Structural and optical properties of high quality ZnO thin film on Si with SiC buffer layer

ZnO thin films are grown on Si substrates with SiC buffer layer using ion plasma high frequency magnetron sputtering. These substrates are fabricated using a technique of solid phase epitaxy. With this technique SiC layer of thickness 20-200 nm had been grown on Si substrates consisting pores of sizes 0.5-5 μm at SiC and Si interface. Due to mismatching in lattice constants as well as thermal expansion coefficients, elastic stresses have been developed in ZnO film. Pores at the interface of SiC and Si are acting as the elastic stress reliever of the ZnO films making them strain free epitaxial. ZnO film grown on this especially fabricated Si substrate with SiC buffer layer exhibits excellent crystalline quality as characterized using X-ray diffraction. Surface topography of the film has been characterized using Atomic Force Microscopy as well as Scanning Electron Microscopy. Chemical compositions of the films have been analyzed using Energy Dispersive X-ray Spectroscopy. Optical properties of the films are investigated using Photoluminescence Spectroscopy which also shows good optical quality.     

Growth and characterisation of SiC films deposited on a-SiO2/Si (100) substrates

Abstract

The growth of polycrystalline SiC films has been carried out by low pressure chemical vapour deposition in a horizontal quartz reaction chamber using tetramethylsilane and H2 as the precursor gas mixture. Silicon (100) wafers were used as substrates. A thin Si O₂ amorphous layer of ~6 nm was formed before SiC deposition to reduce the strain induced by the 8% difference in thermal expansion coefficients between SiC and Si. Samples were. analysed by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and infrared reflectivity. The structure of films grown at temperatures between 950 and 1150°C varies from amorphous to polycrystalline SiC. Preferential [111] orientation and columnar growth of polycrystalline films develops with increasing temperature.

MST/3317     

Homoepitaxial 6H-SiC thin films by vapor-liquid-solid mechanism

Silicon carbide (SiC) is a IV-IV compound semiconductor with a wide energy band gap. Because of its outstanding properties, SiC can be used in high-power, high-temperature devices with high radiation resistance. In this study, a two-step vapor-liquid-solid (VLS) method was proposed for homoepitaxial growth of high quality 6H-SiC thin films, combining VLS growth and conventional chemical vapor deposition (CVD) processes. VLS growth was used to eliminate the micro-pipes (MPs) in the first step, and the subsequent step based on the CVD process was employed to improve the surface roughness. The morphology and structure of the as-grown thin films were investigated by scanning electron microscopy, X-ray energy dispersive spectroscopy, atomic force microscopy and high-resolution X-ray diffraction, showing that thin films grown by two-step method have good crystalline quality and small surface roughness.     

Heteroepitaxial Growth and Characterization of 3C-SiC Films on Si Substrates Using LPVCVD

3C-SiC films have been deposited on Si (111) substrates by the low-pressure vertical chemical vapor deposition (LPVCVD) with gas mixtures of SiH4, C3Hg and H2- The growth mechanism of SiC films can be obtained through the observations using field emission scanning electron microscope (FESEM). It is found that the growth process varies from surface control to diffusion control when the deposition temperature increases from 1270 to 1350℃. The X-ray diffraction (XRD) patterns show that the SiC films have good crystallinity and strong preferred orientation. The results of the high resolution transmission electron microscopy (HRTEM) image and the transmission electron diffraction (TED) pattern indicate a peculiar superlattice structure of the film. The values of the binding energy in the high resolution X-ray photoelectron spectra (XPS) further confirm the formation of SiC.     

体硅上外延超薄Si1-xGex用于制备SGOI材料

采用减压化学气相沉积的方法在Si衬底上制备了高质量的Si0.75Ge0.25/Si/Si0.86Ge0.14叠层材料,通过TEM、光学显微镜和XRD分析表明,外延的SiGe薄膜具有完好的晶格结构,平整的表面质量,SiGe薄膜处于完全应变状态.通过与Si上外延渐变缓冲层制备的SiGe材料比较发现,使用这种超薄的全应变Si...     

