Defect passivation by hydrogen reincorporation for silicon quantum dots in SiC/SiOx hetero-superlattice

The SiC/SiO_x hetero-superlattice (HSL) consisting of alternating near-stoichiometric SiC barrier layers for the electrical transport and silicon rich SiO_x matrix layers for the quantum dot formation is a promising approach to the realization of silicon quantum dot (Si–QD) absorbers for 3rd generation solar cells. However, additional defect states are generated during post deposition annealing needed for the Si–QD formation causing an increase in sub-band gap absorption and a decrease in PL intensity. Proper passivation of excess defects is of major importance for both the optical and electrical properties of the SiC/SiO_x HSL Si–QD absorber. In this work, we investigate the effectiveness of the hydrogen reincorporation achieved with hydrogen plasma in a plasma-enhanced chemical vapor deposition (PECVD) reactor, hydrogen dissociation catalysis in hot-wire chemical vapor deposition (HWCVD) reactor and annealing in forming gas atmosphere (FGA). Both the HSL samples and single layer reference samples are tested. The passivation quality of the hydrogen reincorporation was examined by comparing electrical and optical properties measured after deposition, after annealing and after passivation. In addition, the formation of Si–QDs in SiC/SiO_x HSL was evaluated using high resolution transmission electron microscopy. We demonstrated that hydrogen can be successfully reincorporated into the annealed HSL sample and its single layer reference samples. FGA passivation is most effective for SiO_1.2 single layers and HSL samples. Passivation with PECVD appeared to be only effective for SiC single layers.     

Crystallization of silicon thin films by current‐induced joule heating using a tungsten overcoat

A modified crystallization process using current‐induced joule heating under vacuum is presented. A thin layer of high temperature resistant tungsten was sputtered on the amorphous silicon as the conducting and annealing medium. The thin film thickness was measured by α‐stepper. The high current density provided effective means in crystallizing the amorphous silicon layer. The crystalline morphology was studied by scanning electron microscopy (SEM) after Secco‐etch, transmission electron microscopy (TEM), and x‐ray diffraction (XRD), under different annealing conditions. The grain size was controlled in the range of 0.1‐0.5 μm and could be increased with annealing time. No tungsten silicide was found. Some defects were formed due to electron‐migration effect near the electrodes. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Thermally activated stress relief in garnet layers grown by liquid phase epitaxy

The lattice misfit of (Lu, Tb)₃Fe₅O₁₂ epitaxial layers grown in compression on Gd₃Ga₅O₁₂ substrates has been found to decrease as a result of annealing at temperatures between 1000 and 1300°C. The deformation rate is thermally activated and depends on the degree of compressive misfit stress at the annealing temperature, the layer thickness and the reducing nature of the anneal atmosphere. Layers which were in tension at the annealing temperature (obtained by using Y₃Fe₅O₁₂ as the substrate material) did not exhibit stress relief. The process has been found to occur nonhomogeneously by the formation of regions of almost total relief which grow and multiply with continued annealing. The shape symmetry of these regions is consistent with dislocation climb in {112} planes. The results are interpreted in terms of a mechanism involving dislocation climb loops (∽1μm diameter) which develop as a result of the formation of oxygen vacancies.     

溅射制备不同厚度Pb(Zr0.52Ti0.48)O3薄膜结晶态的研究

研究了射频磁控溅射的Pb(Zr0.52Ti0.48)O3(PZT52/48)薄膜在退火晶化时,厚度对其结晶态及表面形貌的影响.首先利用Materials Studio软件对PZT分子进行了模拟,并模拟了X射线衍射(XRD)得到PZT的特征峰图;实验上,采用退火炉对不同厚度的PZT(52/48)薄膜进行了不同温度及时间的退火;接着采用XRD对各样片薄膜进行了结晶物相分析;采用FIB对部分样片薄膜表面形貌进行了观察.实验结果显示,薄膜的厚度及退火条件在一定程度上对其结晶态的影响是一致的;对于一定厚度的薄膜,合适且相同的退火(650 ℃)条件都可以使其形成单一的PZT(52/48)物相;二次退火对较厚薄膜结晶化有一定的作用,但随着溅射薄膜厚度的增加而累加了内应力,退火后形成有PZT(52/48)物相的较厚薄膜表面出现裂纹越明显.     

Characterization of the structure of porous germanium layers by high-resolution X-ray diffractometry

The surface morphology and the structure of porous germanium layers obtained by chemical etching of n-type single-crystal Ge(111) substrates with their subsequent annealing in hydrogen atmosphere are studied by high-resolution X-ray diffractometry. It is established that upon etching a 1.5 to 2.0-μm-thick porous germanium layer is formed, which contains quasi-ordered microinhomogeneities in the form of elongated pits with characteristic dimensions of 1 μm and an average distance between them of 3–4 μm. The layer bulk has pores with radii ranging within 25–30 nm and nanocrystallites with an average size of 10 nm, with the average porosity being 56%.     

