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Liu, Yujia, Kevin-Peter Gradwohl, Chenhsun Lu, Yuji Yamamoto, Thilo Remmele, Cedric Corley-Wiciak, Thomas Teubner, Carsten Richter, Martin Albrecht i Torsten Boeck. "Viewing SiGe Heterostructure for Qubits with Dislocation Theory". ECS Transactions 109, nr 4 (30.09.2022): 189–96. http://dx.doi.org/10.1149/10904.0189ecst.
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Strained isotopically enriched 28Si strained layers in SiGe/Si/SiGe heterostrustructures is an excellent material platform for electron spin qubits. In this work, we report the fabrication of 28SiGe/28Si/28SiGe heterostructures for qubit devices by a hybrid MBE/CVD growth, where the thick relaxed SiGe buffer is realized by a reduced-pressure CVD and the 28SiGe/28Si/28SiGe stack is grown by an MBE. Here, we achieve a fully strained 28Si layer in such heterostructure with a 29Si concentration as low as 200 ppm within the MBE grown layers. It was possible to conclude that 29Si primarily originates from the residual natural Si vapour in the MBE chamber. Furthermore, we also present our studies about the growth temperature effect on the misfit dislocation formation in this heterostructure. It was possible to show that at a low MBE growth temperature, such as 350°C, the misfit dislocation formation is significantly suppressed.
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Zhang, Liyao, Yuxin Song, Nils von den Driesch, Zhenpu Zhang, Dan Buca, Detlev Grützmacher i Shumin Wang. "Structural Property Study for GeSn Thin Films". Materials 13, nr 16 (17.08.2020): 3645. http://dx.doi.org/10.3390/ma13163645.
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The structural properties of GeSn thin films with different Sn concentrations and thicknesses grown on Ge (001) by molecular beam epitaxy (MBE) and on Ge-buffered Si (001) wafers by chemical vapor deposition (CVD) were analyzed through high resolution X-ray diffraction and cross-sectional transmission electron microscopy. Two-dimensional reciprocal space maps around the asymmetric (224) reflection were collected by X-ray diffraction for both the whole structures and the GeSn epilayers. The broadenings of the features of the GeSn epilayers with different relaxations in the ω direction, along the ω-2θ direction and parallel to the surface were investigated. The dislocations were identified by transmission electron microscopy. Threading dislocations were found in MBE grown GeSn layers, but not in the CVD grown ones. The point defects and dislocations were two possible reasons for the poor optical properties in the GeSn alloys grown by MBE.
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Moustakas, Theodore D. "Molecular Beam Epitaxy: Thin Film Growth and Surface Studies". MRS Bulletin 13, nr 11 (listopad 1988): 29–36. http://dx.doi.org/10.1557/s0883769400063892.
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Molecular Beam Epitaxy (MBE) is a thin film deposition process in which thermal beams of atoms or molecules react on the clean surface of a single-crystalline substrate, held at high temperatures under ultrahigh vacuum conditions, to form an epitaxial film. Thus, contrary to the CVD processes described in the other articles, the MBE process is a physical method of thin film deposition.The vacuum requirements for the MBE process are typically better than 10−10torr. This makes it possible to grow epitaxial films with high purity and excellent crystal quality at relatively low substrate temperatures. Additionally, the ultrahigh vacuum environment allows the study of surface, interface, and bulk properties of the growing film in real time, by employing a variety of structural and analytical probes.Although the MBE deposition process was first proposed by Günther in 1958, its implementation had to wait for the development of the ultrahigh vacuum technology. In 1968 Davey and Pankey successfully grew epitaxial GaAs films by the MBE process. At the same time Arthur's work on the kinetics of GaAs growth laid the groundwork for the growth of high quality MBE films of GaAs and other III-V compounds by Arthur and LePore and Cho.
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van Wingerden, J., R. H. van Aken, Y. A. Wiechers, P. M. L. O. Scholte i F. Tuinstra. "Growth pyramids on Si(111) facets: A CVD and MBE study". Physical Review B 57, nr 12 (15.03.1998): 7252–58. http://dx.doi.org/10.1103/physrevb.57.7252.
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O`Raifeartaigh, C., L. Bradley, R. C. Barklie, A. M. Hodge i E. D. Richmond. "Spin-dependent photoconductivity in CVD- and MBE-grown silicon-on-sapphire". Semiconductor Science and Technology 10, nr 12 (1.12.1995): 1595–603. http://dx.doi.org/10.1088/0268-1242/10/12/007.
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Miao, Yuanhao, Guilei Wang, Zhenzhen Kong, Buqing Xu, Xuewei Zhao, Xue Luo, Hongxiao Lin i in. "Review of Si-Based GeSn CVD Growth and Optoelectronic Applications". Nanomaterials 11, nr 10 (29.09.2021): 2556. http://dx.doi.org/10.3390/nano11102556.
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GeSn alloys have already attracted extensive attention due to their excellent properties and wide-ranging electronic and optoelectronic applications. Both theoretical and experimental results have shown that direct bandgap GeSn alloys are preferable for Si-based, high-efficiency light source applications. For the abovementioned purposes, molecular beam epitaxy (MBE), physical vapour deposition (PVD), and chemical vapor deposition (CVD) technologies have been extensively explored to grow high-quality GeSn alloys. However, CVD is the dominant growth method in the industry, and it is therefore more easily transferred. This review is focused on the recent progress in GeSn CVD growth (including ion implantation, in situ doping technology, and ohmic contacts), GeSn detectors, GeSn lasers, and GeSn transistors. These review results will provide huge advancements for the research and development of high-performance electronic and optoelectronic devices.
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Ermolaev, Georgy A., Marwa A. El-Sayed, Dmitry I. Yakubovsky, Kirill V. Voronin, Roman I. Romanov, Mikhail K. Tatmyshevskiy, Natalia V. Doroshina i in. "Optical Constants and Structural Properties of Epitaxial MoS2 Monolayers". Nanomaterials 11, nr 6 (27.05.2021): 1411. http://dx.doi.org/10.3390/nano11061411.
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Two-dimensional layers of transition-metal dichalcogenides (TMDs) have been widely studied owing to their exciting potential for applications in advanced electronic and optoelectronic devices. Typically, monolayers of TMDs are produced either by mechanical exfoliation or chemical vapor deposition (CVD). While the former produces high-quality flakes with a size limited to a few micrometers, the latter gives large-area layers but with a nonuniform surface resulting from multiple defects and randomly oriented domains. The use of epitaxy growth can produce continuous, crystalline and uniform films with fewer defects. Here, we present a comprehensive study of the optical and structural properties of a single layer of MoS2 synthesized by molecular beam epitaxy (MBE) on a sapphire substrate. For optical characterization, we performed spectroscopic ellipsometry over a broad spectral range (from 250 to 1700 nm) under variable incident angles. The structural quality was assessed by optical microscopy, atomic force microscopy, scanning electron microscopy, and Raman spectroscopy through which we were able to confirm that our sample contains a single-atomic layer of MoS2 with a low number of defects. Raman and photoluminescence spectroscopies revealed that MBE-synthesized MoS2 layers exhibit a two-times higher quantum yield of photoluminescence along with lower photobleaching compared to CVD-grown MoS2, thus making it an attractive candidate for photonic applications.
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Chen, R. S., H. Y. Tsai, C. H. Chan, Y. S. Huang, Y. T. Chen, K. H. Chen i L. C. Chen. "Comparison of CVD- and MBE-grown GaN Nanowires: Crystallinity, Photoluminescence, and Photoconductivity". Journal of Electronic Materials 44, nr 1 (25.10.2014): 177–87. http://dx.doi.org/10.1007/s11664-014-3457-y.
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Yoshikawa, A., T. Okamoto, H. Yasuda, S. Yamaga i H. Kasai. "“MBE-Like” and “CVD-like” atomic layer epitaxy of ZnSe in mombe system". Journal of Crystal Growth 101, nr 1-4 (kwiecień 1990): 86–90. http://dx.doi.org/10.1016/0022-0248(90)90942-e.
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Werner, P. "Growth and Properties of Silicon Nanowires for Low-Dimensional Devices". Solid State Phenomena 131-133 (październik 2007): 535–40. http://dx.doi.org/10.4028/www.scientific.net/ssp.131-133.535.
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The generation of semiconductor nanowires (NWs) by a “bottom-up” approach is of technological interest for the development of new nanodevices. In most cases Si and SiGe nanowires (NWs) are grown by molecular beam epitaxy (MBE) and by chemical vapor deposition (CVD) on the base of the vapor-liquid-solid-mechanism (VLS). In both cases small metal droplets act as a seed for the NW formation. The article mainly refers to the specific features of the MBE growth. The application of metals related to the VLS growth concept (quite often gold droplets are used) also causes several disadvantages of this approach, e.g., the formation of a metal wetting layer on all surfaces, dislocations, and electric active point defects. Concerning the formation of devices, technological steps, such as oxidation and doping of NWs, have to be considered. Specific techniques have to be applied to investigate the properties of individual semiconductor NWs. Some examples shall illustrate this topic.