无压烧结合成纯Ti3SiC2及其晶体生长机理

在1400℃,用Ti,Si,C,Al,NaCl原料,氩气保护下无压烧结合成出纯净的、层状的Ti3SiC2陶瓷。用X射线衍射、扫描电子显微镜,透射电子显微镜对Ti3SiC2陶瓷的物相、表面形貌、微观结构进行表征。对合成出的Ti3SiC2陶瓷的微观形貌进行观察,发现Ti3SiC2晶体中有规整的六方形状的层状晶体,提出了Ti3SiC2晶体的自由生长的机理。Ti3SiC2晶体的生长机理由二维成核理论控制,台阶状晶体生长的形貌表明(002)晶面的生长要经过两个独立的过程。添加NaCl,有助于生成高纯度的层状Ti3SiC2陶瓷。     

Hetero-epitaxy and structure characterization of Si films on 6H-SiC substrates

In order to realize the non-ultraviolet application of SiC optoelectronic devices, Si/6H-SiC heterojunctions were prepared by the low-pressure chemical vapour deposition at 850 °C. The X-ray diffraction (XRD) and the selected area electron diffraction (SAED) results indicate that Si thin films have a monocrystalline structure and were grown along the (111) crystal plane. The rationality of the (111) growth plane was also analyzed by the theoretical calculation. High-density structural defects such as stacking faults and twins were observed on Si films by the high-resolution transmission electron microscopy. This phenomenon was also validated by the SAED patterns of defect-rich regions on Si films.     

Si(111)衬底上多层石墨烯薄膜的外延生长

利用固源分子束外延(SSMBE)技术, 在Si(111)衬底上沉积碳原子外延生长石墨烯薄膜, 通过反射式高能电子衍射(RHEED)、红外吸收谱(FTIR)、拉曼光谱(RAMAN)和X射线吸收精细结构谱(NEXAFS)等手段对不同衬底温度(400、600、700、800℃)生长的薄膜进行结构表征. RAMAN和NEXAFS结果表明: 在800℃下制备的薄膜具有石墨烯的特征, 而 400、600和700℃生长的样品为非晶或多晶碳薄膜. RHEED和FTIR结果表明, 沉积温度在600℃以下时C原子和衬底Si原子没有成键, 而衬底温度提升到700℃以上, 沉积的C原子会先和衬底Si原子反应形成SiC缓冲层, 且在800℃沉积时缓冲层质量较好. 因此在Si衬底上制备石墨烯薄膜需要较高的衬底温度和高质量的SiC缓冲层.     

Embedding of reduced pressure-chemical vapor deposition grown Ge nanocrystals in a high quality SiO2 matrix for non-volatile memory applications

We have obtained thanks to reduced pressure-chemical vapor deposition germanium nanocrystals in a high quality SiO₂ matrix. A perfect control of (i) the tunnel and control oxide layer thicknesses and (ii) the germanium nanocrystals' density and diameter has been achieved. Scanning electron microscopy was used to (i) determine the nucleation and growth rate of the germanium nanocrystals and (ii) evaluate their morphological stability during their embedding. We have also studied the influence of thin selectively grown Si films in order to passivate the surface of the germanium nanocrystals. X-ray photoelectron spectroscopy has shown that the germanium nanocrystals' surface properties are better with a Si capping. The polycrystalline state of the nanocrystals has been evaluated with X-ray diffraction. Transmission electron microscopy image reveals the lack of germanium diffusion and precipitation in the SiO₂ matrix.     

SAW器件用金刚石基c轴取向LiNbO3压电薄膜的制备

采用脉冲激光沉积技术,在以c轴取向ZnO作为缓冲层的金刚石/硅基底上制备出了结晶良好的高c轴取向LiNbO3薄膜。利用X射线衍射对薄膜的结晶质量和c轴取向性进行了研究,结果表明制得的LiNbO3薄膜具有高度c轴取向且结晶质量良好。采用扫描电子显微镜和原子力显微镜对薄膜的表面形貌进行了分析,发现薄膜表面光滑,晶粒尺寸均匀,薄膜表面粗糙度约为20nm。     

Preparation of Zr-Si thin films by a simultaneous deposition and reaction process using pulsed ion beams

Thin films of Zr were deposited on Si single crystal substrates by a simultaneous deposition and reaction (SDR) process using pulsed ion beams. The thin films were characterized by X-ray diffraction, selected area electron diffraction, scanning electron microscopy and transmission electron microscopy. One of the thin films with a wavy surface contained not only Zr grains but also polycrystalline ZrSi₂ and Si grains. From the results, the mechanism of the SDR process was explained as follows. First, Zr plasma, which had been formed from the ion-beam irradiated Zr target, was applied on a single crystal Si substrate to fuse a part of the single crystal Si substrate. Then, the fused Si layer enhanced the reaction with deposited Zr atoms. The present investigation implied a possibility of formation of thick reaction layers between thin films and substrates to improve the adhesion and the electrical properties.     

