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1
Thelander, Erik. "Epitaxial Ge-Sb-Te Thin Films by Pulsed Laser Deposition." Doctoral thesis, Universitätsbibliothek Leipzig, 2015. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-164106.
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This thesis deals with the synthesis and characterization of Ge-Te-Sb (GST) thin films. The films were deposited using a Pulsed Laser Deposition (PLD) method and mainly characterized with XRD, SEM, AFM and TEM.
For amorphous and polycrystalline films, un-etched Si(100) was used. The amorphous films showed a similar crystallization behavior as films deposited with sputtering and evaporation techniques.
When depositing GST on un-etched Si(100) substrates at elevated substrate temperatures (130-240°C), polycrystalline but highly textured films were obtained. The preferred growth orientation was either GST(111) or GST(0001) depending on if the films were cubic or hexagonal.
Epitaxial films were prepared on crystalline substrates. On KCl(100), a mixed growth of hexagonal GST(0001) and cubic GST(100) was observed. The hexagonal phase dominates at low temperatures whereas the cubic phase dominates at high temperatures. The cubic phase is accompanied with a presumed GST(221) orientation when the film thickness exceeds ~70 nm. Epitaxial films were obtained with deposition rates as high as 250 nm/min.
On BaF2(111), only (0001) oriented epitaxial hexagonal GST films are found, independent of substrate temperature, frequency or deposition background pressure. At high substrate temperatures there is a loss of Ge and Te which shifts the crystalline phase from Ge2Sb2Te5 towards GeSb2Te4. GST films deposited at room temperature on BaF2(111) were in an amorphous state, but after exposure to an annealing treatment they crystallize in an epitaxial cubic structure.
Film deposition on pre-cleaned and buffered ammonium fluoride etched Si(111) show growth of epitaxial hexagonal GST, similar to that of the deposition on BaF2(111). When the Si-substrates were heated directly to the deposition temperature films of high crystal-line quality were obtained. An additional heat treatment of the Si-substrates prior to deposition deteriorated the crystal quality severely.
The gained results show that PLD can be used as a method in order to obtain high quality epitaxial Ge-Sb-Te films from a compound target and using high deposition rates.
2
Ryu, Yung-ryel. "Study of epitaxial ZnSe films synthesized by pulsed deposition /." free to MU campus, to others for purchase, 1998. http://wwwlib.umi.com/cr/mo/fullcit?p9901275.
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Ye, Liang. "Rapid thermal CVD of epitaxial silicon from dichlorosilane source." Thesis, Queen's University Belfast, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.333849.
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Woo, Juhyun. "Growth of epitaxial zirconium carbide layers using pulsed laser deposition." [Gainesville, Fla.] : University of Florida, 2005. http://purl.fcla.edu/fcla/etd/UFE0013064.
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Vasilic, Rastko. "Epitaxial growth by monolayer restricted galvanic displacement." Diss., Online access via UMI:, 2006.
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Stallcup, Richard E. "Scanning Tunneling Microscopy of Homo-Epitaxial Chemical Vapor Deposited Diamond (100) Films." Thesis, University of North Texas, 2000. https://digital.library.unt.edu/ark:/67531/metadc2446/.
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Atomic resolution images of hot-tungsten filament chemical-vapor-deposition (CVD) grown epitaxial diamond (100) films obtained in ultrahigh vacuum (UHV) with a scanning tunneling microscope (STM) are reported. A (2x1) dimer surface reconstruction and amorphous atomic regions were observed on the hydrogen terminated (100) surface. The (2x1) unit cell was measured to be 0.51"0.01 x 0.25"0.01 nm2. The amorphous regions were identified as amorphous carbon. After CVD growth, the surface of the epitaxial films was amorphous at the atomic scale. After 2 minutes of exposure to atomic hydrogen at 30 Torr and the sample temperature at 500° C, the surface was observed to consist of amorphous regions and (2x1) dimer reconstructed regions. After 5 minutes of exposure to atomic hydrogen, the surface was observed to consist mostly of (2x1) dimer reconstructed regions. These observations support a recent model for CVD diamond growth that is based on an amorphous carbon layer that is etched or converted to diamond by atomic hydrogen. With further exposure to atomic hydrogen at 500° C, etch pits were observed in the shape of inverted pyramids with {111} oriented sides. The temperature dependence of atomic hydrogen etching of the diamond (100) surface was also investigated using UHV STM, and it was found that it was highly temperature dependent. Etching with a diamond sample temperature of 200° C produced (100) surfaces that are atomically rough with no large pits, indicating that the hydrogen etch was isotropic at 200° C. Atomic hydrogen etching of the surface with a sample temperature of 500° C produced etch-pits and vacancy islands indicating an anisotropic etch at 500° C. With a sample temperature of 1000° C during the hydrogen etch, the (100) surface was atomically smooth with no pits and few single atomic vacancies, but with vacancy rows predominantly in the direction of the dimer rows, indicating that the 1000° C etch was highly anisotropic. Raman spectroscopy was used as a temperature probe, and for determining film quality.
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Zaia, Gilberto Vitor. "Epitaxial growth of Si and 3C-SiC by chemical vapor deposition." [S.l. : s.n.], 2002. http://deposit.ddb.de/cgi-bin/dokserv?idn=966630424.
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Nutariya, Jeerapat. "Epitaxial thin film growth of Pt assisted by underpotential deposition phenomena." Thesis, University of Bristol, 2013. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616569.
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Fuel cells as green and sustainable energy sources are at the heart of future Hydrogen Economy. Current research is focused on creating highly active, stable and low content Pt catalysts to improve fuel cell performance up to standards suitable for commercialization. The development of bimetallic Pt structures is the most promising route for achieving this goal. Besides the lower-noble metal content, combination of Pt with other metal at the nano-scale .can result in enhancement of catalytic activity due to the combination of geometric and electronic effects. The main aim of this work is the development of a surface limited redox replacement (SLRR) protocol for the design of epitaxial Pt-films with atomic scale control of the structure. SLRR exploits underpotentially deposited (UPD) layer as sacrificial layer that is replaced by more-noble Pt through a surface-controlled limited red-ox (galvanic) reaction. Different from previously developed SLRR protocols this work explores the one-cell configuration setup as an alternative to improve the efficiency and quality of the growth. The conditions for growth have been optimized and monitored with automated control of the SLRR cycles. The successful growth of Pt films on Au has been demonstrated for SLRR growth via Pb UPD. The electrochemical characterisation showed that using Pb UPD as sacrificial layer produces epitaxial Pt films of high quality with no significant roughness evolution up to 10 layers. Scanning tunnelling microscopy (STM) examination of the morphology has shown that Pt was deposited in clusters of 5-10 nm size, homogeneously and uniformly distributed over the surface. Electrochemical quartz crystal microbalance (EQCM) showed high deposition , yield and the Pt(II):Pb replacement stoichiomentric ratio higher than expected 1 : 1, suggesting an extra reduction power present in the system. The compositional analysis of Pt layers grown by SLRR suggests incorporation of minimum 4 at% of Pb. The SLRR protocol for the homoepitaxial growth of Pt thin films using adsorbed H i.e. under potentially deposited H (H-UPD) has been developed. This work presents first application of the SLRR protocol using a nonmetal UPD system. EQCM experiments demonstrated steady displacement kinetics and a yield equal to the expected stoichiometric Pt(II):H exchange ratio (1 :2). Electrochemical and STM characterization of Pt films showed that the growth via SLRR of H-UPD results in increase of the surface roughness with the number of replacement steps. The roughness of SLRR deposited Pt films has been compared with films grown in the same solution at two constant overpotentials: with and without adsorbed H floating on the surface. The results showed clear advantages of using . the SLRR of H-UPD approach which generated films with two times lower roughness and better quality then the ones grown potentiostatically. The generality of the SLRR approach using H-UPD is validated by growth of Pt films on Pd ultrathin films on Au. The Pt films of well-defined thickness and structure grown by SLRR of Pb UPD have been used in a fundamental study of Pt dissolution during formic acid oxidation (FAO). A quantitative analysis of long term durability tests of Pt films has been conducted by potential cycling over an extended potential range. Direct proportionality between overall life and thickness of the catalyst has been observed. The characteristic stages of the activity decay were correlated with the characteristic electrochemical behaviour during FAO and the surface morphology examined by the atomic force microscopy. An average Pt dissolution rate of 1.90±O.33 ng.cm-2.cycle-1 has been determined during FAO which . was almost four times faster than the rate under the same conditions in the background solution. This study suggests that Pt dissolution mechanism during FAO is influenced in by reaction intermediates and processes on the surface.
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Gower, Aaron E. (Aaron Elwood). "Integrated model-based run-to-run uniformity control for epitaxial silicon deposition." Thesis, Massachusetts Institute of Technology, 2001. http://hdl.handle.net/1721.1/16787.
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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2001.Also available online at the MIT Theses Online homepage
Includes bibliographical references (p. 241-247).
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Semiconductor fabrication facilities require an increasingly expensive and integrated set of processes. The bounds on efficiency and repeatability for each process step continue to tighten under the pressure of economic forces and product performance requirements. This thesis addresses these issues and describes the concept of an "Equipment Cell," which integrates sensors and data processing software around an individual piece of semiconductor equipment. Distributed object technology based on open standards is specified and utilized for software modules that analyze and improve semiconductor equipment processing capabilities. A testbed system for integrated, model-based, run-to-run control of epitaxial silicon (epi) film deposition is developed, incorporating a cluster tool with a single-wafer epi deposition chamber, an in-line epi film thickness measurement tool, and off-line thickness and resistivity measurement systems. Automated single-input-single-output, run-to-run control of epi thickness is first demonstrated. An advanced, multi-objective controller is then developed (using distributed object technology) to provide simultaneous epi thickness control on a run-to-run basis using the in-line sensor, as well as combined thickness and resistivity uniformity control on a lot-to-lot basis using off-line thickness and resistivity sensors.