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Nastovjak, Alla G., Igor G. Neizvestny i Nataliya L. Shwartz. "Possibilities of Monte Carlo simulation for examination of nanowhisker growth". Pure and Applied Chemistry 82, nr 11 (2.08.2010): 2017–25. http://dx.doi.org/10.1351/pac-con-09-12-03.
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The kinetic Monte Carlo (MC) model of nanowhisker (NW) growth is suggested. Two variants of growth are possible in the model—molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). The effect of deposition conditions and growth regimes on the whisker morphology was examined within the framework of the vapor–liquid–solid (VLS) mechanism. A range of model growth conditions corresponding to NW and nanotube formation was determined. The suggested MC model was used for analyses of the morphology of the catalyst–whisker interface and for examination of Si–Ge whisker growth.
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Qi, Dongfeng, Hanhui Liu, Donglin Huang, Letian Wang, Songyan Chen i Costas P. Grigoropoulos. "High-quality strain-relaxed Si0.72Ge0.28 layers grown by MBE-UHV/CVD combined deposition chamber". Journal of Alloys and Compounds 735 (luty 2018): 588–93. http://dx.doi.org/10.1016/j.jallcom.2017.11.105.
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Schroeder, T., A. Giussani, H. J. Muessig, G. Weidner, I. Costina, Ch Wenger, M. Lukosius, P. Storck i P. Zaumseil. "Ge integration on Si via rare earth oxide buffers: From MBE to CVD (Invited Paper)". Microelectronic Engineering 86, nr 7-9 (lipiec 2009): 1615–20. http://dx.doi.org/10.1016/j.mee.2009.03.108.
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Leifeld, O., B. Müller, D. A. Grützmacher i K. Kern. "A UHV STM for in situ characterization of MBE/CVD growth on 4-inch wafers". Applied Physics A: Materials Science & Processing 66, nr 7 (1.03.1998): S993—S997. http://dx.doi.org/10.1007/s003390051282.
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Uchida, M., M. Deguchi, Kazuhiko Takahashi, Makoto Kitabatake i M. Kitagawa. "Heteroepitaxial Growth of 3C-SiC on Surface-Structure-Controlled MBE Layer by Low-Pressure CVD". Materials Science Forum 264-268 (luty 1998): 243–46. http://dx.doi.org/10.4028/www.scientific.net/msf.264-268.243.
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Claflin, B., A. Kiefer, R. Beeler, Z. Q. Fang i G. Grzybowski. "Characterization of Ge1-x-ySixSny Ternary Alloys - Comparison of UHV-CVD and Gas Source MBE Growth". ECS Transactions 64, nr 6 (12.08.2014): 801–10. http://dx.doi.org/10.1149/06406.0801ecst.
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Guy, Owen J., Amador Pérez-Tomás, Michael R. Jennings, Michal Lodzinski, A. Castaing, Philip A. Mawby, James A. Covington i in. "Investigation of Si/4H-SiC Hetero-Junction Growth and Electrical Properties". Materials Science Forum 615-617 (marzec 2009): 443–46. http://dx.doi.org/10.4028/www.scientific.net/msf.615-617.443.
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This paper describes the growth and characterisation of Si/SiC heterojunction structures. Heterojunction structures are of interest for low on-resistance diodes and as potential solutions to fabricating SiC MOS devices with lower interface state densities. The formation of the Si/SiC heterojunction using Chemical Vapour Deposition (CVD), Molecular Beam Epitaxy (MBE), Electron Beam Evaporation under UHV conditions (EBE-UHV) and Layer Transfer (LT) are reported. The physical nature of Si/SiC structures has been investigated using scanning electron microscopy (SEM). Results of electrical characterisation of the Si/SiC heterojunctions, are also reported. Finally, thermal oxidation of a Si / SiC heterojunction structures has been performed. The C(V) characteristics of the resulting oxides are compared to conventional thermal oxides on SiC.
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N Pain, Geoff. "Method for Production of Uniform Thin Films from the Vapour Phase". Australian Journal of Physics 46, nr 1 (1993): 121. http://dx.doi.org/10.1071/ph930121.
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A general method is described for production of uniform thin films from the vapour phase. A brief review of the prior art reveals that various approaches to this problem, and in particular substrate rotation, fail to achieve uniformity of thickness and composition in such technologies as molecular beam epitaxy (MBE) or chemical vapour deposition (CVD). The new technique, for which patent protection has been obtained, involves establishment of uniform growth conditions in one direction, and translation of the substrate at a constant rate in a direction perpendicular to the first. The effect is to integrate and average any property in the direction of translation, so that every point on the substrate experiences an identical history, ensuring complete uniformity of the deposited film.
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AUBERTON-HERVÉ, A. J., i MICHEL BRUEL. "WHY CAN SMART CUT® CHANGE THE FUTURE OF MICROELECTRONICS?" International Journal of High Speed Electronics and Systems 10, nr 01 (marzec 2000): 131–46. http://dx.doi.org/10.1142/s0129156400000179.
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Deposition techniques like chemical vapor deposition (CVD) offer to the semiconductor industry the initial flexibility to deposit thin films of key materials on many kinds of substrates. The homoepitaxy or hetroepitaxy techniques using CVD or molecular beam epitaxy (MBE) add the flexibility to get a pure monocrystalline thin film but with a major limitation: the starting substrate has to be monocrystalline. The missing technology has always been the one which allows the growth of a thin monocrystalline film on any kind of substrate. Hydrogen induced splitting (known today as Smart Cut®), discovered at the LETI laboratory in 1991, provides a unique opportunity to get crystalline layers on any kind of substrate. Therefore, a new tool is offered to the semiconductor industry, for new material developments and new structures. This technique is in use in production today on a first application: silicon-on-insulator (SOI) wafers which consist of a monocrystalline film of silicon on a thin amorphous silicon dioxide layer, on top of a silicon wafer. We will discuss the SOI application of the Smart Cut® technology and present other recently demonstrated breakthroughs in new material development, including SiC, compound semiconductor or 3D structures.
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Sibanda, David, Sunday Temitope Oyinbo, Tien-Chien Jen i Ayotunde Idris Ibitoye. "A Mini Review on Thin Film Superconductors". Processes 10, nr 6 (14.06.2022): 1184. http://dx.doi.org/10.3390/pr10061184.
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Thin superconducting films have been a significant part of superconductivity research for more than six decades. They have had a significant impact on the existing consensus on the microscopic and macroscopic nature of the superconducting state. Thin-film superconductors have properties that are very different and superior to bulk material. Amongst the various classification criteria, thin-film superconductors can be classified into Fe based thin-film superconductors, layered titanium compound thin-film superconductors, intercalation compounds of layered and cage-like structures, and other thin-film superconductors that do not fall into these groups. There are various techniques of manufacturing thin films, which include atomic layer deposition (ALD), chemical vapour deposition (CVD), physical vapour deposition (PVD), molecular beam epitaxy (MBE), sputtering, electron beam evaporation, laser ablation, cathodic arc, and pulsed laser deposition (PLD). Thin film technology offers a lucrative scheme of creating engineered surfaces and opens a wide exploration of prospects to modify material properties for specific applications, such as those that depend on surfaces. This review paper reports on the different types and groups of superconductors, fabrication of thin-film superconductors by MBE, PLD, and ALD, their applications, and various challenges faced by superconductor technologies. Amongst all the thin film manufacturing techniques, more focus is put on the fabrication of thin film superconductors by atomic layer deposition because of the growing popularity the process has gained in the past decade.
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Martínez, Karí, Alexey Minenkov, Johannes Aberl, Moritz Brehm i Heiko Groiss. "In situ TEM thermal study of MBE and CVD GeSn layers: Cross-section and plan-view geometries". BIO Web of Conferences 129 (2024): 24009. http://dx.doi.org/10.1051/bioconf/202412924009.
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Yang, Rongbang, Haoming Wei, Gongbin Tang, Bingqiang Cao i Kunfeng Chen. "Advanced Crystallization Methods for Thin-Film Lithium Niobate and Its Device Applications". Materials 18, nr 5 (21.02.2025): 951. https://doi.org/10.3390/ma18050951.
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Lithium niobate (LiNbO3) has remarkable ferroelectric properties, and its unique crystal structure allows it to undergo significant spontaneous polarization. Lithium niobate plays an important role in the fields of electro-optic modulation, sensing and acoustics due to its excellent electro-optic and piezoelectric properties. Thin-film LiNbO3 (TFLN) has attracted much attention due to its unique physical properties, stable properties and easy processing. This review introduces several main preparation methods for TFLN, including chemical vapor deposition (CVD), molecular beam epitaxy (MBE), pulsed laser deposition (PLD), magnetron sputtering and Smartcut technology. The development of TFLN devices, especially the recent research on sensors, memories, optical waveguides and EO modulators, is introduced. With the continuous advancement of manufacturing technology and integration technology, TFLN devices are expected to occupy a more important position in future photonic integrated circuits.