Surface nano-structured silicon carbide thin film produced using hot filament decomposition of ethylene at low temperature on silicon wafer

The structure and spectroscopic properties of nano-structured silicon carbide (SiC) thin films were studied for films obtained through deposition of decomposed ethylene (C₂H₄) on silicon wafers via hot filament chemical vapor deposition method at low temperature followed by annealing at various temperatures in the range 300-700 °C. The prepared films were analyzed with focus on the early deposition stage and the initial growth layers. The analysis of the film's physics and structural characteristics was performed with Fourier transform infrared spectroscopy and Raman spectroscopy, scanning electron microscopy with energy dispersive X-ray spectroscopy, and X-ray diffraction. The conditions for forming thin layer of cubic SiC phase (3C-SiC) are found. X-ray diffraction and Raman spectroscopy confirmed the presence of 3C-SiC phase in the sample. The formation conditions and structure of intermediate SiC layer, which reduces the crystal lattice mismatch between Si and diamond, are essential for the alignment of diamond growth. This finding provides an easy way of forming SiC intermediate layer using the Si from the substrate.     

Characterization of crystalline structure and morphology of NiO thin films

We investigated the relation of sputtering powers with structural and morphological properties of nickel oxide (NiO) thin films. NiO thin films were fabricated by using an rf-reactive sputtering method on Si(100) substrates with a Ni target in a partial pressure of oxygen and argon. The films were deposited by various rf-sputtering powers from 100 to 200 W at room temperature. The phases and crystalline structures of the deposited films were investigated by using grazing incident X-ray diffraction (XRD). The thickness and surface morphology of the films were investigated by using a field emission-scanning electron microscopy (FE-SEM). The different sputtering conditions drastically affected the crystallinity and the surface morphology of NiO thin films. A combined analysis of the data obtained from X-ray diffraction and SEM images demonstrates that the preferred orientation of NiO films tends to grow from (111) to (200) direction as increasing the sputtering power, which can be explained by in terms of the surface energy along the indexing plane in an fcc structure. As increasing the rf power, lattice constants decreased from 4.26 to 4.20 angstroms and samples became high-quality crystals. Under our experimental condition, NiO films prepared at 150 W with 20% partial pressure of oxygen and 7 cm distance from the sample to the target show the best quality of the crystal.     

High concentration erbium doping of silicon-rich SiO2 thin films on silicon

In this work, high concentration erbium doping in silicon-rich SiO₂ thin films is demonstrated. Si plus Er dual-implanted thermal SiO₂ thin films on Si substrates have been fabricated by using a new method, the metal vapor vacuum arc ion source implantation with relatively low ion energy, strong flux and very high dose. X-Ray photoelectron spectroscopy measurement shows that very high Er concentrations on the surfaces of the samples, corresponding to 10 at.% or the doping level of 10²¹ atoms cm⁻³, are achieved. This value is much higher than that obtained by using other fabrication methods such as the high-energy ion implantation and molecular beam epitaxy. Reflective high-energy electron diffraction, atomic force microscopy and cross-section high-resolution transmission electron microscopy observations show that the excess Si atoms in SiO₂ matrix accumulate to form Si clusters and then crystallize gradually into Si nanoparticles embedded in SiO₂ films during dual-ion implantation followed by rapid thermal annealing. Er segregation and precipitates are not formed. Photoluminescence at the wavelength of 1.54 μm exhibits very weak temperature dependence due to the introduction of Si nanocrystals into the SiO₂ matrix. The 1.54-μm light emission signals from annealed samples decrease by less than a factor of 2 when the measuring temperature increases from 77 K to room temperature.     

喷雾热分解法制备MgO薄膜的研究

用简单的压缩空报喷雾热分法以醋酸镁为原料在Ｓｉ（１００）衬底上成功地制备了（１００）取向的ＭｇＯ薄膜。结果表明,为获得（１００）取向的ＭｇＯ薄膜,衬底温度和喷雾速率是关键因素。控制实验条件,在６００℃得到了（１００）取向的ＭｇＯ薄膜。同时,用Ｘ射线衍射（ＸＲＤ）、原子力显微镜（ＡＦＭ）和透射电镜（ＴＥＭ）对薄膜的微观结构进行了分析。     

Si-rich a-SiC:H thin films: Structural and optical transformations during thermal annealing