(cont.) Control strategies are introduced for performing combined run-to-run and lot-to-lot control, based on the availability of measurements. Also discussed are issues involved with using multiple site measurements of multiple film characteristics, as well as the use of time-based inputs and rate-based models. Such techniques are widely applicable for many semiconductor processing steps.
by Aaron Elwood Gower-Hall.
Ph.D.
10
Yamaguchi, Iwao. "Preparation of epitaxial oxide films on sapphire substrates by metal organic deposition." 京都大学 (Kyoto University), 2009. http://hdl.handle.net/2433/124565.
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McClure, Adam Marc. "Epitaxial thin film deposition of magnetostrictive materials and its effect on magnetic anisotropy." Diss., Montana State University, 2012. http://etd.lib.montana.edu/etd/2012/mcclure/McClureA0512.pdf.
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Magnetostriction means that the dimensions of a material depend on its magnetization. The primary goal of this dissertation was to understand the effect of magnetostriction on the magnetic anisotropy of single crystal magnetostrictive thin films, where the epitaxial pinning of the material to a substrate could inhibit its conversion to new dimensions. In order to address this goal, several Fe-based binary alloys were deposited onto various substrates by molecular beam epitaxy. The samples were characterized by an array of techniques including electron diffraction, Rutherford backscattering, vibrating sample magnetometry, ferromagnetic resonance, and x-ray absorption spectroscopies. The attempted growths of crystalline magnetostrictive thin films resulted in successful depositions of Fe 1-xGa x and Fe 1-xZn x. Depositions onto MgO(001) substrates result in an in-plane cubic magnetic anisotropy, as expected from the cubic symmetry of the Fe-based thin films, and a strong out-of-plane uniaxial anisotropy that forces the magnetization to lie in the plane of the films. Depositions onto ZnSe/GaAs(001) substrates feature an additional in-plane uniaxial anisotropy. The magnitudes and signs of the in-plane anisotropies depend on the Ga content. Furthermore, the cubic anisotropy constant of Fe 1-xGa x samples deposited onto MgO substrates switches sign at a lower Ga concentration than is seen in bulk Fe 1-xGa x. The effect on the magnetic anisotropy of depositing a magnetostrictive material as an epitaxial thin film is influenced by the material's magnetostrictive properties and the substrate upon which it is deposited. In particular, pinning a magnetoelastic material to a substrate will modify its cubic anisotropy, and depositions on substrates compliant to an anisotropic strain relaxation may result in a strong in-plane uniaxial anisotropy. 'Co authored by Steven Albert, Tino Jaeger, Hongyan Li, Paul Rugheimer, Juergen A. Schaefer, Yves U. Idzerda, Elke Arenholz, Hongyan Li, Gerrit van der Laan, Damon A. Resnick, Christopher M. Kuster.'
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Shibahara, Kentaro. "EPITAXIAL GROWTH OF SiC BY CHEMICAL VAPOR DEPOSITION AND APPLICATION TO ELECTRONIC DEVICES." Kyoto University, 1988. http://hdl.handle.net/2433/162216.
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Wang, Chao-Hsiung. "The growth of thin film epitaxial oxide-metal heterostructures." Thesis, University of Cambridge, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.368667.
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Vankova, Viera. "Metalorganic vapour phase epitaxial growth and characterisation of Sb-based semiconductors." Thesis, Nelson Mandela Metropolitan University, 2005. http://hdl.handle.net/10948/d1019678.
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This study focuses on the growth and characterization of epitaxial InAs and InAs1-xSbx. Layers are grown on InAs, GaAs and GaSb substrates by metalorganic vapour phase epitaxy, using trimethylindium, trimethylantimony and arsine as precursors. The growth parameters (V/III ratio, Sb vapour phase compositions) are varied in the temperature range from 500 ºC to 700 ºC, in order to study the influence of these parameters on the structural, optical and electrical properties of the materials. The layers were assessed by X-ray diffraction, electron and optical microscopy, photoluminescence and Hall measurements. Furthermore, the influence of hydrogenation and annealing on the electrical and optical properties of GaSb was investigated. It is shown that the growth temperature and the V/III ratio play a vital role in the resulting surface morphology of homoepitaxial and heteroepitaxial InAs layers. Growth at low temperatures is found to promote three-dimensional growth in both cases, with improvements in the surface morphologies observed for higher growth temperatures. All the investigated epilayers are n-type. It is shown that the electrical properties of heteroepitaxial InAs epilayers are complicated by a competition between bulk conduction and conduction due to a surface accumulation and an interface layer. The low temperature photoluminescence spectra of homoepitaxial InAs are dominated by two transitions. These are identified as band-to-band/excitonic and donor-acceptor recombination. The incorporation efficiency of antimony (Sb) into InAs1-xSbx is dependent on the growth temperature and the V/III ratio. Under the growth conditions used in this study, the incorporation efficiency of Sb is controlled by the thermal stability of the two constituent binaries (i.e. InAs and InSb). Changes in the low temperature photoluminescence spectra are detected with increasing x. From temperature and laser power dependent measurements, the highest energy line is attributed to band-to-band/excitonic recombination, while the peak appearing approximately 15 meV below this line is assigned to donor-acceptor recombination. The origin of an additional “moving” peak observed for higher Sb mole fraction x is tentatively attributed to quasi-donor-acceptor-recombination, arising from increased impurity/defect concentrations and a higher compensation ratio in the material. However, the unusual behaviour of this peak may also be ascribed to the presence of some degree of ordering in InAsSb. The exposure of a semiconductor to a hydrogen plasma usually leads to the passivation of shallow and deep centres, thereby removing their electrical and optical activity. In this study, the passivation and thermal stability of the native acceptor in p-type GaSb is also investigated. It is shown that this acceptor can be passivated, where after improvements in the electrical and optical properties of GaSb are observed. Upon annealing the passivated samples above 300 °C, the acceptor is reactivated.
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Bouilly, Guillaume Jacques. "Synthesis and characterization of transition metal oxides and oxyhydrides using epitaxial thin films deposition." 京都大学 (Kyoto University), 2015. http://hdl.handle.net/2433/200450.
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Patchett, David. "Germanium-tin-silicon epitaxial structures grown on silicon by reduced pressure chemical vapour deposition." Thesis, University of Warwick, 2016. http://wrap.warwick.ac.uk/93459/.
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Crystalline germanium-tin (GeSn) binary alloys have been subject to a significant research effort in recent years. This research effort is motivated by the myriad of potential applications that GeSn alloys offer. Crystalline epitaxial layers of GeSn and silicon-germanium-tin (SiGeSn) have been grown onto Si(001) substrates on a relaxed Ge buffer using reduced pressure CVD and commercially available precursors. X-ray diffraction, transmission electron microscopy, atomic force microscopy, secondary ion mass spectrometry and Raman spectroscopy were used to determine layer composition, layer thickness, crystallinity, degree of strain relaxation, surface features and roughness of the samples investigated in this work. The epilayers produced have been both fully strained to their growth platform and partially relaxed. The Sn fraction of the alloy layers varied from 1 to 12 at. % Sn. Using N2 as the carrier gas during growth is observed to inhibit Ge1-xSnx growth. Off-axis substrates are determined to hinder the production of crystalline layers of GeSn. In-situ material characterization of GeSn layers during thermal treatment has identified the existence of a critical temperature for higher Sn fraction layers, beyond which the material quality degrades rapidly. This critical temperature is dependent on the layer composition, layer thickness, layer strain state and annealing environment. Layers of germanium-tin-oxide are produced by thermal oxidation and shown to have similar oxide formation rates to pure Ge. The low thermal budget limit for the high Sn fraction alloys has driven research into forming Ohmic metal contacts on GeSn layers with processes limited to low temperatures. Gold is determined to be the optimum electrical contact material.
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Chang, Bertha Pi-Ju. "Deposition and planarization of epitaxial oxide thin films for high temperature superconducting device applications." Thesis, Massachusetts Institute of Technology, 1995. http://hdl.handle.net/1721.1/38087.
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Borovikov, Valery V. "Multi-scale Simulations of Thin-Film Metal Epitaxial Growth." University of Toledo / OhioLINK, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=toledo1216928358.
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Yan, Li. "Two phase magnetoelectric epitaxial composite thin films." Diss., Virginia Tech, 2009. http://hdl.handle.net/10919/30130.
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Magnetoelectricity (ME) is a physical property that results from an exchange between polar (electric dipole) and spin (magnetic dipole) subsystem: i.e., a change in polarization (P) with application of magnetic field (H), or a change in magnetization (M) with applied electric field (E). Magnetoelectricity can be found both in single phase and composite materials. Compared with single phase multiferroic materials, composite multiferroics have higher ME effects. Through a strictive interaction between the piezoelectricity of the ferroelectric phase and the magnetostriction of the ferromagnetic phase, said multiferroic composites are capable of producing relatively large ME coefficients.
This Dissertation focused on the deposition and characterization of two-phase composite magnetoelectric thin films. First, single phase ferroelectric thin films were studied to improve the multiferroic properties of the composite thin films. Then structural, ferroelectric, ferromagnetic, and magnetoelectric properties of composite thin films were researched. Finally, regular nano-array composite films were deposited and characterized.