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Susanto, Iwan, Hong-Shan Liu, Yen-Ten Ho i Ing-Song Yu. "Epitaxial Growth of GaN Films on Chemical-Vapor-Deposited 2D MoS2 Layers by Plasma-Assisted Molecular Beam Epitaxy". Nanomaterials 14, nr 8 (22.04.2024): 732. http://dx.doi.org/10.3390/nano14080732.
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The van der Waals epitaxy of wafer-scale GaN on 2D MoS2 and the integration of GaN/MoS2 heterostructures were investigated in this report. GaN films have been successfully grown on 2D MoS2 layers using three different Ga fluxes via a plasma-assisted molecular beam epitaxy (PA-MBE) system. The substrate for the growth was a few-layer 2D MoS2 deposited on sapphire using chemical vapor deposition (CVD). Three different Ga fluxes were provided by the gallium source of the K-cell at temperatures of 825, 875, and 925 °C, respectively. After the growth, RHEED, HR-XRD, and TEM were conducted to study the crystal structure of GaN films. The surface morphology was obtained using FE-SEM and AFM. Chemical composition was confirmed by XPS and EDS. Raman and PL spectra were carried out to investigate the optical properties of GaN films. According to the characterizations of GaN films, the van der Waals epitaxial growth mechanism of GaN films changed from 3D to 2D with the increase in Ga flux, provided by higher temperatures of the K-cell. GaN films grown at 750 °C for 3 h with a K-cell temperature of 925 °C demonstrated the greatest crystal quality, chemical composition, and optical properties. The heterostructure of 3D GaN on 2D MoS2 was integrated successfully using the low-temperature PA-MBE technique, which could be applied to novel electronics and optoelectronics.
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Baba, Motoyoshi, Tianqing Jia, Masayuki Suzuki i Hiroto Kuroda. "Femtosecond Laser Induced Nanowire Technique and Its Applications". ISRN Nanotechnology 2011 (7.06.2011): 1–7. http://dx.doi.org/10.5402/2011/907390.
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Semiconductor nanowires are very attractive due to their interesting fundamental properties and enormous potentials for device applications to the nanoscale optoelectronics and solar cells, and so forth. We fabricated semiconductor nanowires of various wire parameters such as wire length, diameter, and density by femtosecond laser induced method. We report the development of our technology of creating semiconductor nanowires with smaller size than the laser wavelength at precise position by femtosecond laser ablation technique. There are a variety of growth methods for nanowires including chemical vapor deposition (CVD), molecular-beam epitaxy (MBE), and pulsed laser deposition (PLD). Although PLD has recently been applied as a growth method for nanowires, laser induced nanowires are very good in quality. Their growth rate is much higher than that of nanowires grown by other ways. We discuss the growth mechanism of laser induced nanowires and describe the advantages of this approach.
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Twigg, M. E., E. D. Richmond i J. G. Pellegrino. "The relaxation of compressive biaxial strains in SOS via microtwins". Proceedings, annual meeting, Electron Microscopy Society of America 47 (6.08.1989): 608–9. http://dx.doi.org/10.1017/s0424820100155013.
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For heteroepitaxial systems, such as silicon on sapphire (SOS), microtwins occur in significant numbers and are thought to contribute to strain relief in the silicon thin film. The size of this contribution can be assessed from TEM measurements, of the differential volume fraction of microtwins, dV/dν (the derivative of the microtwin volume V with respect to the film volume ν), for SOS grown by both chemical vapor deposition (CVD) and molecular beam epitaxy (MBE).In a (001) silicon thin film subjected to compressive stress along the [100] axis , this stress can be relieved by four twinning systems: a/6[211]/( lll), a/6(21l]/(l1l), a/6[21l] /( l1l), and a/6(2ll)/(1ll).3 For the a/6[211]/(1ll) system, the glide of a single a/6[2ll] twinning partial dislocation draws the two halves of the crystal, separated by the microtwin, closer together by a/3.
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Stepanova, A. N., J. Liu, K. N. Christensen, U. T. Son, K. J. Bachmann, E. I. Givargizov i J. J. Hren. "TEM study of chemically converted SiC thin film on nanometer curved Si surface". Proceedings, annual meeting, Electron Microscopy Society of America 51 (1.08.1993): 818–19. http://dx.doi.org/10.1017/s0424820100149921.
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Silicon whiskers with nanometer curvature have a variety of applications such as probes in STM and AFM, or field emission cathodes for vacuum microelectronic devices. For these and other applications it is essential to stabilize the sharply curved silicon surface during usage. Carburization of the silicon surface seems to be a very suitable solution to this problem, since SiC crystals have excellent physical properties and are chemically quite inert. There have been a number of reports of the carburization of flat surface silicon wafers by chemical reaction using both CVD and MBE methods. However, to carburize while maintaining a very sharp silicon tip is extremely difficult. It is also desirable to carburize only a very thin layer, so as to avoid excessive mechanical strain arising from the large difference (∼20%) in lattice parameters.Our carburizations were carried out in a turbo-pumped ultra-high vacuum system. The silicon specimens were oxidation sharpened and cleaned in a buffered HF solution.
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Baribeau, J. M., i H. Lafontaine. "X-Ray scattering investigation of the interfaces in Si/Si1−xGex superlattices on Si(001) grown by MBE and UHV-CVD". Thin Solid Films 321, nr 1-2 (maj 1998): 141–47. http://dx.doi.org/10.1016/s0040-6090(98)00463-5.
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Mantese, J. V., A. L. Micheli, A. H. Hamdi i R. W. Vest. "Metalorganic Deposition (MOD): A Nonvacuum, Spin-on, Liquid-Based, Thin Film Method". MRS Bulletin 14, nr 10 (październik 1989): 48–53. http://dx.doi.org/10.1557/s0883769400061492.
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There are many methods of depositing thin film materials: thermal evaporation, sputtering, electron or laser beam evaporation, chemical vapor deposition (CVD), and molecular beam epitaxy (MBE). A good survey of many of the deposition methods appears in the 1988 November and December issues of the MRS BULLETIN. One method not included in that survey, however, is metalorganic deposition (MOD), a powerful method for depositing a variety of materials.Metalorganic deposition is not to be confused with metalorganic chemical vapor deposition (MOCVD), which is a gaseous deposition method. MOD is a nonvacuum, liquid-based, spin-on method of depositing thin films. A suitable organic precursor, dissolved in solution, is dispensed onto a substrate much like photoresist. The substrate is spun at a few thousand revolutions per minute, removing the excess fluid, driving off the solvent, and uniformly coating the substrate surface with an organic film a few microns thick. The soft metalorganic film is then pyrolyzed in air, oxygen, nitrogen, or other suitable atmosphere to convert the metalorganic precursors to their constituent elements, oxides, or other compounds. Figure 1 shows a schematic of the deposition process including a prebake and annealing (if necessary).
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Abdullah, Qahtan Nofan, Fong Kwong Yam, Yushamdan Yusof i Hassan Zainuriah. "Fabrication Gallium Nitride (GaN) Nanowires by Thermal Chemical Vapor Deposition (TCVD) Technique". Advanced Materials Research 925 (kwiecień 2014): 450–54. http://dx.doi.org/10.4028/www.scientific.net/amr.925.450.
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In this paper, low-dimensional gallium nitride (GaN) nanowires have been successfully grown on silicon substrate through thermal chemical vapor deposition (TCVD); no metal catalyst was used to assist growth of nanostructure. A high purity of gallium nitride powder was used as a starting material, evaporated at 1150OC for 2 hour and then annealing at temperature 1000OC under stable flow of ammonia (NH3) gas in horizontal quartz tube. The morphological investigation and crystalline and orientations growth of GaN nanostructure were carried out by employing scanning electron microscopy (SEM), high resolution X-ray diffractmeter (HRXRD). A room temperature micro-Raman spectrum were employed to study the optical properties and crystalline defects. XRD shows the diffraction peaks located at 2θ= 32.43, 34.57, 36.89, 48.05, 57.83, 63.62, 69.02, and 70.470corresponding to the (100 ), (002), (101), (102), (110) , (103),(112 ) and (201) plane diffraction of GaN structure. These results revealed that the diffraction peaks can be attributed to hexagonal GaN phase with lattice constant of a = 3.190 A° and c = 5.1890 A°. Here we report on the growth of GaN nanowires on Si (111) substrate by CVD . This technique is much simpler and cheaper than such techniques as MBE, MOCVD and HVPE.
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Cantelli, V., O. Geaymond, O. Ulrich, T. Zhou, N. Blanc i G. Renaud. "TheIn situgrowth of Nanostructures on Surfaces (INS) endstation of the ESRF BM32 beamline: a combined UHV–CVD and MBE reactor forin situX-ray scattering investigations of growing nanoparticles and semiconductor nanowires". Journal of Synchrotron Radiation 22, nr 3 (9.04.2015): 688–700. http://dx.doi.org/10.1107/s1600577515001605.