Deposition of thick silica-titania sol-gel films on Si substrates

A process for production of thick (>10 μm) titania-doped silica films on Si substrates by repetitive spin-coating of sol-gel material and rapid thermal annealing for 10 s in the range 800–1200°C is described. The dependence of overall thickness and etch rate in buffered HF on annealing temperature is described, and it is shown that films annealed at low (< 1175°C) temperatures have a relatively large thickness and etch rate. However, films having the properties of fully densified material (minimum thickness and etch rate) can be produced by subsequent consolidation. The film stress characteristics are similar to those phosphosilicate glass formed by the same process: films annealed below a critical temperature (< 1075°C) are under tensile stress at the annealing temperature, and crack before a thick film can be built up. Refractive index data are given; these show that only fully consolidated films have the refractive index expected from their SiO₂ and TiO₂ compositions. Finally, discrepancies in results for thickness of unconsolidated single-layer and multilayer films are explained using a simple model that accounts for the effect of cumulative densification.     

Variation of strain in granular GaAs:MnAs layers

Granular GaAs(MnAs) layers with different Mn concentration and various layer thickness were grown by MBE method and subjected to annealing at 500°C under ambient and enhanced hydrostatic pressure. Distinct influence of hydrostatic pressure applied during annealing on strain state of layers as well as on hexagonal MnAs inclusions was found. Pressure induced strain of inclusions is related to different bulk moduli of GaAs and of hexagonal MnAs. Formation of hexagonal inclusions depends on concentration of Mn in interstitial position in as-grown samples.     

Growth and properties of semi-polar GaN on a patterned silicon substrate

Adopting anisotropy etching method, a (1 1 1) facet of Si is obtained on a Si substrate and selective area growth (SAG) of GaN is performed with metal-organic vapor phase epitaxy on the facet. The epitaxial lateral overgrowth of (1 1¯ 0 1), (1 1 2¯ 2) GaN is investigated on (0 0 1) and (1 1 3) Si substrate, respectively, and the incorporation properties of Si, C, and Mg elements are discussed in relation to the atomic configuration on the surface. Analyzing the optical and electrical properties of C-doped (1 1¯ 0 1) GaN layer, it is shown that carbon creates a shallow acceptor level. On the thus prepared (1 1¯ 0 1) GaN layer, a light emitting diode (LED) with a C-doped p-type layer is fabricated.     

Nucleation,Glide Velocity and Blocking of Misfit Dislocations in SiGe/Si

Relaxation of strained layer systems is still not well understood. It is time dependent and changes considerably for samples with different growth history. This has to be discussed in terms of nucleation, glide velocity and blocking of misfit dislocations. We have investigated these phenomena at samples with SiGe layer thicknesses ranging from 60 nm up to 120 nm grown by molecular beam epitaxy (MBE) or chemical vapor deposition (CVD) by means of X-ray topography. The samples were annealed at temperatures between 500° and 600° C. Nucleation of misfit dislocations is heterogeneous and the rate is obviously dependent on layer strain and thickness. A quantified nucleation rate was not yet accessible, mainly due to the preferential formation of dislocation bundles. The propagation velocities of misfit dislocation segments were measured during annealing by means of synchrotron radiation plane wave topography (reflection geometry). The values agree well with theory and there is no evidence that they depend on growth regime. It is shown that the interaction of propagating misfit dislocations with crossing ones may lead to blocking or cross slip in different glide systems. These results are corroborated by investigations with atomic force and transmission electron microscopy.     

往复式电镀金刚石线锯切割单晶硅片特性研究

通过往复式电镀金刚石线锯切割单晶硅片实验,分析了切片表面的微观形貌特点,研究了锯丝速度与进给速度对硅片的表面粗糙度、总厚度偏差(TTV)、翘曲度与亚表面损伤层厚度(SSD)的影响规律.结果表明:线锯锯切时材料以脆性模式去除,锯切表面的微观形貌呈现部分沟槽与断续划痕,并存在大量凹坑;锯丝速度增大,进给速度减小,表面粗糙度与SSD减小;锯丝速度增大,进给速度增大,硅片的翘曲度也随之增大;硅片TTV值与锯丝速度和进给速度的匹配关系相关.     