First, for single phase ferroelectric thin films, the phase stability was controlled by epitaxial engineering. Because ferroelectric properties are strongly related to their crystal structure, it is necessary to study the crystal structures in single phase ferroelectric thin films. Through constraint of the substrates, the phase stability of the ferroelectric thin films were able to be altered. Epitaxial thin-layers of Pb(Fe1/2Nb1/2)O3 (or PFN) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, orthorhombic, and rhombohedral respectively. The larger constraint stress induces higher piezoelectric constants in tetragonal PFN thin film. Epitaxial thin-layers of Pb(Zr0.52Ti0.48)O3 (or PZT) grown on (001), (110), and (111) SrTiO3 substrates are tetragonal, monoclinic C, and rhombohedral respectively. Enhanced ferroelectric properties were found in the low symmetry monoclinic phase. A triclinic phase in BFO was observed when it was deposited on tilted (001) STO substrates by selecting low symmetry (or interim) orientations of single crystal substrates.
Then, in two phase composite magnetoelectric thin films, the morphology stability was controlled by epitaxial engineering. Because multiferroic properties are strongly related to the nano-structures of the composite thin films, it is necessary to research the nano-structures in composite thin films. Nano-belt structures were observed in both BaTiO3-CoFe2O4 and BiFeO3-CoFe2O4 systems: by changing the orientation of substrates or annealing condition, the nano-pillar structure could be changed into nano-belts structure. By doing so, the anisotropy of ferromagnetic properties changes accordingly. The multi-ferroic properties and magnetoelectric properties or (001), (110) and (111) self-assembled BiFeO3-CoFe2O4 nano-composite thin film were also measured.
Finally, the regular CoFe2O4-BiFeO3 nano-array composite was deposited by pulsed laser deposition patterned using a focused ion beam. Top and cross-section views of the composite thin film showed an ordered CoFe2O4 nano-array embedded in a BiFeO3 matrix. Multiferroic and magnetoelectric properties were measured by piezoresponse force microscopy and magnetic force microscopy. Results show (i) switching of the magnetization in ferromagnetic CoFe2O4 and of the polarization in ferroelectric BiFeO3 phases under external magnetic and electric field respectively, and (ii) changes of the magnetization of CoFe2O4 by applying an electric field to the BiFeO3 phase.Ph. D.
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Swanson, Kyle. "Epitaxial growth of silicon carbide on on-axis silicon carbide substrates using methyltrichlorosilane chemical vapor deposition." Thesis, Manhattan, Kan. : Kansas State University, 2008. http://hdl.handle.net/2097/719.
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Lee, Sam-Dong. "Crystalline properties of gallium oxide thin films epitaxially grown by mist chemical vapor deposition." 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/215547.
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Hållstedt, Julius. "Integration of epitaxial SiGe(C) layers in advanced CMOS devices." Doctoral thesis, KTH, Mikroelektronik och tillämpad fysik, MAP, 2007. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4498.
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Heteroepitaxial SiGe(C) layers have attracted immense attention as a material for performance boost in state of the art electronic devices during recent years. Alloying silicon with germanium and carbon add exclusive opportunities for strain and bandgap engineering. This work presents details of epitaxial growth using chemical vapor deposition (CVD), material characterization and integration of SiGeC layers in MOS devices. Non-selective and selective epitaxial growth of Si1-x-yGexCy (0≤x≤0.30, 0≤y≤0.02) layers have been performed and optimized aimed for various metal oxide semiconductor field effect transistor (MOSFET) applications. A comprehensive experimental study was performed to investigate the growth of SiGeC layers. The incorporation of C into the SiGe matrix was shown to be strongly sensitive to the growth parameters. As a consequence, a much smaller epitaxial process window compared to SiGe epitaxy was obtained. Incorporation of high boron concentrations (up to 1×1021 atoms/cm3) in SiGe layers aimed for recessed and/or elevated source/drain (S/D) junctions in pMOSFETs was also studied. HCl was used as Si etchant in the CVD reactor to create the recesses which was followed (in a single run) by selective epitaxy of B-doped SiGe. The issue of pattern dependency behavior of selective epitaxial growth was studied in detail. It was shown that a complete removal of pattern dependency in selective SiGe growth using reduced pressure CVD is not likely. However, it was shown that the pattern dependency can be predicted since it is highly dependent on the local Si coverage of the substrate. The pattern dependency was most sensitive for Si coverage in the range 1-10%. In this range drastic changes in growth rate and composition was observed. The pattern dependency was explained by gas depletion inside the low velocity boundary layer. Ni silicide is commonly used to reduce access resistance in S/D and gate areas of MOSFET devices. Therefore, the effect of carbon and germanium on the formation of NiSiGe(C) was studied. An improved thermal stability of Ni silicide was obtained when C is present in the SiGe layer. Integration of SiGe(C) layers in various MOSFET devices was performed. In order to perform a relevant device research the dimensions of the investigated devices have to be in-line with the current technology nodes. A robust spacer gate technology was developed which enabled stable processing of transistors with gate lengths down to 45 nm. SiGe(C) channels in ultra thin body (UTB) silicon on insulator (SOI) MOSFETs, with excellent performance down to 100 nm gate length was demonstrated. The integration of C in the channel of a MOSFET is interesting for future generations of ultra scaled devices where issues such as short channel effects (SCE), temperature budget, dopant diffusion and mobility will be extremely critical. A clear performance enhancement was obtained for both SiGe and SiGeC channels, which point out the potential of SiGe or SiGeC materials for UTB SOI devices. Biaxially strained-Si (sSi) on SiGe virtual substrates (VS) as mobility boosters in nMOSFETs with gate length down to 80 nm was demonstrated. This concept was thoroughly investigated in terms of performance and leakage of the devices. In-situ doping of the relaxed SiGe was shown to be superior over implantation to suppress the junction leakage. A high channel doping could effectively suppress the source to drain leakage.QC 20100715
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Souri, Maryam. "ELECTRONIC AND OPTICAL PROPERTIES OF METASTABLE EPITAXIAL THIN FILMS OF LAYERED IRIDATES." UKnowledge, 2018. https://uknowledge.uky.edu/physastron_etds/60.
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The layered iridates such as Sr2IrO4 and Sr3Ir2O7, have attracted substantial attention due to their novel electronic states originating from strong spin-orbit coupling and electron-correlation. Recent studies have revealed the possibilities of novel phases such as topological insulators, Weyl semimetals, and even a potential high-Tc superconducting state with a d-wave gap. However, there are still controversial issues regarding the fundamental electronic structure of these systems: the origin of the insulating gap is disputed as arising either from an antiferromagnetic ordering, i.e. Slater scheme or electron-correlation, i.e. Mott scheme. Moreover, it is a formidable task to unveil the physics of layered iridates due to the limited number of available materials for experimental characterizations.
One way to overcome this limit and extend our investigation of the layered iridates is using metastable materials. These materials which are far from their equilibrium state, often have mechanical, electronic, and magnetic properties that different from their thermodynamically stable phases. However, these materials cannot be synthesized using thermodynamic equilibrium processes. One way to synthesize these materials is by using pulsed laser deposition (PLD). PLD is able to generate nonequilibrium material phases through the use of substrate strain and deposition conditions. Using this method, we have synthesized several thermodynamically metastable iridate thin-films and have investigated their electronic and optical properties. Synthesizing and investigating metastable iridates opens a path to expand the tunability further than the ability of the bulk methods.
This thesis consists of four studies on metastable layered iridate thin film systems. In the first study, three-dimensional Mott variable-range hopping transport with decreased characteristic temperatures under lattice strain or isovalent doping has been observed in Sr2IrO4 thin films. Application of lattice strain or isovalent doping exerts metastable chemical pressure in the compounds, which changes both the bandwidth and electronic hopping. The variation of the characteristic temperature under lattice strain or isovalent doping implies that the density of states near the Fermi energy is reconstructed. The increased density of states in the Sr2IrO4 thin films with strain and isovalent doping could facilitate a condition to induce unprecedented electronic properties, opening a way for electronic device applications. In the second study, the effects of tuning the bandwidth via chemical pressure (i.e., Ca and Ba doping) on the optical properties of Sr2IrO4 epitaxial thin films has been investigated. Substitution of Sr by Ca and Ba ions exerts metastable chemical pressure in the system, which changes both the bandwidth and electronic hopping. The optical conductivity results of these thin films suggest that the two-peak-like optical conductivity spectra of the layered iridates originates from the overlap between the optically-forbidden spin-orbit exciton and the inter-site optical transitions within the Jeff = ½ band, which is consistent with the results obtained from a multi-orbital Hubbard model calculation. In the third study, thermodynamically metastable Ca2IrO4 thin- films have been synthesized. Since the perovskite structure of Ca2IrO4 is not thermodynamically stable, its bulk crystals do not exist in nature. We have synthesized the layered perovskite phase Ca2IrO4 thin- films from a polycrystalline hexagonal bulk crystal using an epitaxial stabilization technique. The smaller A-site in this compound compared to Sr2IrO4 and Ba2IrO4, increases the octahedral rotation and tilting, which enhance electron-correlation. The enhanced electron-correlation is consistent with the observation of increased gap energy in this compound. This study suggest that the epitaxial stabilization of metastable-phase thin-films can be used effectively for investigating complex-oxide systems. Finally, structural, transport, and optical properties of tensile strained (Sr1-xLax)3Ir2O7 (x = 0, 0.025, 0.05) thin-films have been investigated. While high-Tc superconductivity is predicted in the system, all of the samples are insulating. The insulating behavior of the La-doped Sr3Ir2O7 thin-films is presumably due to disorder-induced localization and ineffective electron-doping of La, which brings to light the intriguing difference between epitaxial thin films and bulk single crystals of the iridates. These studies thoroughly investigate a wide array of novel electronic and optical phenomena via tuning the relative strengths of electron correlation, electronic bandwidth, and spin-orbit coupling using perturbations such as chemical doping, and the stabilization of metastable phases in the layered iridates.