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This paper presents the upgraded `In situ growth of Nanoscructures on Surfaces' (INS) endstation of the InterFace beamline IF-BM32 at the European Synchrotron Radiation Facility (ESRF). This instrument, originally designed to investigate the structure of clean surfaces/interfaces/thin-films by surface X-ray diffraction, has been further developed to investigate the formation and evolution of nanostructures by combining small- and wide-angle X-ray scattering methodologies,i.e.grazing-incidence small-angle X-ray scattering (GISAXS) and grazing-incidence X-ray diffraction (GIXD). It consists of a UHV chamber mounted on az-axis type goniometer, equipped with residual gas analysis, reflection high-energy electron diffraction (RHEED) and Auger electron spectroscopy (AES) to complete the X-ray scattering investigations. The chamber has been developed so as up to eight sources of molecular beam epitaxy (MBE) can be simultaneously mounted to elaborate the nanostructures. A chemical vapor deposition (CVD) set-up has been added to expand the range of growing possibilities, in particular to investigatein situthe growth of semiconductor nanowires. This setup is presented in some detail, as well as the firstin situX-ray scattering measurements during the growth of silicon nanowires.
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Toma, Fatema Tuz Zohora, Md Sharifur Rahman, Kazi Md Amjad Hussain i Syed Ahmed. "Thin Film Deposition Techniques: A Comprehensive Review". Journal of Modern Nanotechnology 4 (21.11.2024): 6. http://dx.doi.org/10.53964/jmn.2024006.
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Objective: This article presents a comprehensive review of thin film preparation techniques, focusing on their theoretical foundations, practical applications, and recent advancements in the field of materials science. Methods: The review begins with thermal evaporation, a widely used method praised for its simplicity and effectiveness in producing high - purity films. This technique relies on the principle of thermal vaporization, where materials are heated to evaporate and subsequently condense on a substrate. Next, sputtering is discussed for its versatility in depositing various materials, providing excellent film adhesion and uniformity. This technique is vital for applications in magnetic materials and photovoltaics, with an emphasis on the role of process parameters in achieving desired film characteristics. The article continues with chemical vapor deposition (CVD) and its low - pressure variant, Low - Pressure chemical vapor deposition (LPCVD). These methods are recognized for creating conformal coatings with precise thickness control, essential in integrated circuit manufacturing. The review highlights the gas - phase reactions and surface kinetics that drive these deposition processes. Plasma - enhanced chemical vapor deposition (PECVD) is examined for its advantages in depositing films at lower temperatures compared to traditional CVD. This method utilizes plasma to enhance chemical reactions, allowing for the deposition of a wide variety of materials on temperature - sensitive substrates, including dielectrics and semiconductors. Molecular beam epitaxy (MBE) is highlighted for its atomic - level precision in film deposition, critical for nanotechnology applications. The mechanisms of MBE are discussed, emphasizing its importance in producing high - quality semiconductor materials and multilayer structures. The review also covers atomic layer deposition (ALD), known for its capability to deposit films with atomic - scale control, making it essential for fabricating high - k dielectrics and quantum dots. The article elaborates on the sequential self - limiting reactions that characterize ALD processes. Additionally, chemical bath deposition (CBD) is introduced as a cost - effective method for depositing metal chalcogenides and oxides, particularly in solar cell applications. The principles of CBD are discussed, including how supersaturation in solution facilitates uniform film growth. Results: Thin films are pivotal in various technological domains, including electronics, optoelectronics, energy conversion, and sensor technologies. Given their significance, a thorough understanding of the different deposition methods is essential for developing high - performance materials and devices. Conclusion: In summary, the article addresses the future prospects of thin film deposition techniques, emphasizing the need for ongoing research to enhance film quality, optimize processes, and expand the range of applicable materials. This review serves as a valuable resource for researchers and practitioners, providing insights into the diverse methodologies available for thin film preparation and their implications for advancing technology in various fields. The synthesis of these techniques illustrates the dynamic landscape of thin film technology, underlining its critical role in future innovations.
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Nanver, Lis K., Tihomir Knezevic, Xingyu Liu, Shivakumar D. Thammaiah i Max Krakers. "On the Many Applications of Nanometer-Thin Pure Boron Layers in IC and Microelectromechanical Systems Technology". Journal of Nanoscience and Nanotechnology 21, nr 4 (1.04.2021): 2472–82. http://dx.doi.org/10.1166/jnn.2021.19112.
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An overview is given of the many applications that nm-thin pure boron (PureB) layers can have when deposited on semiconductors such as Si, Ge, and GaN. The application that has been researched in most detail is the fabrication of nm-shallow p+n-like Si diode junctions that are both electrically and chemically very robust. They are presently used commercially in photodiode detectors for extremeultraviolet (EUV) lithography and scanning-electron-microscopy (SEM) systems. By using chemicalvapor deposition (CVD) or molecular beam epitaxy (MBE) to deposit the B, PureB diodes have been fabricated at temperatures from an optimal 700 °C to as low as 50 °C, making them both front- and back-end-of-line CMOS compatible. On Ge, near-ideal p+n-like diodes were fabricated by covering a wetting layer of Ga with a PureB capping layer (PureGaB). For GaN high electron mobility transistors (HEMTs), an Al-on-PureB gate stack was developed that promises to be a robust alternative to the conventional Ni-Au gates. In MEMS processing, PureB is a resilient nm-thin masking layer for Si micromachining with tetramethyl ammonium hydroxide (TMAH) or potassium hydroxide (KOH), and low-stress PureB membranes have also been demonstrated.
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Kawasaki, Masashi, i Masashi Nantoh. "Crystal Growth and Atomic-Level Characterization of YBa2Cu3O7–δ Epitaxial Films". MRS Bulletin 19, nr 9 (wrzesień 1994): 33–38. http://dx.doi.org/10.1557/s0883769400047965.
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Epitaxial thin-film growth of high-critical-temperature (Tc) superconductors has been intensively studied not only because it is one of the key technologies for electronic application but also because it provides suitable specimens for elucidating the superconducting mechanism. For simply making thick (>100 nm) epitaxial films, various deposition techniques such as sputtering, pulsed laser deposition (PLD), evaporation, including molecular beam epitaxy (MBE), and chemical vapor deposition (CVD) have been verified as applicable. For instance, high-quality YBa2Cu3O7–δ (YBCO) films, in terms of superconducting properties (Tc and critical current Jc), can be made by adjusting the cationic composition and choosing the right deposition conditions, e.g., oxygen pressure and temperature close to the decomposition line in the phase diagram. The knowledge and techniques accumulated in the high Tc field have been successfully transferred for the film growth of such oxides as dielectric, ferroelectric, magnetic, and optically functional materials. Pulsed laser deposition, especially, is now widely used for those materials and was addressed in a previous issue of the MRS Bulletin. However, as the demand for film quality increases, allowing films to be used in complex heterostructures like Josephson tunnel junctions and in well-designed physics studies, the meaning of the term “highquality film” has been changing.
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Sultanov, Numonjon A., Zokirjon X. Mirzajonov, Fakhriddin T. Yusupov i Tokhirbek I. Rakhmonov. "Nanocrystalline ZnO Films on Various Substrates: A Study on Their Structural, Optical, and Electrical Characteristics". East European Journal of Physics, nr 2 (1.06.2024): 309–14. http://dx.doi.org/10.26565/2312-4334-2024-2-35.
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Zinc oxide (ZnO), characterized by its wide bandgap and substantial exciton binding energy, is extensively utilized in optoelectronic applications, including blue and ultraviolet light-emitting diodes (LEDs) and lasers. In this study, the deposition of ZnO films on various substrates (Si, sapphire, GaAs, GaP) through thermal oxidation is investigated as a cost-effective alternative to molecular beam epitaxy (MBE) and chemical vapor deposition (CVD). A thorough analysis of the structural, optical, and electrical properties of these films is presented, with a focus on their suitability for heterojunction diodes. The methodology employed involved the thermal evaporation of Zn films in a vacuum chamber, followed by oxidation in a pure oxygen atmosphere. The conditions for deposition were optimized to yield nanocrystalline ZnO films with a preferential orientation, as confirmed by X-ray diffraction (XRD) analysis. An increase in the optical bandgap was indicated by optical transmittance measurements, while photoluminescence (PL) spectra exhibited uniform and enhanced crystalline integrity across the samples. The electrical characterization of ZnO-based heterojunction diodes on different substrates revealed distinct electrical characteristics, with variations in leakage current and ideality factor observed. The specific resistances of the Zinc Oxide (ZnO) films were determined by analyzing the linear portions of the current-voltage (I-V) curves.
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Rahaman, Imteaz, Hunter D. Ellis, Cheng Chang, Dinusha Herath Mudiyanselage, Mingfei Xu, Bingcheng Da, Houqiang Fu, Yuji Zhao i Kai Fu. "Epitaxial Growth of Ga2O3: A Review". Materials 17, nr 17 (28.08.2024): 4261. http://dx.doi.org/10.3390/ma17174261.
