Structural,compositional and electrical characterization of Si-rich SiOx layers suitable for application in light sensors

Metal-Oxide-Silicon (MOS) structures containing silicon nanoparticles (SiNPs) in three different gate dielectrics, single SiO_x layer (c-Si/SiNPs-SiO_x), two-region (c-Si/thermal SiO_x/SiNPs-SiO_x) or three-region (c-Si/thermal SiO₂/SiNPs-SiO_x/SiO₂) oxides, were prepared on n-type (100) c-Si wafers. The silicon nanoparticles were grown by a high temperature furnace annealing of sub-stoichiometric SiO_x films (x=1.15) prepared by thermal vacuum evaporation technique. Annealing in N₂ at 700 or 1000 °C leads to formation of amorphous or crystalline SiNPs in a SiO_x amorphous matrix with x=1.8 or 2.0, respectively. The three-region gate dielectric (thermal SiO₂/SiNPs-SiO₂/SiO₂) was prepared by a two-step annealing of c-Si/thermal SiO₂/SiO_x structures at 1000 °C . The first annealing step was carried out in an oxidizing atmosphere while the second one was performed in N₂. Cross-sectional Transmission Electron Microscopy and X-ray Photoelectron Spectroscopy have proven both the nanoparticle growth and the formation of a three region gate dielectric. Annealed MOS structures with semitransparent aluminum top electrodes were characterized electrically by current/capacitance–voltage measurements in dark and under light illumination. A strong variation of the current at negative gate voltages on the light intensity has been observed in the control and annealed at 700 °C c-Si/SiNPs-SiO_x/Al structures. The obtained results indicate that MOS structures with SiO_1.15 gate dielectric have potential for application in light sensors in the NIR–Visible Light–UV range.     

One step synthesis of ZnO nanoparticles in free organic medium: Structural and optical characterizations

Nano-sized ZnO particles are synthesized by the sol–gel method in aqueous medium without any annealing, ripening treatment or organic additive addition. The structure, morphology, and optical properties of these ZnO nanoparticles are characterized by X-ray Diffraction (XRD), Transmission Electron Microscopy (TEM) and Ultraviolet–visible spectroscopy (UV–vis) respectively. The effect of the synthesis temperature on the morphological (shape and size) and optical properties of these nanoparticles have been examined for temperatures varying from 0 to 80 °C. XRD analysis shows that the as-prepared particles crystallize in the Würtzite hexagonal phase even at very low synthesis temperatures. Meanwhile, Transmission Electron Microscopy observations reveal that the particles present a significant change in shape and size as the temperature increases. They take a flower shape, at very low temperatures, a conical or ellipsoidal shape when the temperature is ranging from 20 °C to 50 °C and a rodlike shape with a hexagonal section at elevated temperatures (>50 °C). Moreover, it has been observed that the increasing of the synthesis temperature leads to a net increase in the average particle size. It affects especially the length in the minor axis direction while the length in the major direction (c-axis) remains nearly constant. Optical properties, carried out by spectrophotometric measurements, indicate that increasing the temperature results in lower band gap energy values.     

Mg预处理蓝宝石衬底法制备的Zn极性ZnO外延薄膜的结构研究

通过分子束外延法在经Mg预处理的蓝宝石衬底上制备了ZnO单晶薄膜,利用高分辨透射电镜、电子全息和X射线能谱对该薄膜的结构进行了细致的研究.结果表明,在蓝宝石衬底上预沉积一层很薄的Mg层,可以生长均匀Zn极性的ZnO外延薄膜.ZnO/MgO/蓝宝石的界面非常清晰锐利,同时在界面处可以观察到大约3个原子层的MgO.预沉积的Mg薄层对随后ZnO的极性选择起了关键性作用.     

中红外区基质折射率对碳化硅颗粒散射强度的影响

基于Mie散射理论,对不同基质中的碳化硅材料散射强度进行数值计算与理论分析,得到了中红外波段反常色散区和正常色散区中散射强度的分布特征,揭示了入射波长、基质折射率与散射强度分布的内在规律。研究结果为该材料在中红外区的开发和应用提供了理论依据。     

Ag-石墨烯纳米复合材料的室温制备及其结构分析

在室温条件下利用水合肼将氧化石墨烯和AgNO3还原获得Ag-石墨烯纳米复合材料,并利用X射线光电子能谱(XPS),X射线衍射(XRD),X射线能谱(EDX)及高分辨透射电镜(HRTEM)等方法对制备的纳米复合材料进行分析.结果表明:Ag-石墨烯复合材料中石墨烯的含氧官能团数量大幅降低,氧化石墨烯已被还原为石墨烯;Ag纳...     