Reduction of copper in soda-lime-silicate glass by hydrogen

The reduction of copper in soda-lime-silicate glasses by hydrogen was measured as a function of time and copper content within the temperature range 440 to 650°C. Copper is reduced to the metallic state in a surface layer whose thickness increases with time and temperature and decreases with copper content. A well developed periodical precipitation of copper particles is observed in the reduced layer. The reduction is accompanied by an alteration of the glass composition in which there is an increase of the copper content and a reduction of the calcium content. The growth kinetic of the reduced layer, followed by optical spectroscopy and measurement of the layer thickness, is analyzed with regard to the tarnishing model.     

分层沉积GaAs/SiO2纳米薄膜的结构和吸收光谱

应用射频磁控溅射方法分别在抛光硅片和石英玻璃片上分层沉积了GaAs/SiO2纳米薄膜.通过X射线衍射(XRD)、原子力显微镜(AFM)、扫描电子显微镜(SEM)及吸收光谱的测试,发现衬底温度、退火、氢掺杂等制备工艺对分层沉积的GaAs/SiO2纳米薄膜的微观结构和光学性质有明显的影响.本文对相关机理作了探讨.     

Low energy shifted photoluminescence of Er3+ incorporated in amorphous hydrogenated silicon–germanium alloys

Low energy shifted photoluminescence from isolated erbium ions incorporated into a-SiGe:H thin films is reported. The Er³⁺ are thermally diffused from an a-SiGe:H:Er layer to a-SiGe:H subsequently grown, both by magnetron sputtering. The photoluminescence observed is associated with transitions produced by erbium emission centers activated by the oxidation in a 1 h annealing process in air at 250 °C. The resultant Er³⁺ concentration observed from the a-SiGe:H is affected by the hydrogen concentration already present in the layer. It is observed that at higher hydrogen concentrations in a-SiGe:H the resultant amount of diffused Er³⁺ decreases. As a consequence of the resultant smaller density of erbium ions, the probability of having isolated Er³⁺ ions increases. In this last regime, a correlation with stronger photoluminescence is observed.     

Characterization of p-type ZnSe grown by MOVPE; excitonic emission lifetime measurements

Time-resolved photoluminescence (TRPL) measurements are made on p-type nitrogen-doped ZnSe grown by photoassisted metalorganic vapor phase epitaxy (MOVPE) together with post-growth thermal annealing, in order to investigate optical quality of the layers. It is suggested that the annealing degrades the layer quality and the MOVPE samples have more non-radiative recombination centers compared with MBE samples. A key issue for high quality p-ZnSe by MOVPE seems to be optimization of annealing conditions.     

Silicon on spinel: The interaction between deposition constituents and the substrate surface

The examination of the growth of silicon on flame fusion and Czochralski spinel prior to complete coverage of the substrate provides information on the chemical interaction between the deposition constituents and the substrate material. The flame fusion spinel appears to be eroded primarily by silicon, while the Czochralski spinel is eroded by both hydrogen and silicon. The hole mobilities in (111) silicon deposited in helium on the Czochralski spinel are similar to the mobilities in (111) silicon deposited in hydrogen on the flame fusion spinel. The semiconducting properties of silicon on the Czochralski spinel are degraded by annealing the substrate in hydrogen, and are unaffected by annealing the substrate in helium. The substrate surface work damage appears to be removed as the result of reduction of the spinel by silicon during the deposition of silicon on the Czochralski spinel in helium. Both the electrical data of 1 μm thick films and the physical nature of the deposits prior to complete coverage of the substrate lead to the conclusion that the hole mobilities in silicon on spinel are limited primarily by the impurities introduced into the deposit by reaction of the substrate with the deposition constituents, and that the impurities are incorporated into the deposit mainly prior to complete coverage of the surface and are concentrated in a thin layer in the silicon near the silicon-substrate interface.     

Spectroscopic ellipsometry study of nickel induced crystallization of a-Si

The aim of this work is to present a spectroscopic ellipsometry study focused on the annealing time effect on nickel metal induced crystallization of amorphous silicon thin films. For this purpose silicon layers with 80 and 125 nm were used on the top of which a 0.5 nm Ni thick layer was deposited. The ellipsometry simulation using a Bruggemann Effective Medium Approximation shows that films with 80 nm reach a crystalline fraction of 72% after 1 h annealing, appearing to be full crystallized after 2 h. No significant structural improvement is detected for longer annealing times. On the 125 nm samples the crystalline volume fraction after 1 h is only around 7%, requiring 5 h to get a similar crystalline fraction than the one achieved with the thinner film. This means that the time required for full crystallization will be strongly determined by the Si layer thickness. Using a new fitting approach the Ni content within the films was also determined by SE and related to the silicon film thickness.     