Amorphous hydrogenated silicon-rich silicon carbide (a-Si_0.8C_0.2:H) thin films were prepared by plasma enhanced chemical vapour deposition and were thermally annealed in a conventional resistance heated furnace at annealing temperatures up to 1100 °C. The annealing temperatures were varied and the samples were characterised with Auger electron spectroscopy, glancing incidence X-ray diffraction, Raman spectroscopy, Fourier transformed infrared spectroscopy, transmission electron microscopy and photoluminescence (PL) spectroscopy. As-deposited a-Si_0.8C_0.2:H thin films contain a large amount of hydrogen and are amorphous. When annealing the films, the onset of Si crystallisation appears at 700 °C. For higher annealing temperatures, we observed SiC crystallites in addition to the Si nanocrystals (NCs). The crystallisation of SiC correlates with the occurrence of a strong PL band, which is strongly reduced after hydrogen passivation. Thus PL signal originates from the SiC matrix. Si NCs exhibit no PL yield due to their inhomogeneous size distribution.     

A photochemical method for the preparation of indium oxide and indium-cobalt oxides thin films

Indium oxide and indium-cobalt oxide thin films have been successfully prepared by direct UV irradiation of amorphous films of β-diketonate complexes on Si(1 0 0) substrates. Deposited films were characterized by X-ray diffraction, Auger electron spectroscopy and X-ray photoelectron spectroscopy. The surface morphology of the films, examined by atomic force microscopy and scanning electron microscopy, revealed that mixed indium-cobalt oxide films are much smoother than In₂O₃ films, with rms surface roughness of 7.24 and 26.1 nm, respectively.     

Vacuum-deposited carbon coatings

In recent years, highly favorable results have been obtained using low temperature isotropic pyrolytic carbons in prosthetic devices requiring a high degree of thromboresistance. The development of vacuum-deposited carbon coatings was undertaken to extend the application of carbon to geometries and configurations that cannot be fabricated from low temperature isotropic carbon. Vacuum-deposited coatings have been produced on a variety of metallic and polymeric substrates.The different vacuum deposition processes which have been investigated include electron beam gun evaporation using high vacuum, gas scattering and ion- plating conditions. In addition, sputtering processes using ion beams and magnetically confined plasmas were studied.The surface morphology, structure and preferred orientation of the coatings produced by the different processes were characterized by scanning and transmission electron microscopy. Film purity and interfacial characteristics were examined by Auger electron spectroscopy.The scanning electron microscopy study shows that thin carbon films generally have a smooth and featureless surface morphology. However, other surface morphology features are obtained in thicker films, depending on the processing conditions. The transmission electron micrographs show the absence of structure and growth features. Electron diffraction indicates that the films consist of a turbostratic phase and a non-crystalline phase. The apparent crystallite sizes are small, and there is no three-dimensional ordering. Generally, the films are isotropic and consist of relatively pure carbon, with the degree of disorder dependent on the process conditions.     

Nanostructured organic-inorganic photodiodes with high rectification ratio

High quality organic-inorganic heterojunction photodiodes based on nanostructured copper (II) phthalocyanine (CuPc) and intrinsic zinc oxide (i-ZnO) have been fabricated. The i-ZnO thin films/layers were grown by RF magnetron sputtering on clean indium tin oxide (ITO) coated glass substrates. These films have been characterized by optical absorption and field emission scanning electron microscopy (FESEM). CuPc thin films deposited at room temperature on i-ZnO have exhibited a change in their surface morphology with the post-deposition annealing temperature under normal atmosphere. The electrical dark conductivity and the photoconductivity of ITO/i-ZnO/CuPc/Au sandwich structures have been measured under various photoexcitation intensities using a xenon light source. The devices have shown excellent reproducibility of their electrical characteristics and high rectification ratios. The highest rectification ratio is nearly 831 calculated above the threshold voltage at room temperature for the sample annealed at 250?°C (i.e.?Pc 250). The effects of the annealing temperature of CuPc on the surface morphology, rectification ratio, and optical properties have been discussed.     

Annealing effect on the photoluminescence of Si nanocrystallites thin films

Si nanocrystallites thin films on p-type (100) Si substrate have been fabricated by pulsed laser deposition (PLD) using a Nd:YAG laser.After deposition, samples were annealed in several environmental gases at the temperature range from 400 to 800 °C. Strong violet-indigo photoluminescence has been observed at room temperature (RT) from nitrogen ambient-annealed Si nanocrystallites. The variation of photoluminescence (PL) properties of Si nanocrystallites thin films has been investigated depending on annealing temperatures. As the results of PL and high-resolution transmission electron microscope (HRTEM) measurements, we could suggest that the origin of violet-indigo PL from the films was related to the quantum size effect of Si nanocrystallites.