Nondestructive defect characterization of SiC substrates and epilayers

This study presents a nondestructive and in-depth defect characterization method, based on the principle of polarized light microscopy (PLM), which can be used to quickly evaluate SiC substrates and epilayers. The developed PLM system has the capability to map, on a wafer scale, micropipes, elementary screw dislocations, and domain boundaries in SiC wafers. One unique feature of the PLM system is the ability to characterize the wafer with and without an epilayer, providing a newly found opportunity to investigate threading defect propagation in the overgrown epilayer. The correlation between SiC substrate defects and epilayer defects will be established.     

Influence of boron doping on the properties of amorphous and microcrystalline SiC films prepared using ECR-CVD

Hydrogenated silicon carbide films (SiC:H) were deposited using the electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD) method from a mixture of methane, silane, and hydrogen, with diborane as the doping gas. The effect of changes in the percentage of the diborane to reactant gas mixture on the deposition rate, optical bandgap, and photoconductivity were investigated. There is evidence from Raman scattering analysis to show that films deposited at a low microwave power of 150 W were all amorphous and the bandgap decreases as the diborane level is increased whereas films deposited at a high microwave power of 800 W at low diborane levels are highly photoconductive and contain microcrystalline silicon inclusions. These films become amorphous as the diborane level is increased, while the optical bandgap remains relatively unaffected throughout the entire range of diborane levels investigated. The effect of the microwave power was also investigated. The conductivity increases rapidly to a maximum, followed by rapid reduction at high microwave powers. Raman scattering analysis showed evidence of the formation and increase of microcrystalline silicon inclusions and diamond-like components in the films, the former of which could account for the rapid increase and the latter the subsequent decrease in the conductivity.     

Investigation of structural,optical and morphological properties of copper doped zinc sulphide nanoparticles

Semiconductor nanoparticles doped with transition metal ions can influence the transition probabilities and electronic structure. The undoped and copper doped zinc sulphide nanoparticles with various concentrations are synthesized by wet chemical co-precipitation method. These nanoparticles are characterized by using X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED), UV–visible (UV–vis) absorption spectroscopy, Fourier Transform Infrared (FT-IR) Spectroscopy, conductivity measurement and time-resolved photoluminescence studies. X-ray powder diffraction analysis reveals that the synthesized samples have cubic zinc blende structure. The Scanning Electron Microscope shows the synthesized nanoparticles are agglomerated. The UV–visible spectra reveal the absorption edge is red shifted. The FT-IR spectra show vibrational peaks around 617 cm⁻¹ which indicate the presence of Cu–S stretching modes. The AC conductivity measurement confirms the semiconducting nature and shows a marked increase in conductivity as the doping concentration of copper increases. The photoluminescence shows that the emission at 426 nm may be due to transition from the conduction band to the zinc vacancies. These transition metal ions doped semiconductor nanoparticles have important applications in solid state lighting, imaging, and other photonic devices.     

Boron implantation and epitaxial regrowth studies of 6H SiC

Implantation of B has been performed into an epitaxially grown layer of 6H SiC, at two different B concentrations, 2×10¹⁶ cm⁻³ and 2×10¹⁸ cm⁻³. Subsequently, an epitaxial layer was regrown on the B implanted layer. The samples were investigated by transmission electron microscopy (TEM) and secondary ion mass spectrometry (SIMS). In the highly B-doped layers plate-like defects were found, associated with large strain fields, and an increased B concentration. These defects were stable at the originally implanted region during regrowth and at anneal temperatures up to 1700°C. In the samples implanted with the lower B concentration, no crystal defects could be detected by TEM. No threading dislocations or other defects were observed in the regrown epitaxial layer, which shows the possibility to grow a layer with high crystalline quality on B implanted 6H SiC. By SIMS, it was found that B piles up at the interface to the regrown layer, which could be explained by enhanced diffusion from an increased concentration of point defects created by implantation damage in the region. B is also spread out into the original crystal and in the regrown layer at a concentration of below 2×10¹⁶ cm⁻³, with a diffusion constant estimated to 1.3×10⁻¹² cm²s⁻¹. This diffusion is most probably not driven by implantation damage, but by intrinsic defects in the grown crystal. Our investigation shows that the combination of implantation and subsequent regrowth techniques could be used in SiC for building advanced device structures, with the crystal quality in the regrown layer not being deteriorated by crystal defects in the implanted region. A device process using B implantation and subsequent regrowth could on the other hand be limited by the diffusion of B.     