Thermal annealing of a-Si/Au superlattice thin films

The superlattice films, which consist of amorphous silicon (a-Si) and amorphous gold (Au), were prepared by ultra-high vacuum evaporation system. The first layer was grown a-Si with a thickness of 4.2 nm and the second layer was grown Au with a thickness of 0.8 nm. Thermal annealing was performed at 473, 673, and 873 K, respectively. The structural properties of the films were investigated using transmission electron microscope (TEM), X-ray diffraction (XRD), and Raman scattering spectroscopy. The electrical property was assessed by the temperature dependence of electrical conductivity. A crystallization of Si and a forming of Au nanoparticles were observed in all of the annealing films. The crystalline volume fraction reached 70% by annealing time for 15 min. An average diameter of the Au nanoparticles embedded in Si matrix also increased with increasing the annealing temperature. At annealing temperature above 873 K, Au atoms migrated toward the film surface. It was observed that the electrical conductivity changed in several temperatures.     

溶胶-凝胶法制备紫外及蓝光双截止润眼镀膜玻璃

采用溶胶-凝胶法,在3 mm厚的普白玻璃含锡面镀制镶嵌Ag纳米粒子的氧化硅薄膜,达到吸收蓝光的效果,在其非锡面镀制纤锌矿结构的氧化锌薄膜,达到阻隔紫外效果.通过双膜层的相互作用,达到对紫外和短波蓝光有效阻隔吸收,从而获得具有紫外蓝光防护及润眼功能的镀膜玻璃.研究了热处理温度和膜层厚度对近紫外和蓝光阻隔率的影响.结果表明:随着退火温度的升高,膜层更加致密,且退火温度越高,蓝光的吸收率也逐渐提高,吸收峰位红移.利用浮法玻璃本体的富锡表面还原AgNO3成Ag纳米粒子分散镶嵌在氧化硅薄膜的结构,能有效吸收380～450 nm的短波蓝光.实验样品呈现出美观的淡金黄色,且随着膜厚的增大,金黄色程度逐渐加深.以样品a为例,所制备的氧化锌膜层为稳定的纤锌矿结构,膜厚为438 nm,表面为球状颗粒,对380 nm以下的紫外光阻隔率为98.83;;所制备氧化硅薄膜厚为200 nm,表面致密,对380～450 nm的蓝光阻隔率为90.73;,样品整体450～780 nm可见光透过率为77.8;.     

磨料形貌及分散介质对4H碳化硅晶片研磨质量的影响研究

研磨作为4H碳化硅(4H-SiC)晶片加工的重要工序之一，对4H-SiC衬底晶圆的质量具有重要影响。本文研究了金刚石磨料形貌和分散介质对4H-SiC晶片研磨过程中材料去除速率和面型参数的影响，基于研磨过程中金刚石磨料与4H-SiC晶片表面的接触情况，推导出简易的晶片材料去除速率模型。研究结果表明，磨料形貌显著影响4H-SiC晶片的材料去除速率，材料去除速率越高，晶片的总厚度变化(TTV)越小。由于4H-SiC中C面和Si面的各向异性，4H-SiC晶片研磨过程中C面的材料去除速率高于Si面。在分散介质的影响方面：水基体系研磨液的Zeta电位绝对值较高，磨料分散均匀，水的高导热系数有利于控制研磨过程中的盘面温度；乙二醇体系研磨液的Zeta电位绝对值小，磨料易发生团聚，增大研磨过程的磨料切入深度，晶片的材料去除速率提高，晶片最大划痕深度随之增大。     

Comment on ‘Post UV irradiation annealing of E′ centers in silica controlled by H2 diffusion’ by M. Cannas et al. [J. Non-Cryst. Solids 337 (2004) 9–14]

In the paper by Cannas et al. [M. Cannas, S. Costa, R. Boscaino, F.M. Gelardi, J. Non-Cryst. Solids 337 (2004) 9] the simplest version of the Waite theory of diffusion limited reactions was applied to the post irradiation annealing of E′ centers by molecular hydrogen diffusing in a silica matrix. This version of the Waite theory does not take into account limitations arising from the rate of the chemical process between reactants but assumes that the annealing kinetics is limited by the diffusion only. An attempt to fit the annealing rate determined experimentally to that calculated from this version of the Waite theory led to an unrealistically small value of the capture radius. To clarify this issue, a more advanced version of the Waite theory, which takes into account the viability of the chemical reaction between H2 and E′ centers, should be used. In this comment such a version of the Waite theory is outlined and applied to an interpretation of the experimental data reported in [M. Cannas, S. Costa, R. Boscaino, F.M. Gelardi, J. Non-Cryst. Solids 337 (2004) 9]. A rigorous argument of the hypothesis introduced in paper [M. Cannas, S. Costa, R. Boscaino, F.M. Gelardi, J. Non-Cryst. Solids 337 (2004) 9] that the annealing kinetics of E′ centers is not limited by the diffusion of H₂ molecules but is defined by the rate of the chemical reaction itself is presented.