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Burriel, López Mónica. "Epitaxial Thin Films of Lanthanum Nickel Oxides: Deposition by PI-MOCVD, Structural Characterization and High Temperature Transport Properties." Doctoral thesis, Universitat Autònoma de Barcelona, 2007. http://hdl.handle.net/10803/3246.
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En los últimos años ha habido un interés creciente en el estudio de el compuesto La2NiO4+?, debido a sus propiedades como conductor mixto iónico-electrónico, que lo hacen adecuado para su utilización en dispositivos electroquímicos, tales como cátodo para pilas de combustible de óxido sólido a temperaturas intermedias (IT-SOFC), membranas de permeación o sensores de gas. La estructura de fase La2NiO4+? está formada por láminas de LaNiO3, de tipo perovskita, alternadas con láminas de LaO de tipo cloruro sódico, en las cuales puede incorporarse oxígeno sobreestequiométrico. Esta estructura laminar es la responsable de la anisotropía en las propiedades del La2NiO4+?, dando lugar a una conductividad iónica y electrónica que es entre dos y tres órdenes de magnitud superior a lo largo del plano ab, en comparación con la dirección del eje c.Este trabajo consiste en el estudio, desde un punto de vista fundamental, de películas delgadas epitaxiales de La2NiO4+? orientadas a lo largo del eje c y crecidas por la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD) sobre diferentes sustratos, con el fin de adquirir una mejor comprensión de sus características microestructurales, su variación con la tensión y la influencia de la tensión en las propiedades de transporte a elevada temperatura. Además, el crecimiento epitaxial permite la medida de las propiedades de las películas de La2NiO4+? en dos direcciones perpendiculares, obteniendo una medida directa de la anisotropía del material.
El La2NiO4+? es el primer miembro (n = 1) de la familia Ruddlesden-Popper Lan+1NinO3n+1, en la que la estructura de cada miembro está formada por un número n de bloques perovskita LaNiO3 alternados entre bloques LaO tipo cloruro sódico. Asimismo se han intentado depositar películas orientadas a lo largo del eje c de los miembros n = 2, 3 e ?, y se ha estudiado la variación las propiedades de transporte a lo largo de la serie Lan+1NinO3n+1.
En la tesis se realiza una introducción a los conductores mixtos iónicos-electrónicos (MIEC) y a los cátodos para pilas de combustible de óxido sólido (SOFC), como una posible aplicación del material La2NiO4+?. Se describen las propiedades más importantes de la fase La2NiO4+?, y de los miembros n =2, 3 e ? de la familia Lan+1NinO3n+1, así como el estado del arte de la preparación de películas delgadas de estos materiales.
A continuación se describe la técnica de deposición química en fase vapor de precursores organometálicos por inyección pulsada (PI-MOCVD), acompañada de una descripción detallada de los parámetros de depósito seleccionados, y del equipo PI-MOCVD utilizado. También se describen las técnicas utilizadas en la caracterización de las películas delgadas de Lan+1NinO3n+1.
Posteriormente se describen los parámetros de depósito optimizados para la deposición de películas epitaxiales de La2NiO4+? y se realiza una caracterización estructural, morfológica y microestructural en función del espesor de las películas, del sustrato utilizado y de la temperatura. También se detalla y describe la conductividad total de películas epitaxiales de diferente espesor medida. Para éstas películas se han medido, además, las propiedades de intercambio y de difusión de oxígeno utilizando dos técnicas diferentes: la técnica de intercambio de isótopos y la técnica de relajación de la conductividad. Los resultados de estas medidas se discuten en función de la microestructura de las películas.
Por último, se ha completado el estudio describiendo los primeros resultados de deposición de otros miembros de la familia Ruddlesden-Popper. La evolución de las propiedades de transporte total de las películas delgadas de Lan+1NinO3n+1 se han relacionado con el número de láminas tipo perovskita n.
In the last years there has been a great interest in the study of the La2NiO4+? compound due to its mixed ionic-electronic properties, which make it suitable in electrochemical devices, such as cathode in Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFC), permeation membranes or gas sensors. The La2NiO4+? phase structure is formed by perovskite-type LaNiO3 layers alternated with rocksalt-type LaO layers, in which hyperstoichiometric oxygen can be incorporated. This layered structure is responsible for the anisotropy in the La2NiO4+? properties, leading to electronic and ionic conductivity three orders of magnitude higher along the ab plane, in comparison with the c-axis direction.
This work is focused on the study, from a fundamental point of view, of epitaxial c-axis oriented La2NiO4+? thin films deposited by PI-MOCVD technique on different substrates, in order to achieve a better comprehension of the microstructural characteristics, their variation with strain and their influence in its high temperature transport properties. Moreover, the epitaxial growth of the films permits the measurement of the properties of the La2NiO4+? in two perpendicular directions, to have a direct inset of the anisotropy.
The La2NiO4+? phase is the n = 1 member of the Lan+1NinO3n+1 Ruddlesden-Popper family, in which the structure of each member is formed by a n number of perovskite layers alternated between rock-salt layers. We have also attempted to deposit c-axis oriented films of the n = 2, n = 3 and n = 1 members and studied the variation of the transport properties through the different members of the family.
First, Chapter 1 consists of an introduction to the mixed ionic-electronic conductors (MIEC) and to the solid oxide fuel cell (SOFC) cathodes, as a possible application of the La2NiO4+? material. The most remarkable properties of the La2NiO4+? phase, and of the n = 2, 3 and 1 members of the Lan+1NinO3n+1 family are analyzed, as well as the state of the art in the preparation of thin films of these materials.
In Chapter 2, the Metalorganic Chemical Vapor Deposition (MOCVD) technique is described, accompanied by a detailed description of the selected experimental deposition parameters and of the Pulsed Injection MOCVD equipment used. Chapter 3 summarizes all the techniques used for the Lan+1NinO3n+1 thin film characterization.
In Chapter 4, the optimized experimental parameters for the deposition of epitaxial La2NiO4+? thin films are described. Structural, morphological and microstructural characterization is performed as a function of film thickness, substrate used and temperature. Total conductivity of epitaxial layers is also described and discussed.
In Chapter 5 we have studied the oxygen exchange and transport of the La2NiO4+? thin films by two different techniques: the oxygen isotope exchange and the electrical conductivity relaxation. Results are discussed as a function of microstructure.
Finally, in Chapter 6, the study is completed describing the first results of the deposition of the other members of the Ruddlesden-Popper family. Evolution of the total conductivity properties of the Lan+1NinO3n+1 films has been related to the n number of perovskite layers.
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Mc, Grath Oran F. K. "Structural and magnetic properties of epitaxial W/Fe/W and Gd/Fe films grown by pulsed laser deposition." Université Joseph Fourier (Grenoble), 1994. http://www.theses.fr/1994GRE10209.
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Le but de cette these est d'etudier les proprietes structurales et magnetiques des couches epitaxiees de w/fe/w et gd/fe elaborees par depot laser pulse. La technique de depot laser pulse est presentee dans le premier chapitre. La croissance des couches minces est discutee dans le deuxieme chapitre puis l'analyse des proprietes structurales des couches elaborees est presentee dans le troisieme chapitre. Une revue des proprietes magnetiques des couches ultra-minces, telle que le moment magnetique, l'anisotropie et les excitations thermiques est presentee dans le quatrieme chapitre. La determination experimentale de ces proprietes magnetiques dans les couches de w/fe/w est discutee dans le cinquieme chapitre. Le couplage interfacial dans les couches de gd/fe est analyse dans le dernier chapitre
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Burriel, López Mónica. "Epitaxial thin films of lanthanum nickel oxides deposition by PI-MOCVD, structural characterization and high temperature transport properties." Saarbrücken VDM Verlag Dr. Müller, 2007. http://d-nb.info/988631342/04.
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Soler, Bru Laia. "Liquid-assisted ultrafast growth of superconducting films derived from chemical solutions." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667208.
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L'ús generalitzat de superconductors d'alta temperatura (HTS) en aplicacions a gran escala està, en part, encara limitat per l’elevat cost de fabricació de cintes recobertes (CCs). Amb la intenció d'aconseguir un avanç important per assolir un major rendiment, en aquesta tesi hem desenvolupat una tècnica innovadora que combina els beneficis de Deposició de Solucions Químiques (CSD) a baix cost amb les altes velocitats del creixement cristal·lí a partir de fases líquides. Es basa en la formació d'un líquid transitori derivat de solucions de carboxilats, aprofitant els obstacles cinètics per la cristal·lització de la fase d'equilibri.
En aquesta tesi doctoral, primer expliquem els fonaments del procés que condueix a la cristal·lització de YBa2Cu3O7-δ assistida per un líquid transitori; i després portem a terme una investigació detallada sobre aquesta tècnica. El "proof-of-principle" de la viabilitat d'aquesta nova aproximació es va aconseguir amb la disponibilitat dels forns tipus RTA que permeten rampes fins a 80ºC/s.
