.研究了沉淀终点pH值对掺铝氧化锌(ZAO)粒径及产率的影响,以及锌离子总浓度对ZAO粒径的影响.结果表明:制备ZAO纳米晶粉体的最佳沉淀终点pH=7,最佳锌离子总浓度为0.3mol/L,所得ZAO粉体的一次晶粒平均尺寸约13nm.     

Preparation of nanocrystalline YSZ powders by the plasma technique

A plasma synthesis method has been devised to produce nanosize YSZ powders with various yttria contents. The powders are synthesized by introducing a mixture of coarse-grained zirconia and yttria into an r.f. inductively coupled plasma flame. The average particle size of the as-prepared powders is in the range 20–40 nm and the specific surface area is 18–50 m²g^–1. The phase and granulometric composition of the produced powders depend on the degree of evaporation of raw powders, reagent concentration in the gas flow and quenching rate, and on the content of Y₂O₃. Up to 5.5 mol% yttria, the major phase of nanosize powders is tetragonal ZrO₂, mostly as the non-transformable (t) form. For yttria contents higher than 6 mol%, the major phase is cubic ZrO₂.     

Consolidation,microstructure and mechanical properties of nanocrystalline metal powders

Nickel, iron and aluminum nanocrystalline powders prepared by the evaporation-condensation method were high pressure consolidated to densities close to the theoretical at room temperature and at 300°C. Microstructures of the materials obtained were characterized by employing scanning (SEM) and transmission (TEM) electron microscopy. Microhardness and yield stress of the materials fabricated from the elemental nanocrystalline powders were measured and compared to those of Ni, Fe and Al high pressure consolidated from the micron/submicron elemental powders, and of a nanocrystalline Ni-20 TiC composite processed via attrition milling of a nickel oxide (NiO)/TiC powder blend followed by the reduction of NiO and high pressure consolidation to full density.     

氮化镓粉末的合成及其结构性质的研究

在950℃氮化温度下,通过β-Ga2O3粉末与流动的NH3反应35min制备出GaN粉末.XRD、XPS、FTIR、TEM的测量结果表明GaN粉末是六角纤锌矿结构的单晶晶粒,其晶格常数a=0.3191nm,c=0.5192nm;在粉末表面,Ga和N两种元素比约为11;GaN晶粒的形状为棒状.     

掺铝氧化锌粉末的制备及其性能研究

采用溶胶凝胶燃烧合成法制备了ZAO(掺铝氧化锌)粉末,借助于DSC-TG、XRD、SEM、反射率测试、红外辐射率测试对制得的ZAO粉末的形貌、微观结构、激光吸收性能和红外辐射性能进行表征.研究结果表明,制备的ZAO粉末属于六方晶系纤锌矿结构.XRD分析表明煅烧温度提高到700℃后,ZA0的晶相形成的更好.SEM图中可以看出,随着Al离子的掺杂量增加,ZAO粉末的粒径越来越小,形状越来越不规则.反射率图谱表明,在900～1200nm波长范围,存在较强的激光吸收.红外辐射率测试表明ZAO粉末具有中等红外辐射率.     

Benzene-thermal synthesis and optical properties of CdS nanocrystalline

Solvent thermal process has been successfully applied to prepare nanocrystalline CdS via the reaction CdSO₄ with Na₂S₃ in benzene at 80–120 °C. It was found that solvent, temperature, and reactant have significant effect on crystal structure and particle size of CdS nanocrystalline. The results show that increasing of temperature and using of solvent of low dielectric constant are beneficial to prepare CdS nanocrystalline in hexagonal phase. The water content in the system not only induces the presence of cubic phase CdS nanocrystalline, but also leads to a particle size increase. The results demonstrate that both phase and particle size can be well controlled. As-prepared CdS nanocrystalline powders display obvious blue-shift characteristics.     

Synthesis and optical properties of single-crystalline GaN nanorods

Single-crystalline GaN nanorods were successfully synthesized on Si(1 1 1) substrates through ammoniating Ga₂O₃/Mo films deposited on the Si(1 1 1) substrate by radio frequency magnetron sputtering technique. The as-synthesized nanorods are confirmed as single-crystalline GaN with wurtzite structure by X-ray diffraction (XRD), selected-area electron diffraction (SAED) and high-resolution transmission electron microscopy (HRTEM). Scanning electron microscopy (SEM) displays that the GaN nanorods are straight and smooth with diameters in the range of 100-200 nm and lengths typically up to several micrometers. X-ray photoelectron spectroscopy (XPS) confirms the formation of bonding between Ga and N. The representative photoluminescence spectrum at room temperature exhibits a strong and broad emission band centered at 371.1 nm, attributed to GaN band-edge emission. The growth process of GaN nanorod may be dominated by vapor-solid (VS) mechanism.     

