A new CVD reactor for semiconductor film deposition

The concept and design of a new chemical vapor deposition (CVD) reactor is presented for both epitaxial and nonepitaxial film deposition in semiconductor processing. The reactor is designed in such a way that a stagnant semiconductor source fluid of uniform concentration is provided for the film deposition without causing free or forced convection. The supply of the source gas for the deposition is by diffusion through a porous material such as quartz or graphite. Compared to the low pressure CVD (LPCVD) reactor with mounted wafer configuration, the new reactor should give a better film thickness uniformity and about an order of magnitude reduction in the amount of the source gas required. Further, at least for polycrystalline silicon deposition, the deposition rate can be much higher than is currently practiced with the LPCVD reactor. Design equations for the reactor are given. Details on the design for the polycrystalline silicon deposition are also given.     

等离子体增强化学气相沉积技术制备锗反蛋白石三维光子晶体

采用溶剂蒸发对流自组装法将单分散二氧化硅(SiO2)微球组装形成三维有序胶体晶体模板,以锗烷(GeH4)为先驱体气用等离子增强化学气相沉积法在350℃填充高折射率材料锗.获得了锗反蛋白石光子晶体.通过扫描电镜、X射线衍射仪对锗反蛋白石的形貌、成分、结构进行了表征.结果表明:锗在SiO2微球空隙内填充均匀,得到的锗为多晶态.锗反蛋白石光子晶体为三维有序多孔结构.等离子体增强化学气相沉积的潜在优势在于可实现材料的低温填充,从而以高分子材料为模板进行复型,得到多种结构的三维光子晶体.     

Room-temperature efficient light detection by amorphous Ge quantum wells

In this work, ultrathin amorphous Ge films (2 to 30 nm in thickness) embedded in SiO₂ layers were grown by magnetron sputtering and employed as proficient light sensitizer in photodetector devices. A noteworthy modification of the visible photon absorption is evidenced due to quantum confinement effects which cause both a blueshift (from 0.8 to 1.8 eV) in the bandgap and an enhancement (up to three times) in the optical oscillator strength of confined carriers. The reported quantum confinement effects have been exploited to enhance light detection by Ge quantum wells, as demonstrated by photodetectors with an internal quantum efficiency of 70%.     

Anodic formation of binary and ternary compound semiconductor films for photovoltaic cells

By anodic oxidation of copper sheets in sulfide anion-containing electrolytes copper chalcogenide semiconductor films suitable for photovoltaic applications can be attained. Anodically chalcopyrite (Cu2S) has been formed as pure, mechanically stable, homogeneous and adhesive polycrystalline films, consisting of well-developed large crystallites. Cu2S coated copper sheets were produced with an area of 3cm*3cm. P-n-junctions formed by evaporation of CdS onto the anodically formed Cu2S films show an energy efficiency of 3.3. The extension of this process to ternary systems, like copper/indium/sulfur, is likely to be possible. A mixture of Cu2S and CuInS2 could be formed by codepositing In2S3 together with Cu2S. Cu2Se-films with a thickness of up to 1 mum were formed by chemical bath deposition.     

Single-crystal diamond microneedles shaped at growth stage

Single-crystal diamond microneedles were extracted from (001) textured polycrystalline films. The films were produced using a plasma enhanced chemical vapor deposition (CVD) from a CH₄/H₂ gas mixture activated by a direct current discharge. The as-grown textured polycrystalline CVD films consist of pyramid-shaped micrometer size diamond crystallites embedded into a nanodiamond ballas-like material. The less ordered fraction of the CVD film material was removed selectively using thermal oxidation. A dependence of the diamond needle shape on the CVD and the oxidation process parameters was revealed via a computer simulation and experimental studies. Ability for mass production of the diamond microneedles of different shapes was demonstrated. The needles are suitable for various applications from microcutting tools to quantum information processing.     