Les reaccions implicades en el procés s'observen amb mesures in situ i de microscòpia, entre altres. Primer, la piròlisi resultant de la barreja de propionats de Ba, Cu i Y a baixes temperatures (500ºC) és observada amb espectroscòpia in situ d’infraroig. A continuació, s’utilitza difracció de rajos-X amb llum de sincrotró per revelar les reaccions que tenen lloc per convertir el BaCO3, CuO i Y2O3 en la fase final, així com analitzar la nucleació i el creixement del YBa2Cu3O7-δ des del líquid transitori (TLAG).
Per dur a terme el procés, el pas de deposició es realitza amb mètodes d'impressió d'injecció de tinta o revestiment per rotació. Les característiques de les solucions s'han adaptat a la tècnica de deposició i es correlacionen amb la morfologia de la capa resultant.
A continuació s'han investigat diversos paràmetres per controlar la velocitat de la reacció limitant per l'eliminació del carbonat de bari amb l’objectiu d’evitar la retenció de carboni a les capes gruixudes epitaxials.
Posteriorment, s'estableixen els conceptes bàsics per a la comprensió dels mecanismes de nucleació i creixement del YBCO a partir de TLAG. Amb l'objectiu d'obtenir capes epitaxials de YBCO orientades en l’eix-c, es presenten diverses estratègies per controlar la força de cristal·lització. Els paràmetres rellevants són: la composició de la solució, la pressió d'oxigen, les rampes d’escalfament i les temperatures de creixement. Finalment, les condicions de cristal·lització es correlacionen amb les microestructures i propietats superconductores de les capes resultants.
Es presenten dos camins diferents per dur a terme el creixement mitjançant la formació de líquid. Un és a través d’un augment de temperatura a pressió d'oxígen constant (ruta-Temperatura). L’altre procés consisteix en dos passos (ruta-pO2). Per aquest últim, l'eliminació de BaCO3 es desvincula del creixement de YBCO mitjançant un salt en pO2.
Cal abordar diversos reptes en funció de la ruta. Alguns d’ells són: la reactivitat del líquid amb els substrats degut a la seva naturalesa altament corrosiva, o una mullabilitat inadequada.
Finalment, hem tingut èxit en obtenir pel·lícules fines de YBCO epitaxials d’entre 90-500 nm amb propietats superconductores molt elevades (Tc 90-92K, Jc fins a 5MA/cm2 a 77K), i velocitats de creixement fins a 100 nm/s, augmentat així en un factor 100 la velocitat de creixement de la metodologia de CSD convencional. Aquesta metodologia podria ser traslladada a altres materials.The widespread use of High Temperature Superconductors (HTS) into large scale applications is, in part, still limited by the high costs of coated conductors manufacturing. Aiming for a breakthrough to achieve high throughput, in this thesis we have developed a novel technique that combines the low cost benefits of Chemical Solution Deposition (CSD) with the very high growth rates of crystallization from liquid phases. It relies on the formation of a transient liquid derived from carboxylate solutions, taking advantage of the kinetic hindrances on crystallization to reach the equilibrium phase. In this dissertation, we first explain the basics of the process that leads to YBa2Cu3O7-δ crystallization assisted by a transient liquid and then we elaborate on the results of our investigation about this technique. The “proof-of-principle” of this new approximation viability has been achieved with the use of rapid thermal annealing furnaces, allowing heating rates up to 80ºC/s. The reactions involved in the process are observed with in situ measurements and microscopic analyses, among others. First, the pyrolysis of the Ba, Cu and Y propionates mixture at low temperatures (500ºC) is observed with in situ infrared spectroscopy. Then, time resolved X-ray diffraction with synchrotron light is used to reveal the reaction paths to convert the resulting BaCO3, CuO and Y2O3 to the final phase, as well as nucleation and growth of the YBa2Cu3O7-δ film from the transient liquid. To do so, the deposition step is performed with spin coating or Ink Jet printing methodologies. The solutions characteristics have been adapted to the deposition technique and correlated to the resulting film morphology. Then, several parameters have been investigated to control the rate limiting BaCO3, elimination reaction in order to avoid carbon retention in the final thick epitaxial films. Afterwards, the basic concepts for understanding the nucleation and growth mechanisms of YBCO with TLAG are set. With the aim of obtaining c-axis epitaxial YBa2Cu3O7-δ films, several strategies are presented to control the driving force for crystallization. The relevant parameters are solution composition, oxygen pressure, heating ramps and growth temperatures. Finally, the crystallization conditions are correlated to the resulting films microstructure and superconducting performances. Two different paths are presented to reach TLAG. A direct temperature raise at constant oxygen pressure (Temperature-route), or a two step process (pO2-route). For the latter, BaCO3 elimination is disentangled from YBa2Cu3O7-δ growth by a jump on pO2. Additionally, several challenges needed to be addressed depending on the route: liquid reactivity with the substrates due to its highly corrosive nature or improper wettability, are some of them. Finally, we have succeeded in obtaining highly epitaxial YBCO thin films of 90-500nm with very high superconducting performances (Tc 90-92K, Jc up to 5MA/cm2 at self-field and 77K), at growth rates up to 100nm/s, increased by a factor 100 from those reported with conventional CSD. This methodology could be applied to other materials.
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Miya, Senzo Simo. "Atmospheric pressure metal-organic vapour phase epitaxial growth of InAs/GaSb strained layer superlattices." Thesis, Nelson Mandela Metropolitan University, 2013. http://hdl.handle.net/10948/d1020866.
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The importance of infrared (IR) technology (for detection in the 3-5 μm and 8-14 μm atmospheric windows) has spread from military applications to civilian applications since World War II. The commercial IR detector market in these wavelength ranges is dominated by mercury cadmium telluride (MCT) alloys. The use of these alloys has, however, been faced with technological difficulties. One of the materials that have been tipped to be suitable to replace MCT is InAs/InxGa1-xSb strained layer superlattices (SLS’s). Atmospheric pressure metal-organic vapour phase epitaxy (MOVPE) has been used to grow InAs/GaSb strained layer superlattices (SLS’s) at 510 °C in this study. This is a starting point towards the development of MOVPE InAs/InxGa1-xSb SLS’s using the same system. Before the SLS’s could be attempted, the growth parameters for GaSb were optimised. Growth parameters for InAs were taken from reports on previous studies conducted using the same reactor. Initially, trimethylgallium, a source that has been used extensively in the same growth system for the growth of GaSb and InxGa1-xSb was intended to be used for gallium species. The high growth rates yielded by this source were too large for the growth of SLS structures, however. Thus, triethylgallium (rarely used for atmospheric pressure MOVPE) was utilized. GaSb layers (between 1 and 2 μm thick) were grown at two different temperatures (550 °C and 510 °C) with a varying V/III ratio. A V/III ratio of 1.5 was found to be optimal at 550 °C. However, the low incorporation efficiency of indium into GaSb at this temperature was inadequate to obtain InxGa1-xSb with an indium mole fraction (x) of around 0.3, which had previously been reported to be optimal for the performance of InAs/InxGa1-xSb SLS’s, due to the maximum splitting of the valence mini bands for this composition. The growth temperature was thus lowered to 510 °C. This resulted in an increase in the optimum V/III ratio to 1.75 for GaSb and yielded much higher incorporation efficiencies of indium in InxGa1-xSb. However, this lower growth temperature also produced poorer surface morphologies for both the binary and ternary layers, due to the reduced surface diffusion of the adsorbed species. An interface control study during the growth of InAs/GaSb SLS’s was subsequently conducted, by investigating the influence of different gas switching sequences on the interface type and quality. It was noted that the growth of SLS’s without any growth interruptions at the interfaces leads to tensile strained SLS’s (GaAs-like interfaces) with a rather large lattice mismatch. A 5 second flow of TMSb over the InAs surface and a flow of H2 over GaSb surface yielded compressively strained SLS’s. Flowing TMIn for 1 second and following by a flow of TMSb for 4 seconds over the GaSb surface, while flowing H2 for 5 seconds over the InAs surface, resulted in SLS’s with GaAs-like interfacial layers and a reduced lattice mismatch. Temperature gradients across the surface of the susceptor led to SLS’s with different structural quality. High resolution x-ray diffraction (HRXRD) was used to determine the thicknesses as well as the type of interfacial layers. The physical parameters of the SLS’s obtained from simulating the HRXRD spectra were comparable to the parameters obtained from cross sectional transmission electron microscopy (XTEM) images. The thicknesses of the layers and the interface type played a major role in determining the cut-off wavelength of the SLS’s.
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J, Boeckl John. "Microstructural investigation of defects in epitaxial GaAs grown on mismatched Ge and SiGe/Si substrates." Connect to this title online, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1116498970.
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Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xxii, 212 p.; also includes graphics. Includes bibliographical references (p. 203-212). Available online via OhioLINK's ETD Center
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Smith, Matthew T. "Design And Development Of A Silicon Carbide Chemical Vapor Deposition Reactor." [Tampa, Fla.] : University of South Florida, 2003. http://purl.fcla.edu/fcla/etd/SFE0000145.
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Ju, Wentao. "Experimental Investigation of the Epitaxial Lateral Overgrowth of Gallium Nitride and Simulation of Gallium Nitride Metalorganic Chemical Vapor Deposition Process." Ohio : Ohio University, 2003. http://www.ohiolink.edu/etd/view.cgi?ohiou1050589636.
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Aouadi, Mohamed-Samir. "Sputter-deposition of epitaxial CdTe and PbTe layers plasma emission spectroscopy of the discharge and photoluminescence spectroscopy of the layers." Thesis, University of Ottawa (Canada), 1989. http://hdl.handle.net/10393/5530.