NiO纳米晶的制备和电化学性能

用溶胶-凝胶(Sol-Gel)工艺制备纳米NiO粉体,研究了烧结温度对其结构和电化学性能的影响.结果表明,以醋酸镍、柠檬酸、乙二醇为原料通过酯化-络合过程合成的凝胶,在烧结过程中在430℃完全分解并逐渐形成NiO纳米晶;随着烧结温度的升高,纳米NiO粉体的结构趋于完善、品粒尺寸逐渐增大,其电化学循环性能逐渐提高;在600℃烧结2 h可得到平均粒径约为40 nm、呈球形的NiO纳米晶颗粒.NiO纳米晶的首次和第10次充放电比容量分别高达850 mAh/g和471 mAh/g,具有良好的容量保持率,明显优越于用固相法制备的NiO粉体.     

Thermal properties of ball-milled nanocrystalline Fe,Co and Cr powders

Ball-milled Fe, Co and Cr powders have been investigated by differential scanning calorimetry to study the stored enthalpy and the origin of the enhanced specific heat in these materials. The samples were prepared of high purity powder of 40–50 μm initial particle size and milling times up to 1 month have been applied. The results of calorimetric measurements have been correlated with structural parameters (average grain size and dislocation density) obtained by high resolution X-ray diffractometry.     

纳米粉体制备8YSZ电解质工艺性能研究

实验研究了纳米粉体制备8YSZ电解质的固相烧结过程。根据阿基米德原理测瓷体密度；通过测定烧结前后瓷片尺寸，求出烧结线收缩；采用四端电极法测瓷体的电导率；使用扫描电子显微镜(SEM)观测样品微观形貌，并探讨了YSZ纳米粉体烧结的动力学过程。由于纳米颗粒尺寸较细、粒度分布均匀、无硬团聚和很好的球形度，使得烧结温度大幅度降低。实验表明，最佳烧结温度为1450℃，此时材料致密，相对密度在97％以上；气孔含量少、晶粒均匀，电导率高，1000℃时为0．162Ω^-1cm^-1，是理想的高温电解质材料。     

Structural and optical properties of GaN-based nanocrystalline thin films

We study the effect of annealing on structure, morphology and optical properties of nanocrystalline films of GaN, GaN:O and GaN:Mn prepared by ion assisted deposition on silicon, quartz and glassy carbon substrates. Blisters and holes having diameters proportional with the thickness of the film were observed in GaN:O deposited on silicon and glassy carbon. The Mn excess in GaN:Mn turns through annealing into Mn_xN_y islands. The degree of short- and intermediate-range order in the films was investigated by micro-Raman spectroscopy, extending to about 3 nm for gallium oxynitride films annealed to 973 K and to more than 10 nm in GaN samples. A diminished oxygen content following the annealing procedures on GaN:O samples is noticed from the reduced intensity of the oxygen mode at 1000 cm^− 1 in the Raman spectra. This observation is supported with X-ray photoemission spectroscopy measurements. The presence of oxygen at concentrations above 15at.% in the films leads to an abrupt nanocrystalline-amorphous transition.     

CdS半导体纳米晶的生长及其光谱研究

用玻璃沉淀技术制备了含过饱和CdS的玻璃固溶体,在一定条件下晶化处理使其长出CdS量子点,并采用了X射线衍射、高分辨扫描电镜、光吸收谱和荧光发光光谱等测试手段分析其性能,结果表明经过晶化处理可以在玻璃中长出CdS量子点,尺寸大约为10～25nm,吸收谱中出现明显的红移现象,反映出量子点的量子限域效应,荧光发光图谱中可以看出量子点发光主要由带隙发光和表面缺陷态发光组成,提高热处理温度可以改善晶粒的完整性.     

Effect of pyrolysis temperature on structural,microstructural and optical properties of nanocrystalline ZnO powders synthesised by ultrasonic spray pyrolysis technique

In this article, we report on the effect of pyrolysis temperature on structural, microstructural and optical properties of nanocrystalline ZnO powder synthesised by ultrasonic spray pyrolysis (USP) technique. Powder samples P1, P2 and P3 were prepared at various pyrolysis temperatures (temperature of 2nd zone) of 973, 1073 and 1273?K, respectively. Phases were identified and crystallite sizes were calculated from X-ray diffraction (XRD) diagrams. The morphology and size of ZnO nanocrystallites associated with nanopowder were studied using transmission electron micrograph (TEM). It revealed that the powder consisted of crystallites ranging in size from 9 to 20?nm. These values were matching with the crystallite sizes calculated from XRD. Both XRD and TEM studies of ZnO nanopowders showed that the crystallite sizes increased with an increase in the pyrolysis temperature. The synthesised nanopowders exhibited direct band gap (E _g) in the range 3.37–3.40?eV.     

Formation and optical properties of nanocrystalline selenium on Si substrate

We report on the formation of nanocrystalline selenium (NC-Se) on Si substrate by ultra-high vacuum physical deposition combined with rapid thermal annealing (RTA). NC-Se in a trigonal phase with an average diameter around 20 nm was formed during RTA on the amorphous selenium film at 180 °C. The NC-Se exhibits a broad and strong photoluminescence at ~ 1.7 eV at room temperature. Systematic optical investigations were carried out, and the emission was ascribed to the recombination between donor- and acceptor-like states at the NC-Se/a-Se interface.