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Beta-phase gallium oxide (β-Ga2O3) is a cutting-edge ultrawide bandgap (UWBG) semiconductor, featuring a bandgap energy of around 4.8 eV and a highly critical electric field strength of about 8 MV/cm. These properties make it highly suitable for next-generation power electronics and deep ultraviolet optoelectronics. Key advantages of β-Ga2O3 include the availability of large-size single-crystal bulk native substrates produced from melt and the precise control of n-type doping during both bulk growth and thin-film epitaxy. A comprehensive understanding of the fundamental growth processes, control parameters, and underlying mechanisms is essential to enable scalable manufacturing of high-performance epitaxial structures. This review highlights recent advancements in the epitaxial growth of β-Ga2O3 through various techniques, including Molecular Beam Epitaxy (MBE), Metal-Organic Chemical Vapor Deposition (MOCVD), Hydride Vapor Phase Epitaxy (HVPE), Mist Chemical Vapor Deposition (Mist CVD), Pulsed Laser Deposition (PLD), and Low-Pressure Chemical Vapor Deposition (LPCVD). This review concentrates on the progress of Ga2O3 growth in achieving high growth rates, low defect densities, excellent crystalline quality, and high carrier mobilities through different approaches. It aims to advance the development of device-grade epitaxial Ga2O3 thin films and serves as a crucial resource for researchers and engineers focused on UWBG semiconductors and the future of power electronics.
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Concepción Díaz, Omar, Nicolaj Brink Søgaard, Oliver Krause, Jin Hee Bae, Thorsten Brazda, Andreas T. Tiedemann, Qing-Tai Zhao, Detlev Grützmacher i Dan Buca. "(Si)GeSn Isothermal Multilayer Growth for Specific Applications Using GeH4 and Ge2H6". ECS Meeting Abstracts MA2022-02, nr 32 (9.10.2022): 1162. http://dx.doi.org/10.1149/ma2022-02321162mtgabs.
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The experimental demonstration of Ge1-xSnx alloys lasers opened group-IV materials towards high-performance electronic and photonic devices that can be easily integrated with the current Si semiconductor technology. In recent years, GeSn-based optoelectronic devices including light-emitting and detectors, modulators, and CMOS have been proven. The major challenges for the Ge1-xSnx epitaxy arise from the low solid solubility of Sn in Ge, the large lattice mismatch, and the reduced thermal stability between Ge and Sn. All these are becoming extremely critical at higher Sn contents. Non-equilibrium conditions offered by molecular beam epitaxy (MBE), chemical vapor deposition (CVD), flash lamp, or laser annealing have been lately investigated. Between them, CVD is to date the preferred growth technique for its current development compatible with the industry offering micron-thick layers with the highest crystal quality. While Tin-tetrachloride (SnCl4) becomes the standard Sn precursor, for Ge different gasses, like germane (GeH4) and digermane (Ge2H6) are used attempting to archive high Sn incorporation and high material quality. While Ge1-xSnx films with the same high Sn content can be obtained regardless of the used precursor, the advantages and disadvantages of each precursor are discussed in this work. The use of Ge2H6 is accompanied by high growth rates, being favorable in applications where relatively thick films are needed, such as laser structures. On the other hand, with a relatively low growth rate, GeH4 provides a greater thickness control, achieving clear and sharp interfaces in heterostructures. For this reason, GeH4 is the appropriate precursor for quantum transport or spintronic. The biggest challenge in heterostructure designs is going up and down in Sn content. The growth of a Ge1-ySny on a Ge1-xSnx, y<x, or SiGeSn layer cannot be performed by increasing the growth temperature. Post-annealing processes lead to strong crystallinity degradation of the already grown layer by strong Sn diffusion or Sn segregation due to the limited thermal stability of Ge1-xSnx alloys. In this work, we address simple methodologies to enhance the gradient or step Sn content without changing the process temperature. Controlling only the carrier gas flow while keeping the standard growth parameters constant, high-quality Ge1-xSnx alloys with uniform Sn content up to 15 at.% are obtained. The proposed method acts as guidance to produce Ge1-xSnx heterostructures that can be extended to any CVD reactor, independently of the used precursor, GeH4 or Ge2H6. Different devices structures are presented proving the applicability of the isothermal multilayer growth. Figure 1
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Tao, Meng. "Valence-Mending Passivation of Si(100) Surface: Principle, Practice and Application". Solid State Phenomena 242 (październik 2015): 51–60. http://dx.doi.org/10.4028/www.scientific.net/ssp.242.51.
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Surface states have hindered and degraded many semiconductor devices since the Bardeen era. Surface states originate from dangling bonds on the surface. This paper discusses a generic solution to surface states, i.e. valence-mending passivation. For the Si (100) surface, a single atomic layer of valence-mending sulfur, selenium or tellurium can terminate ~99% of the dangling bonds, while group VII fluorine or chlorine can terminate the remaining 1%. Valence-mending passivation of Si (100) has been demonstrated using CVD, MBE and solution passivation. The keys to valence-mending passivation include an atomically-clean Si (100) surface for passivation and precisely one monolayer of valence-mending atoms on the surface. The passivated surface exhibits unprecedented properties. Electronically the Schottky barrier height between various metals and valence-mended Si (100) now follows more closely the Mott-Schottky theory. With metals of extreme workfunctions, new records for low and high Schottky barriers are created on Si (100). The highest barrier so far is 1.14 eV, i.e. a larger-than-bandgap barrier, and the lowest barrier is below 0.08 eV and potentially negative. Chemically silicidation between metal and valence-mended Si (100) is suppressed up to 500 °C, and the thermally-stable record Schottky barriers enable their applications in nanoelectronic, optoelectronic and photovoltaic devices. Another application is transition metal dichalcogenides. Valence-mended Si (100) is an ideal starting surface for growth of dichalcogenides, as it provides only van der Waals bonding to the dichalcogenide.
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Schwarz, Daniel, Sören Christopher Schäfer, Christian Spieth i Michael Oehme. "(Invited) Advanced Virtual Sigesn Substrates for the Monolithic Integration of Novel Opto- and Nanoelectronics ". ECS Meeting Abstracts MA2024-02, nr 32 (22.11.2024): 2343. https://doi.org/10.1149/ma2024-02322343mtgabs.
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In the past three decades, the ternary alloy semiconductor SiGeSn has evolved from a predicted direct semiconductor to a serious candidate for the realization of a myriad of interesting applications. The fields of application vary from novel transistor concepts 1–4 for up-coming processor generations to the already reported electrically pumped heterostructure laser diode 5–7, the last missing key component for the monolithically integrated optical on-chip communication on Si. This rise of SiGeSn originates mainly due to its ability of decoupling its bandgap from its lattice-constant by what it is predestined for the epitaxy of strain-reduced heterostructures and thus their monolithic integration on Si using the well-established Ge virtual substrate technology 8. However, utilizing the lattice-matching on Ge limits the epitaxy of strain-reduced heterostructures to an extremely narrow composition range of SiGeSn, for which a constant concentration ratio of Si to Sn of 3.67 needs to be fulfilled. In addition, the composition ranges of the more desirable direct bandgap SiGeSn require lattice-constants which are much larger than that of Ge, and thus a GeSn virtual substrate. Therefore, unlocking an even larger composition range necessitates a reliable technology for complete strain-relaxation of GeSn. However, up to this day, the complete strain-relaxation of GeSn proves itself quite challenging due to its limited thermal budget. In the case of chemical vapour deposition (CVD) based epitaxy, only partial relaxation occurs during growth, while the complete strain-relaxation is limited to post-growth methods like clearance etching for the strain relief of the resulting free-standing structures. Besides that, during the low-temperature molecular beam epitaxy (MBE) of GeSn, there is insufficient thermal energy for the formation of misfit dislocations. Therefore, MBE grown GeSn structures are typically pseudomorphic or show a very small degree of strain-relaxation. Nevertheless, various approaches, like post-growth annealing (PGA) have been investigated and reported to achieve partial relaxation up to 89 % 9. On top of that, partially relaxed GeSn buffers typically exhibit a surface roughness in the range of a few nanometres which is disadvantageous for high-performance heterostructures with individual layer thicknesses of a few tens of nanometres. A possible approach to counteract this problem is the introduction of surface smoothening steps such as using chemical mechanical polishing (CMP). In this work, we report the development of a combined fabrication scheme of MBE, PGA and CMP to achieve a GeSn double layer buffer stack with a final Sn concentration of 10 %, almost complete strain-relaxation and a surface roughness of ≈ 1.7 nm. A schematic overview of the process and the involved corresponding layer stacks is shown in Fig. 1a. All shown epitaxy experiments were performed in a 6” MBE system, where Si, Ge and Sn are used as matrix materials and B and Sb as dopants, respectively. In order to stabilize the Sn segregation in the low-temperature growth regime of SiGeSn at TS ≤ 200 °C, the substrate temperature is precisely measured and controlled in-situ using mid-infrared pyrometry 10. The development of the GeSn virtual substrates is based on the well-reported Ge virtual substrate on Si(001) 8, followed by an additional 100 nm thick Ge buffer layer. For the actual GeSn virtual substrate, a 400 nm thick GeSn layer with 6% Sn underwent PGA in a rapid thermal annealing system, subsequent to its growth. To achieve a best possible growth interface, a CMP step was used afterwards to smoothen the surface. Atomic force microscopy images of a final strain-relaxed GeSn virtual substrate with and without CMP are compared in Fig. 1b, where a nice cross-hatch pattern can be seen for the sample with CMP. The crucial step is then the growth continuation, which necessitates the effective removal of the native GeSn oxide. For this, a combination of wet etching via hydrogen chloride and a following in-situ soft thermal desorption at TS = 300 °C has proven itself as best solution 11. A final 400 nm thick GeSn layer with 10 % Sn completes the GeSn virtual substrate. This virtual substrate forms then the basis for the subsequent device growth, with the layer stack shown in Fig. 1c, and their fabrication using standard cleanroom processes, as described in an earlier report 11. The current voltage characteristics of an exemplary device with a diameter of 4 µm in Fig. 1d proves a good device functionality. Alongside to the latest results on the current development of GeSn virtual substrates using MBE, we provide an overview of past and future approaches for the realization of virtual SiGeSn substrates and their suitability for monolithically integrated SiGeSn heterostructures on Si. Figure 1
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Auciello, O., A. I. Kingon i S. B. Krupanidhi. "Sputter Synthesis of Ferroelectric Films and Heterostructures". MRS Bulletin 21, nr 6 (czerwiec 1996): 25–30. http://dx.doi.org/10.1557/s0883769400046042.