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Yoo, Dongwon. "Growth and Characterization of III-Nitrides Materials System for Photonic and Electronic Devices by Metalorganic Chemical Vapor Deposition." Diss., Georgia Institute of Technology, 2007. http://hdl.handle.net/1853/16220.
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A wide variety of group III-Nitride-based photonic and electronic devices have opened a new era in the field of semiconductor research in the past ten years. The direct and large bandgap nature, intrinsic high carrier mobility, and the capability of forming heterostructures allow them to dominate photonic and electronic device market such as light emitters, photodiodes, or high-speed/high-power electronic devices. Avalanche photodiodes (APDs) based on group III-Nitrides materials are of interest due to potential capabilities for low dark current densities, high sensitivities and high optical gains in the ultraviolet (UV) spectral region. Wide-bandgap GaN-based APDs are excellent candidates for short-wavelength photodetectors because they have the capability for cut-off wavelengths in the UV spectral region (λ < 290 nm). These intrinsically solar-blind UV APDs will not require filters to operate in the solar-blind spectral regime of λ < 290 nm. For the growth of GaN-based heteroepitaxial layers on lattice-mismatched substrates, a high density of defects is usually introduced during the growth; thereby, causing a device failure by premature microplasma, which has been a major issue for GaN-based APDs. The extensive research on epitaxial growth and optimization of Alx Ga 1-x N (0 ≤ x ≤ 1) grown on low dislocation density native bulk III-N substrates have brought UV APDs into realization. GaN and AlGaN UV p-i-n APDs demonstrated first and record-high true avalanche gain of > 10,000 and 50, respectively. The large stable optical gains are attributed to the improved crystalline quality of epitaxial layers grown on low dislocation density bulk substrates. GaN p-i-n rectifiers have brought much research interest due to its superior physical properties. The AIN-free full-vertical GaN p-i-n rectifiers on n - type 6H-SiC substrates by employing a conducting AIGaN:Si buffer layer provides the advantages of the reduction of sidewall damage from plasma etching and lower forward resistance due to the reduction of current crowding at the bottom n -type layer. The AlGaN:Si nucleation layer was proven to provide excellent electrical properties while also acting as a good buffer role for subsequent GaN growth. The reverse breakdown voltage for a relatively thin 2.5 μm-thick i -region was found to be over -400V.
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Boeckl, John J. "Microstructural investigation of defects in epitaxial GaAs grown on mismatched Ge and SiGe/Si substrates." The Ohio State University, 2005. http://rave.ohiolink.edu/etdc/view?acc_num=osu1116498970.
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Gao, Yungeng. "Effect of fluid dynamics and reactor design on the epitaxial growth of gallium nitride on silicon substrate by metalorganic chemical vapor deposition." Ohio : Ohio University, 2000. http://www.ohiolink.edu/etd/view.cgi?ohiou1179171265.
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Thelander, Erik [Verfasser], Bernd [Akademischer Betreuer] Rauschenbach, Bernd [Gutachter] Rauschenbach, and Hans-Ulrich [Gutachter] Krebs. "Epitaxial Ge-Sb-Te Thin Films by Pulsed Laser Deposition / Erik Thelander ; Gutachter: Bernd Rauschenbach, Hans-Ulrich Krebs ; Betreuer: Bernd Rauschenbach." Leipzig : Universitätsbibliothek Leipzig, 2015. http://d-nb.info/1239565011/34.
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Kwon, Ah-Ram. "Epitaxial Nd-Fe-B films: Growth, texture, magnetism and the influence of mechanical elongation." Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2010. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-23750.
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The work in this thesis focuses on the preparation of epitaxial Nd-Fe-B thin films using pulsed laser deposition for good hard magnetic properties. They are suitable for a basic understanding of the intrinsic magnetic properties. Compositional control was necessary to achieve phase formation with improved magnetic properties. Nd-Fe-B samples were prepared on single crystal MgO (001) substrates with different buffer layers in order to obtain good textures with different surface morphology. The smooth and continuous epitaxial films were suitable for performing magnetization measurements under stress. Although the magnetostriction is easily neglected in the Nd2Fe14B compound, distinguishable inverse magnetostriction was observed by conventional tensile elongation with a flexible substrate. As a result, anisotropic strain in the film, which breaks the in-plane symmetry, affected the opening angle during the spin reorientation. Therefore an elliptical distortion of the in-plane anisotropy below the spin reorientation temperature of Nd2Fe14B was obtained, whereas the transition temperature itself was not influenced significantlyDiese Arbeit behandelt die Herstellung dünner epitaktischer Nd-Fe-B-Schichten mit gepulster Laserdeposition mit dem Ziel, gute hartmagnetische Eigenschaften zu erreichen. Diese Schichten sind außerdem für das Verständnis grundlegender magnetischer Eigenschaften geeignet. Die Kontrolle der Zusammensetzung ist notwendig, um die Phasenbildung und optimale hartmagnetische Eigenschaften zu erreichen. Nd-Fe-B-Schichten wurden auf einkristallinen MgO (001)-Substraten mit verschiedenen Buffern deponiert, um unterschiedliche Texturen und Oberflächenmorphologien einzustellen. Die glatten kontinuierlichen epitaktischen Schichten ermöglichen die Messung der Magnetisierung bei gleichzeitig angelegter mechanischer Spannung. Obwohl die Magnetostriktion bei Nd-Fe-B im Allgemeinen vernachlässigt werden kann, konnte an Nd-Fe-B-Schichten nach dem Aufbringen einer Dehnung auf ein flexibles Substrat eine deutliche inverse Magnetostriktion induziert werden. Die anisotrope Dehnung in der Schicht, die die Symmetrie in der Schichtebene bricht, beeinflusst die Öffnungswinkel bei der Spinreorientierung. Damit wurde unterhalb der Spinreorientierungstemperatur eine elliptische Verzerrung der Anisotropie in der Schichtebene erreicht, die Übergangstemperatur selbst änderte sich dagegen nicht signifikant
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Maneshian, Mohammad Hassan. "The Influence of Ohmic Metals and Oxide Deposition on the Structure and Electrical Properties of Multilayer Epitaxial Graphene on Silicon Carbide Substrates." Thesis, University of North Texas, 2011. https://digital.library.unt.edu/ark:/67531/metadc68009/.
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Graphene has attracted significant research attention for next generation of semiconductor devices due to its high electron mobility and compatibility with planar semiconductor processing. In this dissertation, the influences of Ohmic metals and high dielectric (high-k) constant aluminum oxide (Al2O3) deposition on the structural and electrical properties of multi-layer epitaxial graphene (MLG) grown by graphitization of silicon carbide (SiC) substrates have been investigated. Uniform MLG was successfully grown by sublimation of silicon from epitaxy-ready, Si and C terminated, 6H-SiC wafers in high-vacuum and argon atmosphere. The graphene formation was accompanied by a significant enhancement of Ohmic behavior, and, was found to be sensitive to the temperature ramp-up rate and annealing time. High-resolution transmission electron microscopy (HRTEM) showed that the interface between the metal and SiC remained sharp and free of macroscopic defects even after 30 min, 1430 °C anneals. The impact of high dielectric constant Al2O3 and its deposition by radio frequency (RF) magnetron sputtering on the structural and electrical properties of MLG is discussed. HRTEM analysis confirms that the Al2O3/MLG interface is relatively sharp and that thickness approximation of the MLG using angle resolved X-ray photoelectron spectroscopy (ARXPS) as well as variable-angle spectroscopic ellipsometry (VASE) is accurate. The totality of results indicate that ARXPS can be used as a nondestructive tool to measure the thickness of MLG, and that RF sputtered Al2O3 can be used as a (high-k) constant gate oxide in multilayer grapheme based transistor applications.
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Kwon, Ah-Ram. "Epitaxial Nd-Fe-B films: Growth, texture, magnetism and the influence of mechanical elongation." Doctoral thesis, Technische Universität Dresden, 2008. https://tud.qucosa.de/id/qucosa%3A25084.
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The work in this thesis focuses on the preparation of epitaxial Nd-Fe-B thin films using pulsed laser deposition for good hard magnetic properties. They are suitable for a basic understanding of the intrinsic magnetic properties. Compositional control was necessary to achieve phase formation with improved magnetic properties. Nd-Fe-B samples were prepared on single crystal MgO (001) substrates with different buffer layers in order to obtain good textures with different surface morphology. The smooth and continuous epitaxial films were suitable for performing magnetization measurements under stress. Although the magnetostriction is easily neglected in the Nd2Fe14B compound, distinguishable inverse magnetostriction was observed by conventional tensile elongation with a flexible substrate. As a result, anisotropic strain in the film, which breaks the in-plane symmetry, affected the opening angle during the spin reorientation. Therefore an elliptical distortion of the in-plane anisotropy below the spin reorientation temperature of Nd2Fe14B was obtained, whereas the transition temperature itself was not influenced significantly.Diese Arbeit behandelt die Herstellung dünner epitaktischer Nd-Fe-B-Schichten mit gepulster Laserdeposition mit dem Ziel, gute hartmagnetische Eigenschaften zu erreichen. Diese Schichten sind außerdem für das Verständnis grundlegender magnetischer Eigenschaften geeignet. Die Kontrolle der Zusammensetzung ist notwendig, um die Phasenbildung und optimale hartmagnetische Eigenschaften zu erreichen. Nd-Fe-B-Schichten wurden auf einkristallinen MgO (001)-Substraten mit verschiedenen Buffern deponiert, um unterschiedliche Texturen und Oberflächenmorphologien einzustellen. Die glatten kontinuierlichen epitaktischen Schichten ermöglichen die Messung der Magnetisierung bei gleichzeitig angelegter mechanischer Spannung. Obwohl die Magnetostriktion bei Nd-Fe-B im Allgemeinen vernachlässigt werden kann, konnte an Nd-Fe-B-Schichten nach dem Aufbringen einer Dehnung auf ein flexibles Substrat eine deutliche inverse Magnetostriktion induziert werden. Die anisotrope Dehnung in der Schicht, die die Symmetrie in der Schichtebene bricht, beeinflusst die Öffnungswinkel bei der Spinreorientierung. Damit wurde unterhalb der Spinreorientierungstemperatur eine elliptische Verzerrung der Anisotropie in der Schichtebene erreicht, die Übergangstemperatur selbst änderte sich dagegen nicht signifikant.