Growth and characterization of GaN thin films on SiC SOI substrates

SiC semiconductor-on-insulator (SOI) structures have been investigated as substrates for the growth of GaN films. The SiC SOI was obtained through the conversion of Si SOI wafers by reaction with propane and H₂. (111) SiC SOI have been produced by this carbonization process at temperatures ranging from 1200 to 1300°C. X-ray diffraction (XRD) and infrared spectroscopy (FTIR) are used to chart the conversion of the Si layer to SiC. Under our conditions, growth time of 3 min at 1250°C is sufficient to completely convert a 1000? layer. XRD of the SiC SOI reveals a single SiC peak at 2θ = 35.7° corresponding to the (111) reflection, with a corrected full width at half-maximum (FWHM) of ~590±90 arc-sec. Infrared spectroscopy of SiC SOI structures obtained under optimum carboniza-tion conditions exhibited a sharp absorption peak produced by the Si-C bond at 795 cm⁻¹, with FWHM of ∼ 20–25 cm⁻¹. Metalorganic CVD growth of GaN on the (111) SiC SOI was carried out with trimethylgallium and NH₃. The growth of a thin (≤200?), low temperature (500°C) GaN buffer layer was followed by the growth of a thick (∼2 μm) layer at 1050°C. Optimum surface morphology was obtained for zero buffer layer. XRD indicates highly oriented hexagonal GaN, with FWHM of the (0002) peak of ~360±90 arc-sec. Under high power excitation, the 300°K photoluminescence (PL) spectrum of GaN films exhibits a strong near band-edge peak (at λ_p~371 nm, with FWHM = 100–150 meV) and very weak yellow emission. Under low power excitation, the 370 nm PL emission from the GaN/SiC SOI structure increases rapidly with SiC carbonization temperature, while the yellow band (∼550–620 nm) correspondingly decreases.     

Synthesis and characterization of Manganese doped Tungsten oxide by Microwave irradiation method

The aim of this article is to synthesis tungsten oxide (WO₃) nanoparticle along with Manganese (3 wt% and 10 wt%) by Microwave irradiation method. The physical properties of the synthesized Manganese doped Tungsten oxide materials were characterized by X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscope (TEM), UV-Diffuse Reflectance Spectroscopy, SEM-EDAX and Photoluminescence studies. The predominant peaks obtained in X-ray diffraction pattern reveal the crystalline nature of the nanoparticles and the structure belongs to Monoclinic for pure and Mn doped WO₃. FTIR analysis shows the presence of Tungsten and oxygen in the synthesis material and verified with EDAX. TEM analysis shows both pristine and Mn doped WO₃ nanopaticles. They are having spherical shaped morphology with average particle size from 35 to 40 nm. UV-DRS revealed that the bandgap energy for pure and Manganese doped WO₃ are discussed in this article. The Scanning Electron Microscope analysis shows the plate like morphology for pure WO₃ and the morphology were decreased by doping Manganese. The defects and oxygen deficiencies were analysed by photoluminescence spectroscopy.     

Investigation on the Luminescent Properties of SiC

Silicon carbide (SiC) is an excellent microelectronic material used to fabricate high frequency, high temperature, high power and non--volatile memory devices. But due to its indirect band gap, SiC based LED can‘t emit light so efficiently as GaN based LED, so people are eager to seek effective means to improve its luminescence efficiency. Amorphous SiC, porous crystalline SiC, nanometer SiC produced by CVD methods and porous SiC formed by ion implantation are investigated, and great progresses have been gained during the latest few years, which make SiC a promising material for developing OEIC.     