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Ferroelectric films can display a wide range of dielectric, ferroelectric, piezoelectric, electrostrictive, and pyroelectric properties. The potential utilization of these properties in a new generation of devices has driven the intensive studies on the synthesis, characterization, and determination of processing-microstructure-property relationships of ferroelectric thin films during the last five years. In addition there has been an increased drive for integrating ferroelectric film-based heterostructures with different substrate materials to demonstrate numerous devices that exploit the dielectric, ferroelectric, piezoelectric, electrostrictive, and pyroelectric properties of these materials. For example the high dielectric permittivities of perovskite-type materials can be advantageously used in dynamic random-access memories (DRAMs), while the large values of switchable remanent polarization of ferroelectric materials are suitable for nonvolatile ferroelectric random-access memories (NVFRAMs).Various vapor-phase deposition techniques such as plasma and ion-beam sputter deposition (PSD and IBSD, respectively), pulsed laser-ablation deposition (PLAD), electron-beam or oven-induced evaporation for molecular-beam epitaxy (MBE), and chemical vapor deposition (CVD) have been applied to produce ferroelectric films and layered heterostructures. See References 4–7 for recent reviews. However, work is still necessary to optimize the techniques to produce device-quality films on large semiconductor substrates in a way that is fully compatible with existing semiconductor process technology. Therefore research efforts should be focused on the optimization of suitable process methods and on the investigation of processing-composition-microstructure property relationships. These efforts are the focus of this article with emphasis on PSD and IBSD techniques.
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Moumen, Abderrahim, Gayan C. W. Kumarage i Elisabetta Comini. "P-Type Metal Oxide Semiconductor Thin Films: Synthesis and Chemical Sensor Applications". Sensors 22, nr 4 (10.02.2022): 1359. http://dx.doi.org/10.3390/s22041359.
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This review focuses on the synthesis of p-type metal-oxide (p-type MOX) semiconductor thin films, such as CuO, NiO, Co3O4, and Cr2O3, used for chemical-sensing applications. P-type MOX thin films exhibit several advantages over n-type MOX, including a higher catalytic effect, low humidity dependence, and improved recovery speed. However, the sensing performance of CuO, NiO, Co3O4, and Cr2O3 thin films is strongly related to the intrinsic physicochemical properties of the material and the thickness of these MOX thin films. The latter is heavily dependent on synthesis techniques. Many techniques used for growing p-MOX thin films are reviewed herein. Physical vapor-deposition techniques (PVD), such as magnetron sputtering, thermal evaporation, thermal oxidation, and molecular-beam epitaxial (MBE) growth were investigated, along with chemical vapor deposition (CVD). Liquid-phase routes, including sol–gel-assisted dip-and-spin coating, spray pyrolysis, and electrodeposition, are also discussed. A review of each technique, as well as factors that affect the physicochemical properties of p-type MOX thin films, such as morphology, crystallinity, defects, and grain size, is presented. The sensing mechanism describing the surface reaction of gases with MOX is also discussed. The sensing characteristics of CuO, NiO, Co3O4, and Cr2O3 thin films, including their response, sensor kinetics, stability, selectivity, and repeatability are reviewed. Different chemical compounds, including reducing gases (such as volatile organic compounds (VOCs), H2, and NH3) and oxidizing gases, such as CO2, NO2, and O3, were analyzed. Bulk doping, surface decoration, and heterostructures are some of the strategies for improving the sensing capabilities of the suggested pristine p-type MOX thin films. Future trends to overcome the challenges of p-type MOX thin-film chemical sensors are also presented.
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Wan, Hsien-Wen, Yi-Ting Cheng, Chao-Kai Cheng, Tun-Wen Pi, Jueinai Kwo i Minghwei Hong. "(Invited) Thin Epitaxial Single-Crystal Si on Sige Followed By in-Situ Deposition of High-k Dielectrics – Novel Gate Stacks for Achieving Extremely Low Dit and Highly Reliable SiGe MOS". ECS Meeting Abstracts MA2022-01, nr 19 (7.07.2022): 1067. http://dx.doi.org/10.1149/ma2022-01191067mtgabs.
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Silicon-germanium (SiGe) is replacing silicon (Si) as the channel layer for the p-type metal-oxide-semiconductor (pMOS) in the aggressively scaled complementary MOS (CMOS) technology. Many research efforts involving SiGe gate stacks have resulted in the attainment of low interfacial trap densities (Dits). Si-passivated SiGe gate stacks are the most promising method to achieve both low Dit and high device reliability. However, regardless of the growth methods, most publications reported the pileup of Ge atoms on top of the grown Si even after extensive treatments. The subsequent process in forming gate stacks, including oxidation, inevitably caused the segregated Ge to form GeOx, leading to degradation of the interfacial quality of the gate stacks. We have used molecular beam epitaxy (MBE) to grow thin single-crystal Si of 0.79nm thickness (six MLs) epitaxially on epi-Si1-xGex(001) under ultra-high vacuum (UHV). Different from its counterpart of chemical vapor deposition (CVD), MBE enables epi-Si growth on Ge at growth temperatures below 300 °C. The measurements using reflection high-energy electron diffraction (RHEED), high-resolution synchrotron radiation X-ray diffraction (HR-XRD), and the scanning transmission electron microscopy with high-angle annular-dark-field (STEM-HAADF) have revealed high crystallinity of the epi-Si, the Si1-xGex layers and abrupt interfaces of the high-k/epi-Si/Si1-xGex layers. Moreover, our unique capability of epi growth/analysis enabled the study of the electronic surface structures of epi-Si/epi-Ge using in-situ high-resolution synchrotron radiation photoemission spectroscopy (SRPES) via a portable sample transfer station under UHV. We have used SRPES to demonstrate that the as-grown Si1−xGex(001)-2×1 surfaces with Ge content ranging from 0.1 to 0.9 are all terminated with buckled Ge–Ge dimers, and the surface electronic structure is similar to that of epi-Ge(001)-2×1. The direct deposition of epi-Si on as-grown SiGe removed the top buckled Ge-Ge dimers, which diffused into the epi-Si and some segregated to the top of the Si. As a result, the topmost layer beneath the epi-Si was 1 ML of Ge, and the interfaces of high-k/epi-Si/Si1−xGex are similar to those of the high-k/epi-Si/Ge. Again, the hetero-interfaces of our gate dielectrics are different from those grown using CVD. The well-controlled interfaces have enabled the achievement of low interfacial trap densities (Dit) of (3 - 6) × 1011 eV-1cm-2 in these high-k/epi-Si/Si1-xGex samples. The minimum Dit values remained at 3 × 1011 eV-1cm-2 regardless of the Ge content, demonstrating the effective passivation of the low-temperature deposited epi-Si. The limited Ge segregation during the low-temperature growth of epi-Si may attribute to the attainment of the low Dit values. We have benchmarked the minimum Dit (Dit, min) of our work with other state-of-the-art SiGe gate stacks. The Dit,min values from the other efforts increased with increasing Ge content, which may be caused by the GeOx formation that was difficult to control in the high-Ge-content (HGC) Si1-xGex. The effective charge sheet densities for the Si1-xGex gate stacks were extracted via examination of capacitance-voltage (C-V) hysteresis with decreasing stress voltage in the accumulation region of the MOS capacitors. We have attained very high acceleration factors of 8-12, indicating high reliability of the HfO2/epi-Si/Si1-xGex pMOS gate stacks. Furthermore, we have used a scavenging method, consisting of a cyclic process of an O2 exposure followed by a UHV annealing, to eliminate the segregated and diffused Ge in epi-Si before high-k deposition. Upon O2 exposure at room temperature, both the Si and Ge surface atoms are simultaneously oxidized to give rise to four Si charge states and Ge suboxides, respectively. The subsequent in-situ annealing at 500 °C under UHV moved the oxygen atom in the Ge suboxides to bond with the nearby Si atom. The annealing also caused the diffused Ge inside the epi-Si to segregate to the surface. The processes of O2 exposure followed by annealing were repeated three times resulting in an oxidized Si/Ge surface having only the four Si oxidized states without GeOx, but with a minimal amount of segregated Ge.