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Wu, Kuan-Ting. "Layered Ruddlesden-Popper Lan+1NinO3n+1 (n = 1, 2 and 3) epitaxial films grown by pulsed laser deposition for potential fuel cell applications." Thesis, Imperial College London, 2014. http://hdl.handle.net/10044/1/23297.
Full textAbstract:
Layered Ruddlesden-Popper (RP) type La_n+1Ni_nO_{3n+1} (n = 1, 2 and 3) oxides have recently been suggested as candidates for solid oxide fuel cell (SOFC) cathodes. However, the transport properties of the higher order (n = 2 and 3) phases have not been well-understood. The aim of this work is to achieve well-defined epitaxial La_3Ni_2O_{7-δ} and La_4Ni_3O_{10-δ} films deposited by the pulsed laser deposition (PLD) technique in order to fundamentally investigate their intrinsic anisotropic properties for SOFC applications. This research involved PLD target synthesis and PLD deposition for these RP materials. The obtained films were evaluated through crystallographic, compositional, surface morphological and microstructural characterisation. Their electrical, oxygen diffusion and surface exchange properties were characterised by 4-point DC van der Pauw and the isotopic exchange depth profile (IEDP) with secondary ion mass spectrometry (SIMS) method. Finally, the surface and interface information were also obtained via SIMS and low energy ion scattering (LEIS) techniques. An effect of target degradation during deposition was found to have significant influence on the microstructural and compositional variation with increasing film thickness. Successful epitaxial growth of the higher order phases (n = 2 and 3) of lanthanum nickelate have been demonstrated by PLD for the first time. The total planar electrical conductivity of these higher order RP epitaxial films exhibits a more promising conductivity value than La_2NiO_{4+δ}. These dense higher order RP epitaxial films enabled the first information about the oxygen diffusion and surface exchange properties along the c-axis to be obtained. Also, an outermost surface structure of LaO-termination, followed by a Ni-enrichment in the sub-surface region for these RP materials was found by LEIS analysis. These studies provide useful information to help the further development of these materials and related RP-phases for the potential SOFC applications in the future.
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Lyu, Jike. "Epitaxial Ferroelectric Thin Films on Si(001): strain tuning of BaTiO3 and stabilization of polar phase in Hf0.5Zr0.5O2." Doctoral thesis, Universitat Autònoma de Barcelona, 2019. http://hdl.handle.net/10803/667989.
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Choi, Suk. "Growth and characterization of III-nitride materials for high efficiency optoelectronic devices by metalorganic chemical vapor deposition." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45823.
Full textAbstract:
Efficiency droop is a critical issue for the Group III-nitride based light-emitting diodes (LEDs) to be competitive in the general lighting application. Carrier spill-over have been suggested as an origin of the efficiency droop, and an InAlN electron-blocking layer (EBL) is suggested as a replacement of the conventional AlGaN EBL for improved performance of LED. Optimum growth condition of InAlN layer was developed, and high quality InAlN layer was grown by using metalorganic chemical vapor deposition (MOCVD). A LED structure employing an InAlN EBL was grown and its efficiency droop performance was compared with a LED with an AlGaN EBL. Characterization results suggested that the InAlN EBL delivers more effective electron blocking over AlGaN EBL. Hole-injection performance of the InAlN EBL was examined by growing and testing a series of LEDs with different InAlN EBL thickness. Analysis results by using extended quantum efficiency model shows that further improvement in the performance of LED requires better hole-injection performance of the InAlN EBL. Advanced EBL structures such as strain-engineered InAlN EBL and compositionally-graded InAlN EBLs for the delivery of higher hole-injection efficiency were also grown and tested.
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Mukherjee, Devajyoti. "Growth and Characterization of Epitaxial Thin Films and Multiferroic Heterostructures of Ferromagnetic and Ferroelectric Materials." Scholar Commons, 2010. http://scholarcommons.usf.edu/etd/3622.
Full textAbstract:
Multiferroic materials exhibit unique properties such as simultaneous existence of
two or more of coupled ferroic order parameters (ferromagnetism, ferroelectricity,
ferroelasticity or their anti-ferroic counterparts) in a single material. Recent years have
seen a huge research interest in multiferroic materials for their potential application as
high density non-volatile memory devices. However, the scarcity of these materials in
single phase and the weak coupling of their ferroic components have directed the
research towards multiferroic heterostructures. These systems operate by coupling the
magnetic and electric properties of two materials, generally a ferromagnetic material and
a ferroelectric material via strain. In this work, horizontal heterostructures of composite
multiferroic materials were grown and characterized using pulsed laser ablation technique.
Alternate magnetic and ferroelectric layers of cobalt ferrite and lead zirconium titanate,
respectively, were fabricated and the coupling effect was studied by X-ray stress analysis.
It was observed that the interfacial stress played an important role in the coupling effect
between the phases. Doped zinc oxide (ZnO) heterostructures were also studied where
the ferromagnetic phase was a layer of manganese doped ZnO and the ferroelectric phase
was a layer of vanadium doped ZnO. For the first time, a clear evidence of possible room
temperature magneto-elastic coupling was observed in these heterostructures. This work
provides new insight into the stress mediated coupling mechanisms in composite
multiferroics.
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Weng, Xiaorong. "Epitaxial CoxNi1-x nanowires in SrTiO3 matrix : growth, structure and control of magnetic anisotropy." Electronic Thesis or Diss., Sorbonne université, 2019. http://www.theses.fr/2019SORUS418.
Full textAbstract:
Cette thèse décrit l’étude de l’auto-assemblage de nanofils ferromagnétiques de CoxNi1-x épitaxiés dans une matrice de SrTiO3. Ce système est elaboré par ablation laser pulsé. Profitant du dépôt séquentiel des fils et de la matrice, le diamètre des nanofils est contrôlé dans la gamme de 1,7 à 5,3 nm. En raison du désaccord de paramètre de maille entre les fils et la matrice, les nanofils sont dilatés axialement. Cette déformation décroît lorsque le diamètre des fils augmente, dans la gamme de 2-4%. L'anisotropie magnétique des nanofils résulte de la compétition des anisotropies magnétostatique et magnétoélastique. L'effet magnétostatique favorise un axe d'aimantation facile le long de l'axe des fils. La contribution magnétoélastique introduite par la déformation dépend de la constante de magnétostriction et de la déformation. Elle est uniaxiale, négative pour Ni et positive pour une concentration de Co d'environ 20% et plus. Sous une déformation supérieure à 0,8%, l’anisotropie magnétoélastique prédomine, faisant de l’axe des fils un axe d'aimantation dur pour Ni. Pour les nanofils de CoNi, la grande déformation renforce le caractère facile de l’axe des fils. Il en résulte une augmentation de la température de blocage par rapport à la température ambiante, indiquant une augmentation de la stabilité thermique de l'aimantation. Une étude spectroscopique des moments magnétiques de spin et d'orbite met en évidence le fait que l'anisotropie du moment orbital peut être corrélée à l'anisotropie magnétoélastique. Le contrôle de l'anisotropie magnétique par la déformation ou le diamètre est un bon point de départ pour la construction de structures nanomagnétiques 3DThis thesis describes the study of self-assembled epitaxial ferromagnetic CoxNi1-x nanowires in SrTiO3 matrix. This system is grown by pulsed laser deposition. Taking advantage of the sequential deposition of wires and matrix, the diameter of nanowires is controlled in the 1.7-5.3 nm range. Due to the lattice mismatch between wires and matrix, nanowires are in tensile axial strain. The strain decreases with increasing diameter and is in the 2-4% range. Large strain is thus achieved in this vertically aligned nanocomposite structure. The total magnetic anisotropy of the nanowires reflects the competition of the magnetostatic and magnetoelastic anisotropies. The magnetostatic effect favors an easy magnetization axis along the wire axis. The magnetoelastic contribution introduced by the tensile strain depends on the magnetostriction constant and the strain. It is uniaxial, negative for Ni and positive for Co concentration of about 20% and above. Under a strain larger than 0.8%, the magnetoelastic anisotropy dominates in magnitude the magnetostatic one, leading the wire axis to be a hard magnetization axis for Ni. For CoNi alloy nanowires, the large strain reinforces the easy character of the wire axis. This results in the enhancement of the blocking temperature over room temperature, indicating the increased thermal stability of magnetization. A spectroscopic study of the spin and orbital magnetic moments evidences the fact that the anisotropy of the orbital moment can be correlated with the magnetoelastic anisotropy. The control of the magnetic anisotropy by the strain or the diameter is a good starting point for the construction of 3D nanomagnetic structures
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Liu, Pei-Yi, and 劉佩宜. "Reactive Deposition of Epitaxial Cobalt Disilicide." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/30953331759563804551.