Chemical bath deposition of h-MoO3 on optical fibre as room-temperature ammonia gas sensor

This study successfully developed a semiconductor metal oxide-based ammonia gas sensor that was powered by an Ultraviolet–Visible-near-IR optical light source. However, optical fibre gas sensors using single metal oxide nanomaterial are limited. To address this situation, a h-MoO₃ nanorod was grown on a tapered region of optical fibre glass using a simple chemical bath deposition to form a unique sensing element. An additional annealing treatment was then performed to modify the oxidation state of h-MoO₃. The property changes of the samples were characterised using different techniques, such as FESEM, TEM, XRD, XPS, TGA and UV–Vis. Overall, the annealing treatment improved the sensitivity performance, response and recovery time of the sensor towards NH₃. h-MoO₃ that was annealed at 150 °C in air showed stable room temperature absorbance responses of 0.05, 0.18, 0.22, 0.28 and 0.35, a fast response time of 210 s towards 500 ppm of NH₃ and strong stability and repeatability. The optical NH₃ gas-sensing behaviour was significantly correlated with the non-stoichiometric Mo⁵⁺ content. The chemisorbed oxygen species and physiosorbed NH₃ altered the refractive index and its absorption coefficient on the nanorod, which manipulated the optical signal and acts as a sensing mechanism. These results verify that a chemical bath deposition growth of the h-MoO₃ nanorod exhibits a promising optical sensing characteristic, which paves a path for emerging gas-sensing technology.     

Preparation of silica glass doped with nitrogen by modified chemical vapor deposition

A thermodynamic analysis of the doping of silica glass with nitrogen by the chemical vapor deposition methods has been carried out. The fundamental differences are revealed between the plasma chemical vapor deposition and modified chemical vapor deposition methods. The basic parameters of nitrogen introduction into silica glass are determined by thermodynamic calculations. It is found that the main factor that ensures doping of silica glass with nitrogen by the modified chemical vapor deposition is an extremely low partial oxygen pressure in the reaction zone. The results of theoretical analysis are used in practice for nitrogenizing silica glass by modified chemical vapor deposition. The increment in the refractive index is equal to 0.0015.     

Preparation of silica glass doped with nitrogen by modified chemical vapor deposition

A thermodynamic analysis of the doping of silica glass with nitrogen by the chemical vapor deposition methods has been carried out. The fundamental differences are revealed between the plasma chemical vapor deposition and modified chemical vapor deposition methods. The basic parameters of nitrogen introduction into silica glass are determined by thermodynamic calculations. It is found that the main factor that ensures doping of silica glass with nitrogen by the modified chemical vapor deposition is an extremely low partial oxygen pressure in the reaction zone. The results of theoretical analysis are used in practice for nitrogenizing silica glass by modified chemical vapor deposition. The increment in the refractive index is equal to 0.0015.     

N,N−二甲基−二硫代甲酰胺丙磺酸钠对THPED体系化学镀铜的影响

研究了N,N?二甲基?二硫代甲酰胺丙磺酸钠(DPS)作为添加剂对以四羟丙基乙二胺(THPED)为单一配位剂的化学镀铜体系的沉积速率、镀层形貌和晶体结构的影响。结果发现,当DPS的质量浓度从0 mg/L增大到1.0 mg/L时,沉积速率从2.91μm/h提高到6.73μm/h,所得镀层结晶均匀、细致。线性扫描伏安测量结果表明,DPS是通过促进甲醛的阳极氧化来加速化学镀过程。本体系的Cu镀层主要呈面心立方多晶取向,DPS的添加会令晶面取向从(220)转变为(111)。     

Influences of Mn doping on the microstructural,semiconducting, and optoelectronic properties of HgO nanostructure films

Mn-doped HgO nanostructured thin films (Hg_1-xMn_xO) have been prepared using electron beam evaporation technique on Corning glass (1022) substrate at room temperature with different concentrations x = 0, 0.015, 0.05, 0.1, 0.15, and 0.2. The microstructural, morphological, semiconducting, and optoelectronic properties of the films have been investigated. The X-ray diffraction spectra suggest a hexagonal wurtzite type structure with lattice parameters decreased with increasing Mn content. It was found that the average particle size of the films decreases with increasing Mn doping which is confirmed by FE-SEM and AFM micrographs. The optical band gap of the investigated Mn-doped HgO nanocrystalline films is determined from the absorption coefficient and found to increase with the increase of Mn concentration which is attributed to the sp-d exchange interaction and/or the quantum confinement effect. The refractive index and extinction coefficient of the Mn-doped HgO films are also reported. The refractive index dispersion n(λ) is analyzed by single-effective-oscillator dispersion model proposed by the Wemple–DiDomenico (WDD). The oscillator parameters were estimated. The obtained dispersion values are suitable for the design of optoelectronic devices.     