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Qiu, Zhaobin, Ying Qiao, Wanyuan Shi i Xiaoqian Liu. "A robust framework for enhancing cardiovascular disease risk prediction using an optimized category boosting model". Mathematical Biosciences and Engineering 21, nr 2 (2024): 2943–69. http://dx.doi.org/10.3934/mbe.2024131.
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<abstract> <p>Cardiovascular disease (CVD) is a leading cause of mortality worldwide, and it is of utmost importance to accurately assess the risk of cardiovascular disease for prevention and intervention purposes. In recent years, machine learning has shown significant advancements in the field of cardiovascular disease risk prediction. In this context, we propose a novel framework known as CVD-OCSCatBoost, designed for the precise prediction of cardiovascular disease risk and the assessment of various risk factors. The framework utilizes Lasso regression for feature selection and incorporates an optimized category-boosting tree (CatBoost) model. Furthermore, we propose the opposition-based learning cuckoo search (OCS) algorithm. By integrating OCS with the CatBoost model, our objective is to develop OCSCatBoost, an enhanced classifier offering improved accuracy and efficiency in predicting CVD. Extensive comparisons with popular algorithms like the particle swarm optimization (PSO) algorithm, the seagull optimization algorithm (SOA), the cuckoo search algorithm (CS), K-nearest-neighbor classification, decision tree, logistic regression, grid-search support vector machine (SVM), grid-search XGBoost, default CatBoost, and grid-search CatBoost validate the efficacy of the OCSCatBoost algorithm. The experimental results demonstrate that the OCSCatBoost model achieves superior performance compared to other models, with overall accuracy, recall, and AUC values of 73.67%, 72.17%, and 0.8024, respectively. These outcomes highlight the potential of CVD-OCSCatBoost for improving cardiovascular disease risk prediction.</p> </abstract>
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Vincent, Laetitia, Marcel A. Verheijen, Wouter Peeters, Hassan Melhem, Theo Van den Berg, Hafssa Ameziane, Gilles Patriarche i in. "Epitaxy of Hexagonal Ge-2H : Lessons from in Situ TEM Observations". ECS Meeting Abstracts MA2024-02, nr 32 (22.11.2024): 2340. https://doi.org/10.1149/ma2024-02322340mtgabs.
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Silicon and Germanium crystallize in the cubic diamond structure 3C with which they dominate definitely the electronics. Playing on crystal phases in semiconductors occurs to be a valuable mean of electronic band engineering. Remarkably, the hexagonal 2H phase of SiGe turns to get a direct band gap with light emission capabilities within a specific composition range (Si<35%). This material holds the promise to fill the gap between electronics and photonics industry using group IV semiconductors. We use GaAs NWs with the wurtzite structure as a template to create both (1) core/shell and (2) trunk/nanobranches heterostructures [2,3]. The GaAs-wurtzite is an ideal template to copy the structure by epitaxy forcing the Ge to adopt the hexagonal crystal phase and in turn it is used here as a textbook case The growths are followed using the in situ TEM NANOMAX. This unique microscope can be implemented either with molecular beam epitaxy (MBE) sources or with a gas injector for chemical vapor deposition (CVD). Real time TEM observations at the atomic scale show the fundamental aspects of the epitaxy and the formation of growth-related staking faults in Ge-2H. 1) On core/shell configuration[1], depending on growth conditions, different growth regimes highly impact the crystal quality of the of Ge-2H shell. On {1-100} prismatic surfaces, a regular step flow supports a flat surface and a perfect replication of the hexagonal structure However, when the step flow is destabilized, original intrinsic I3 basal stacking faults (BSF) are formed during growth. We evidence their correlation with the growth modes related to surface diffusion. Understanding the nucleation of these defects is necessary to prevent their formation during epitaxy. Possible scenarios of I3 BSF formation are discussed. Theses defects show a faulted stacking ABACABAB with only one faulted basal plane bounded by a pair of partial dislocations along <11-20> with opposite Burger vectors b=+/-1/3<1-100>. Thermal annealing induces a motion of the dislocation and an expansion of the I3 BSF resulting in a 4H stacking in the core/shell structure. 2) On wurtzite GaAs nanowires, Au catalysts are deposited on the sidewalls. Nanobranches grow with an axial direction along <1-100> and exhibit a hexagonal crystal structure[2] . With in situ observations, we study the VLS and VSS growths of Au catalyzed Ge-2H branches depending on the growth temperature. [1] L. Vincent et al. Adv. Mat. Inter. 9-16 (2022) 2102340, doi.org/10.1002/admi.202102340 [2] A Li et al. Nanotechnology 34 (2023) 015601 doi: 10.1088/1361-6528/ac9317 Figure 1
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Sousa Neto, Vicente de Oliveira, Gilberto Dantas Saraiva, A. J. Ramiro De Castro, Paulo de Tarso Cavalcante Freire i Ronaldo Ferreira Do Nascimento. "Electrodeposition of One-Dimensional Nanostructures: Environmentally Friendly Method". Journal of Composites and Biodegradable Polymers 10 (28.12.2022): 19–42. http://dx.doi.org/10.12974/2311-8717.2022.10.03.
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During the past decade, nanotechnology has become an active field of research because of its huge potential for a variety of applications. When the size of many established, well-studied materials is reduced to the nanoscale, radically improved or new surprising properties often emerge. There are mainly four types of nanostructures: zero, one, two and three dimensional structures. Among them, one-dimensional (1D) nanostructures have been the focus of quite extensive studies worldwide, partially because of their unique physical and chemical properties. Compared to the other three dimensional structures, the first characteristic of 1D nanostructure is its smaller dimension structure and high aspect ratio, which could efficiently transport electrical carriers along one controllable direction; as a consequence they are highly suitable for moving charges in integrated nanoscale systems. The second characteristic of 1D nanostructure is its device function, which can be exploited as device elements in many kinds of nanodevices. Indeed it is important to note that superior physical properties including superconductivity, enhanced magnetic coercivity and the unusual magnetic state of some 1D nanostructures have been theoretically predicted and some of them have already been confirmed by experiments. In order to attain the potential offered by 1D nanostructures, one of the most important issues is how to synthesize 1D nanostructures in large quantities with a convenient method. Many synthetic strategies, such as solution or vapor-phase approaches, template-directed methods, electrospinning techniques, solvothermal syntheses, self-assembly methods, etc., have been developed to fabricate different classes of 1D nanostructured materials, including metals, semiconductors, functional oxides, structural ceramics, polymers and composites. All the methods can be divided into two categories: those carried out in a gas phase (i.e., “dry processes”) and those carried out in a liquid phase (i.e., “wet processes”). The dry processes include, for example, techniques such as chemical vapor deposition (CVD), physical vapor deposition (PVD), pulse laser deposition (PLD), metal-organic chemical vapor deposition (MOCVD), and molecular beam epitaxy (MBE). In general, these gas phase processes require expensive and specialized equipments. The wet processes include sol-gel method, hydrothermal method, chemical bath deposition (CBD) and electrodeposition. Among the above mentioned methods, electrodeposition has many advantages such as low cost, environmentally friendly, high growth rate at relatively low temperatures and easier control of shape and size. Generally, there are two strategies to produce the 1D nanostructures through the electrochemical process. They are the template-assisted electrodeposition, and the template-free electrodeposition. In this chapter, we will approach the recent progress and offer some prospects of future directions in electrodeposition of 1D nanostructures. Electrodeposition is a simple and flexible method for the synthesis of one-dimensional (1D) nanostructures and has attracted great attention in recent years.
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Fernandez, Erwin, Dennis Friedrich, Roel van De Krol i Fatwa Abdi. "Alternate-Target Layer-By-Layer Pulsed Laser Deposition of Epitaxial BiVO4 Thin Films". ECS Meeting Abstracts MA2022-01, nr 36 (7.07.2022): 1559. http://dx.doi.org/10.1149/ma2022-01361559mtgabs.