Full textAbstract:
碩士國立清華大學
材料科學工程學系
98
The relatively small lattice mismatch (~ 1.2 %) between CoSi2 and Si and the similarity in crystal structure allow the possibility of growing epitaxial CoSi2 layer on Si. Therefore CoSi2 has a great advantage to be used in semiconductor technology. There are several reported methods in controlling the formation process of epitaxial CoSi2 on Si. And each method has various experimental factors to form different CoSi2 structures. In order to make a systematic understanding on the effect of each experimental factor on the growth of cobalt silicides, nominal thicknesses of cobalt, deposition rates and growth temperatures were changed separately in this thesis. The effect of nominal thickness of Co layers on the growth of the epitaxial CoSi2 islands using reactive deposition epitaxy was investigated. It was found that the nucleation density of CoSi2 and the average size of CoSi2 islands increase with increasing the nominal thickness of the Co layers from 0.3 nm to 0.5 nm. As the average size of CoSi2 islands increases, the distribution range of width and length of the CoSi2 islands become larger as well. In addition, CoSi2 islands containing both the A-type interfaces and the B-type interfaces coexisted and nucleated independently during growth. The number of B-type (twinned) interfaces is much greater than that of the A-type (untwinned) interfaces. It was found that, as the deposition rate increases (0.003 nm/sec – 0.005 nm/sec), the average length of CoSi2 islands is shorter but the distribution range of the width is the same. So the distribution range of width is independent on the deposition rate. Besides, the nucleation density of CoSi2 islands increases dramatically with increasing the deposition rate until it is close to the saturation. Moreover, the percentage of the B-type interfaces is higher with increasing deposition rate as well. It was found that, as the substrate temperature increased from 750 ℃ to 820 ℃, the average size and the aspect ratio of CoSi2 islands were larger and the nucleation density decreased.
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Mei-ChingHuang and 黃美靜. "RF magnetron sputter deposition of BiCuSeO epitaxial films." Thesis, 2018. http://ndltd.ncl.edu.tw/handle/sxa5ep.
Full textAbstract:
碩士國立成功大學
材料科學及工程學系
106
In this study, we attempted to grow epitaxial BiCuSeO (BCSO) films on (110) and (001) SrTiO3 (STO) substrates as the bottom electrode for the growth of multiferroic BiFeO3 (BFO) films. In our previous attempts, BCSO films of two in-plane orientations were obtained owing to the rapid deposition rate. So, in this work, we used two methods to reduce the rate. One was placing a stainless steel mesh above the substrate in order to scatter the sputtered atoms. Another one was controlling shutter opening time to adjust deposition rate. The films grown with the mesh were mainly (001) orientated but contained some (110) orientation and yet the film surface was rough. The films grown with the shutter had a unique (001) texture when the substrate temperature was 400 C and the shutter opening and closing times were 1 and 30 seconds, respectively. High-resolution X-ray diffraction (HRXRD) confirmed that the (001) oriented films were in-plane aligned as well, i.e. the grown BCSO films were epitaxial. Although bulk BCSO had larger a/b axes than STO, HRXRD showed that the a/b axes of BCSO films were stretched rather than compressed. Similarly, the c-axis of films was slightly shortened instead of being elongated. This was probably related to oxygen deficiency in the films. Cross-sectional transmission electron microscopy confirmed the epitaxial relationship between BCSO film and STO substrate. The resistivity of films measured at room temperature was 2.02×10-2 Ohmcm, which was good enough as the electrode. It was found that (001) BCSO epitaxial films could also be grown on the (110) oriented STO substrates. The BCSO films on (110) STO could be grown at very high rate, but only at the substrate temperature of 500 C. The resistivity of the BCSO epitaxial films on (110) STO was higher (9.55×10-3 Ohmcm). Preliminary attempts were made to grow epitaxial BFO films on BCSO. Polycrystalline BFO films of a pure phase were obtained, but the epitaxial growth has yet to be achieved.
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Thelander, Erik. "Epitaxial Ge-Sb-Te Thin Films by Pulsed Laser Deposition." Doctoral thesis, 2014. https://ul.qucosa.de/id/qucosa%3A13245.
Full textAbstract:
This thesis deals with the synthesis and characterization of Ge-Te-Sb (GST) thin films. The films were deposited using a Pulsed Laser Deposition (PLD) method and mainly characterized with XRD, SEM, AFM and TEM.
For amorphous and polycrystalline films, un-etched Si(100) was used. The amorphous films showed a similar crystallization behavior as films deposited with sputtering and evaporation techniques.
When depositing GST on un-etched Si(100) substrates at elevated substrate temperatures (130-240°C), polycrystalline but highly textured films were obtained. The preferred growth orientation was either GST(111) or GST(0001) depending on if the films were cubic or hexagonal.
Epitaxial films were prepared on crystalline substrates. On KCl(100), a mixed growth of hexagonal GST(0001) and cubic GST(100) was observed. The hexagonal phase dominates at low temperatures whereas the cubic phase dominates at high temperatures. The cubic phase is accompanied with a presumed GST(221) orientation when the film thickness exceeds ~70 nm. Epitaxial films were obtained with deposition rates as high as 250 nm/min.
On BaF2(111), only (0001) oriented epitaxial hexagonal GST films are found, independent of substrate temperature, frequency or deposition background pressure. At high substrate temperatures there is a loss of Ge and Te which shifts the crystalline phase from Ge2Sb2Te5 towards GeSb2Te4. GST films deposited at room temperature on BaF2(111) were in an amorphous state, but after exposure to an annealing treatment they crystallize in an epitaxial cubic structure.
Film deposition on pre-cleaned and buffered ammonium fluoride etched Si(111) show growth of epitaxial hexagonal GST, similar to that of the deposition on BaF2(111). When the Si-substrates were heated directly to the deposition temperature films of high crystal-line quality were obtained. An additional heat treatment of the Si-substrates prior to deposition deteriorated the crystal quality severely.
The gained results show that PLD can be used as a method in order to obtain high quality epitaxial Ge-Sb-Te films from a compound target and using high deposition rates.
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Wang, Cheng-Kuo, and 王鎮國. "Process Optimization of CVD Epitaxial Deposition Using Modified Genetic Algorithms." Thesis, 1997. http://ndltd.ncl.edu.tw/handle/97649431188973815481.
Full textAbstract:
碩士國立交通大學
控制工程系
85
A vertical chemical vapor deposition process (CVD) optimization method using modified geneticalgorithms (MGA) has been proposed. Genetic algorithms (GA) are a computational optimization paradigm modeled after biological evolution concept. Strategies such as: elitist with ranking selection reproduction scheme and multiple points crossover are used to raise the search efficiency of the traditional GA. Self-adjusted operator probability not only helps to avoid premature but also define parameters automatically. Moreover, we integrate hybrid genetic operator, immigration operator, and heuristic fitness function to enhance its local fine tuning ability. In order to prove the improvement results, we initially optimize several highly nonlinear functions with MGA, then, with a well-defined fitness function, the optimization procedure has been successfully applied to the CVD process with various noise level. Through the optimal solution, we obtained the thickness in deposition layers which is more uniformly distributed over the wafers. These results demonstrate the superiority of the proposed optimization solution in comparison with other existing optimization algorithms.
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Hsiang, Chen-chih, and 項承智. "Epitaxial growth of ZnO by microwave-assisted chemical bath deposition." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/w9pmt8.
Full textAbstract:
碩士國立交通大學
材料科學與工程學系所
106
Microwave-assisted chemical bath deposition (MWCBD) is a newly developed method for rapid synthesis of single-crystalline ZnO nanorods. In this study, MWCBD was used to synthesize ZnO with high-quality epitaxial ZnO film, using hexahydrate zinc nitrate (Zn(NO3)2∙6H2O) as the Zn2+ source, hexamethylenetetramine (HMT, C6H12N4) as pH buffer, GaN/sapphire as the substrate with small lattice mismatch with ZnO, at temperature less than 100°C. Also, the effect of sodium citrate (Na3C6H5O7) as the capping agent on lateral growth of ZnO rod for continuous film formation has been explored based on the evolution of the measured aspect ratio of height-to-width in the microwave environment. Additionally, the effects of temperature, concentration, and time on pH change of aqueous solutions with precipitation of ZnO powders and during microwave heating were evaluated. When the heating temperature is increased, the color of the aqueous solution as seen from the visual appearance becomes more pure white as more precipitated ZnO powders were produced and the pH value decreases from 6.8 to about 5.5. Increasing the concentration of zinc nitrate precursor results in the higher quantity of ZnO powders and reduction of the pH value of the aqueous solution. In the study of ZnO epitaxy on GaN, scanning electron microscopy observations in top view and cross-section show that thin film of epitaxial ZnO in thickness of about 1 μm can be effectively grown on GaN/sapphire with MWCBD by adding sodium citrate to the solution to enhance the lateral growth of ZnO rods with coalescence. It is found that to reach an aspect ratio of height to width of 0.83, the concentration of sodium citrate is required to increase to 0.04 mM which can still have an average growth rate of ~ 1 m/h. The film quality as characterized by x-ray diffraction in –scan shows a full width at half maximum of the (0004) rocking curve in 860 arcsec, which is twice as high as substrate of GaN, whereas it is 1288 arcsec for (303 ̅2) FWHM slightly increased from 1078 arcsec for GaN, suggesting that ZnO film quality is mainly affected by screw dislocations formed in rod nucleation.
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謝明燈. "Low temperature silicon epitaxial growth by plasma enhanced chemical vapor deposition." Thesis, 1993. http://ndltd.ncl.edu.tw/handle/52684092564705128377.
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