碱性品红光敏感的新型光致聚合物全息存储材料

本文制备了一种以碱性品红为光敏剂的新型全息存储材料,且使用波长为532nm的半导体激光器成功研究了材料的全息特性。研究表明,该材料具有较高的衍射效率、曝光灵敏度和较大的折射率调制度,衍射效率近40%,灵敏度为8.38×10-4cm2/mJ,折射率调制度为4.5×10-4。在存储介质膜中存储了全息图像,再现图像较为清晰,对比度与保真度较为理想,说明该材料具有较好的全息存储性能,适合作为高密度全息存储介质。     

Electronic Structure of a Hydrogenic Acceptor Impurity in Semiconductor Nano-structures

The electronic structure and binding energy of a hydrogenic acceptor impurity in 2, 1, and 0-dimensional semiconductor nano-structures (i.e. quantum well (QW), quantum well wire (QWW), and quantum dot (QD)) are studied in the framework of effective-mass envelope-function theory. The results show that (1) the energy levels monotonically decrease as the quantum confinement sizes increase; (2) the impurity energy levels decrease more slowly for QWWs and QDs as their sizes increase than for QWs; (3) the changes of the acceptor binding energies are very complex as the quantum confinement size increases; (4) the binding energies monotonically decrease as the acceptor moves away from the nano-structures’ center; (5) as the symmetry decreases, the degeneracy is lifted, and the first binding energy level in the QD splits into two branches. Our calculated results are useful for the application of semiconductor nano-structures in electronic and photoelectric devices.     

CVD diamond optics for ultraviolet

The optical properties of CVD polycrystalline diamond have been studied in order to evaluate the feasibility of diamond mirrors operating in the UV spectral region. Diamond is a very attractive material for space application, since it offers a unique combination of high UV reflectivity, low reflectivity and high transmittance in the visible, mechanical hardness and chemical inertness. In addition, diamond has a high thermal conductivity, which should stabilize the refractive index. The UV reflectance at normal incidence and at 45°, the polarization degree and the transmittance in the visible of some CVD diamond samples have been measured. Opaque and transparent highly polished diamonds have been tested in order to evaluate the contribution of non-diamond carbon to the reflectance. The results have also been compared to the reflectance curves obtained using a high-pressure high-temperature (HPHT) single-crystal diamond to evaluate the influence of scattering from the polished surface of the CVD diamond layers.     

用离子束辅助沉积技术制备ZnS/MgF2膜

研究了用离子束辅助沉积技术在玻璃面交替镀覆高折射率和低折射率膜,从冷光灯大量生产的需要出发,对离子源的结构以及镀膜系统作了改进。     

Deposition and characterization of nanocrystalline and amorphous Ni–W coatings with embedded alumina nanoparticles

Nanocrystalline and amorphous Ni–W coatings containing Al₂O₃ nanoparticles were electrodeposited from three different ammoniacal citrate baths by direct current (DC) method. The effects of nanoparticles on compositional, structural and morphological features of Ni–W coatings were investigated. The effects of bath chemical composition and current density on codeposition behavior of nanoparticles were also studied. Guglielmi model for particle deposition was applied to identify the kinetics of particle deposition. The presence of nanoparticles may affect on coating grain size, tungsten content and the rate of metal deposition. In addition, nanoparticles can result in more compact coatings with fewer defects. The extent of these effects depends on bath chemical composition and may be influenced by the synergistic effect of Ni on deposition of W. It was also found that the kinetics of particle deposition and the effect of current density on codeposition behavior of nanoparticles are highly dependent on bath chemical composition.     

Responsive plasma polymerized ultrathin nanocomposite films

The plasma polymerization of NIPAAM and titanium isopropoxide monomers into responsive ultrathin films with responsive optical properties using plasma enhanced chemical vapor deposition is reported. The composite ultrathin films possess a large window for potential changes in their refractive index from 1.60 to 1.95. We demonstrated that these polymer films exhibit fast (transition time below 2 s), large, reversible, and repeatable changes to their thickness and refractive index as a function of periodic environmental humidity changes.     