CdS纳米粒子的合成方法

在十二烷基硫酸钠的水溶液中,以Cd(NO3)2和TAA为源材料,通过微波辐射加热合成了立方晶相CdS半导体纳米粒子,并用XRD、TEM、紫外反射光谱及荧光光谱进行了表征。     

Structural characterization and properties of nano-sized Cd1−xCoxO dilute magnetic semiconductors prepared by solvothermal method

Nanoparticles of Co-doped CdO with 4.2, 9.3, and 15.4 weight% were successfully synthesized by a modified solvothermal method through oxalate precursor route. The oxalate served as an excellent precursor for the synthesis of pure and homogeneous oxide nanoparticles. Powder X-ray diffraction studies revealed the monophasic nature of these nanoparticles. The lattice parameter decreased monotonically with increasing Co concentration, confirming Co was doped into the CdO host lattice. Particle size decreased and surface area increased on increasing the dopant ion concentration. Optical absorption measurements showed an energy band gap that increased with Co concentration. Magnetization studies indicated that the samples showed paramagnetic behavior with weak antiferromagnetic interactions.     

碳化硅CMOS反相器的特性

建立了6 H- Si C CMOS反相器的电路结构和物理模型,并利用MEDICI软件对其特性进行了模拟.研究了Si C CMOS反相器的温度特性,结果表明,室温下沟道长度为1.5 μm的6 H- Si C CMOS反相器的阈值电压、高电平噪声容限和低电平噪声容限分别为1.6 5 7,3.15 6和1.4 70 V,且随着温度的升高而减小.     

Synthesis,characterization and in vitro cytotoxicity study of calcium ferrite nanoparticles

In the present paper, calcium ferrite nanoparticles have been synthesized by the sol–gel method. The orthorhombic structure of calcium ferrite nanoparticles has been revealed by X-ray diffractometry. The morphology and size (5–10 nm) of the synthesized nanoparticles have been observed by scanning electron microscopy and transmission electron microscopy, respectively. Fourier transform infrared spectroscopy and thermogravimetric analysis have been studied, in order to ensure absence of impurities. The magnetic analysis has been studied by vibrating sample magnetometer, where the superparamagnetic behavior with saturation magnetization of 36.4 emu/g was observed. In vitro cytotoxicity test on T cell lines (Jurkat cells) using MTT (3-(4, 5-Dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide, a tetrazole) assay revealed the biocompatibility of the synthesized calcium ferrite nanoparticles at particle concentration below 250 µg/ml.     

小角衍射法精确测定Mo/Si软X射线多层膜的结构

通过对周期性Mo/Si多层膜Cu靶K_(?)线小角衍射曲线的分析,并进一步采用对局部曲线进行分步数值拟合的方法,确定了多层膜的结构参数及界面质量。估算了多层膜样品在λ=20nm附近的正入射反射率接近10％。     

碳化硅材料发光特性研究进展

碳化硅作为一种优秀的微电子材料,在高频、高温、大功率、强辐射环境中颇具应用潜力。然而由于其间接带隙的特点,碳化硅LED不能像氮化镓、磷化镓LED那样有效发光,因此人们竞相研究能提高碳化硅发光效率的方法,其中包括非晶碳化硅、多孔单晶碳化硅、用CVD方法制备的纳米碳化硅和用离子注入方法制备的多孔碳化硅。在最近几年,这些研究已取得巨大进展,从而使其成为适用于发展中的OEIC技术的颇具潜力的材料。     

具有温度稳定性的SiC CMOS运算放大器的设计

设计了具有温度稳定性的SiC CMOS运算放大器.根据所希望的IDSat(ZTC)和任一节点泄漏电流为零的原则设计偏置电路;输入采用差分输入,同时按照泄漏电流匹配的原则,合理选取Dcomp的面积.Si MOS器件电源电压为5 V,采用TSMC 0.25 μm工艺制作.当温度从300 K变化到600 K时,SiC 运放的增益和相位裕度的变化率分别为2.5%和3.3%,而Si电路的增益从300 K的64 dB降到-80 dB,失去电路的稳定性.但是,由于SiC MOS器件沟道迁移率低,导致器件的跨导低于相同尺寸下的Si器件,所以其开环增益也小于相同结构和尺寸的Si运算放大器.