Hybrid electrochemical/chemical synthesis of quantum dots

The "electrochemical/chemical method" (or "E/C method") is a new wet chemical method for synthesizing semiconductor quantum dots on graphite surfaces. The E/C synthesis of quantum dots composed of the generic semiconducting salt, MX, typically involves three steps: (1) electrochemical deposition of nanoparticles of the metal, M degrees, from a solution of metal ions, M(n)(+); (2) electrochemical oxidation of these metal particles to MO(n)()(/2), and; (3) displacement of the oxygen from MO(n)()(/2) using HX (for example) to yield nanoparticles of MX. This conversion from metal to metal oxide to metal salt occurs on a particle-by-particle basis; that is, each metal nanoparticle is converted into a semiconductor nanoparticle. E/C-synthesized beta-CuI and CdS quantum dots possess many of the attributes of quantum dots synthesized using molecular beam epitaxy, including epitaxial orientation on the graphite surface, a narrow size dispersion, and strong, particle size-tunable photoluminescence. However, the E/C method is faster, cheaper, and applicable to a greater number of materials.     

Optical fiber extrinsic refractometer to measure RI of samples in a high pressure and temperature systems: Application to wax and asphaltene precipitation measurements

An optical fiber extrinsic sensor for measurement of changes in the refractive index of liquids confined in chambers for high pressure and temperature experiments is described. One head sensor composed by two fibers is fixed in front of a high pressure and temperature cell filled with the sample. The operation principle is based in the reflectivity dependence in the refractive index of the glass–liquid interface. Excellent results and a sensitivity of 10⁻⁵ RI were obtained for pure liquids. The applicability of the sensor is demonstrated following the changes in the refractive index for pure liquids at different pressure and temperatures and by measuring the asphaltenes and wax precipitation in crude oils under pressure. The extrinsic probe designed for refractive index measurement proves to be a reliable tool for measuring heavy organics deposition in crude oils under high pressures and temperatures where the sample to be measured is not very accessible.     

Electrodeposition of polycrystalline ZnTe from simple and citrate-complexed acidic aqueous solutions

The cathodic electrodeposition of polycrystalline zinc telluride from aqueous acidic solutions of zinc sulphate and tellurite, under constant or pulsing voltage, is described. Various compositions of the bath were tested with respect to the Zn/Te precursor ratio, including addition of citrate buffer as a complexation agent. Metallic (Ni and Ti) and semiconductor (CdTe and CdSe) electrodes were used as cathode-substrates. The deposits were characterized by XRD, SEM-EDX and FTIR techniques. The formation of compact barrier layers of zinc blend, stoichiometric ZnTe or mixed (Zn,Cd)Te was attained. Pulse plating in a citrate-free bath and constant potential plating from a citrate bath were seen to have the most beneficial effect on the properties of the electrodeposits, as leading to improved microstructure of the ZnTe films, in terms of crystallinity and stoichiometry. Further, the employment of [1 1 1]-oriented CdTe or CdSe substrates featured an epitaxial growth of polycrystalline ZnTe films as well as an improved Zn/Te atomic ratio compared to the metallic substrates.     

Raman scattering by confined optical phonons in Si and Ge nanostructures

A microscopic theory of the Raman scattering based on the local bond-polarizability model is presented and applied to the analysis of phonon confinement in porous silicon and porous germanium, as well as nanowire structures. Within the linear response approximation, the Raman shift intensity is calculated by means of the displacement-displacement Green's function and the Born model, including central and non-central interatomic forces. For the porous case, the supercell method is used and ordered pores are produced by removing columns of Si or Ge atoms from their crystalline structures. This microscopic theory predicts a remarkable shift of the highest-frequency of first-order Raman peaks towards lower energies, in comparison with the crystalline case. This shift is discussed within the quantum confinement framework and quantitatively compared with the experimental results obtained from porous silicon samples, which were produced by anodizing p--type (001)-oriented crystalline Si wafers in a hydrofluoric acid bath.