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Bismuth vanadate (BiVO4) has emerged as one of the highest performing metal oxide photoelectrodes for solar energy-to-fuels applications [1, 2]. This achievement has been largely attributed to the development of high-quality synthesis techniques. Specifically, epitaxial synthetic routes to producing lattice-matched, near single-crystalline quality BiVO4 with minimal extrinsic defects have been essential to understand the fundamental and PEC properties of BiVO4 that are inaccessible by conventional bulk synthesis techniques. In addition, epitaxial synthesis may also be employed as a strategy to further improve the PEC properties of BiVO4 through, for instance, altering the band structure and enhancing the carrier dynamics by strain engineering. Hence, the ability to produce high-quality single-phase epitaxial BiVO4 films is desirable. To date, molecular beam epitaxy (MBE), chemical vapor deposition (CVD), and pulsed laser deposition (PLD) [3] have been used to fabricate epitaxial BiVO4 thin films, with PLD having the advantage of relatively simple experimental setup and material versatility. However, an oft-noted drawback in conventional PLD using single oxide targets is off-stoichiometry in the deposited films; this is especially so for BiVO4 which requires a Bi-rich compound target to achieve a stoichiometric BiVO4 film [4]. This problem is also expected in general for multinary oxides composed of elements with very different ablation properties. To alleviate the limitations of conventional PLD, we employ for the first time alternate-target layer-by-layer PLD as a more elegant approach to produce high quality epitaxial BiVO4 films. Briefly, constituent oxide targets are alternately ablated by an excimer laser (λ= 248 nm) to build the desired film one unit cell thick at a time. Stoichiometry is controlled by the number of shots corresponding to a specified laser fluence for the constituent oxide target. To demonstrate the method, we deposited epitaxial BiVO4 films onto (001)-oriented yttrium-stabilized zirconia (YSZ) using 4N-pure Bi2O3 and V2O5 targets. Films grown are single phase BiVO4 as shown by x-ray diffraction. Out-of-plane diffraction peaks indexed to BiVO4(00l) suggests epitaxy of the film onto the substrate; reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks further confirm the BiVO4(001) || YSZ(001) epitaxial relationship (top figure). Rocking curves of the BiVO4 (004) peak (FWHM ~ 0.015-0.041) indicate high crystalline perfection of the BiVO4 film, almost approaching that of the YSZ substrate (FWHM ~ 0.010). Thickness dependent-rocking curve studies reveal that BiVO4 films are strained to the substrate for film thicknesses under 22 nm; above this critical thickness, film relaxation ensues. In turn, the resulting optoelectronic properties of the BiVO4 film is dictated by its relaxation state. The optical band gap narrows with film relaxation as observed with spectroscopic ellipsometry. Moreover, steady-state photoluminescence emission spectroscopy reveals a sub-bandgap state (A 2, bottom figure) associated with strained BiVO4 films, on top of a state consistent with band-to-band recombination (B1 ). A higher energy sub-bandgap state (A 1, bottom figure) develops as the film relaxes. The implications of the relaxation state on the charge carrier dynamics and photoelectrochemical properties of BiVO4 will be discussed. Figure: (top) reciprocal space maps of the asymmetric BiVO4(208) and YSZ(204) peaks; (bottom) photoluminescence emission spectra of strained and relaxed BiVO4 films. References: [1] Pihosh, Y., Turkevych, I., Mawatari, K. et al. Photocatalytic generation of hydrogen by core-shell WO3/BiVO4 nanorods with ultimate water splitting efficiency. Sci Rep 5, 11141 (2015) [2] Kim, J., Jang, JW., Jo, Y. et al. Hetero-type dual photoanodes for unbiased solar water splitting with extended light harvesting. Nat Commun 7, 13380 (2016) [3] Zhang, Y., Li, G. Recent Advances of Epitaxial BiVO4 Thin Film: Preparation and Physical and Photoelectrochemical Properties. Braz J Phys 50,185 (2020). [4] Rettie, A. J. E., Mozaffari, S., McDaniel, M. D., Pearson, K. N., Ekerdt, J. G., Markert, J. T., & Mullins, C. B. Pulsed Laser Deposition of Epitaxial and Polycrystalline Bismuth Vanadate Thin Films. J Phys Chem C 118(46), 26543 (2014) Figure 1
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Liu, Yujia, Kevin-P. Gradwohl, Chen-Hsun Lu, Yuji Yamamoto, Thilo Remmele, Cedric Corley-Wiciak, Thomas Teubner, Carsten Richter, Martin Albrecht i Torsten Boeck. "Growth of 28Si Quantum Well Layers for Qubits by a Hybrid MBE/CVD Technique". ECS Journal of Solid State Science and Technology, 30.01.2023. http://dx.doi.org/10.1149/2162-8777/acb734.
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Abstract Isotopically enriched 28Si quantum well layers in SiGe/Si/SiGe heterostructures are an excellent material platform for electron spin qubits. Here, we report the fabrication of 28SiGe/28Si/28SiGe heterostructures for qubits by a hybrid molecular beam epitaxy (MBE) / chemical vapour deposition (CVD) growth, where the thick relaxed SiGe substrates are realised by a reduced-pressure CVD and the 28SiGe/28Si/28SiGe stacks are grown by MBE. We achieve a fully strained 28Si quantum well layer in such heterostructures with a 29Si concentration as low as 200 ppm within the MBE grown layers and conclude that 29Si primarily originates from the residual natural Si vapour in the MBE chamber. A reliable surface preparation combining ex-situ wet chemical cleaning and in-situ annealing and atomic hydrogen irradiation offers epitaxy ready CVD grown SiGe substrates with low carbon and oxygen impurities. Furthermore, we also present our studies about the growth temperature effect on the misfit dislocation formation in this heterostructure. This shows that the misfit dislocation formation is significantly suppressed at a low MBE growth temperature, such as 350°C.
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Twigg, M. E., J. G. Pellegrino i E. D. Richmond. "The Structure of Silicon Thin Films Grown on Sapphire by MBE". MRS Proceedings 107 (1987). http://dx.doi.org/10.1557/proc-107-389.
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AbstractFrom a series of imaging experiments performed in the transmission electron microscope (TEM), it is apparent that for silicon grown on sapphire (SOS) by molecular beam epitaxy (MBE), silicon thin film growth on the (1012) sapphire plane resembles that observed for analogous films grown by chemical vapor deposition (CVD). At 900°C very thin (150A) silicon films grow as islands with either the (001) or (110) planes parallel to the (1012) plane; it is also found that most of the silicon grows as (001) rather than (110) islands, as is true for CVD-grown SOS. The orientation, however, of (110) islands occuring in this MBE-grown SOS sample differs from that of (110) islands occuring in CVD-grown SOS. By following this initial 150A of growth with 2500A of silicon deposited at. 750°C, a continuous (001) film was grown in which microtwins appear to be the predominant defect. The MBE-grown SOS also resembles that grown by CVD in that the microtwin densities associated with the “majority” and “minority” twinning systems are influenced by the orientation of the sapphire substrate.
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Hucknall, P. K., S. Sugden, C. J. Sofield, T. C. Q. Noakes i C. F. Mcconville. "Structural and Compositional Study of Sil-xGex Multilayer Structures Using Medium Energy Ion Scattering". MRS Proceedings 379 (1995). http://dx.doi.org/10.1557/proc-379-229.
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ABSTRACTThe ability to determine structural and compositional information from the sub-surface region of a semiconductor material has been demonstrated using a new time-of-flight medium energy ion scattering spectroscopy (ToF-MEISS) system. A series of silicon-silicon/germanium (Si/Sil-xGex) hetero-structure and multilayer samples, grown using both solid source molecular beam epitaxy (MBE) and gas source chemical vapour deposition (CVD) on Si(100) substrates, have been investigated. These data indicate that each individual layer of Sil-xGex can be uniquely identified with a depth resolution of approximately 3 nm. A comparison of MBE and CVD grown samples has also been made using layers with similar structures and composition and the results compared with conventional Rutherford back-scattering spectrometry (RBS).
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Li, Taotao, Wenjin Gao, Yongsong Wang, Tianzhao Li, Guoxiang Zhi, Miao Zhou i Tianchao Niu. "Thermodynamics and Kinetics in van der Waals Epitaxial Growth of Te". Nanoscale, 2025. https://doi.org/10.1039/d4nr05266h.
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Chemical vapour deposition (CVD) in tube furnace and molecular beam epitaxy (MBE) in vacuum chamber represent the most effective methods for the production of low-dimensional nanomaterials. However, the as-synthesized products...
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Blin, Anna, Alexander Kolar, Andrew Kamen, Qian Lin, Xiaoyang Liu, Aziz Benamrouche, Romain Bachelet i in. "Erbium-doped yttrium oxide thin films grown by chemical vapor deposition for quantum technologies". Applied Physics Reviews 12, nr 1 (1.03.2025). https://doi.org/10.1063/5.0243958.
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The obtention of quantum-grade rare-earth-doped oxide thin films that can be integrated with optical cavities and microwave resonators is of great interest for the development of scalable quantum devices. Among the different growth methods, chemical vapor deposition (CVD) offers high flexibility and has demonstrated the ability to produce oxide films hosting rare-earth ions with narrow linewidths. However, growing epitaxial films directly on silicon is challenging by CVD due to a native amorphous oxide layer formation at the interface. In this manuscript, we investigate the CVD growth of erbium-doped yttrium oxide (Er:Y2O3) thin films on different substrates, including silicon, sapphire, quartz, or yttria stabilized zirconia (YSZ). Alternatively, growth was also attempted on an epitaxial Y2O3 template layer on Si (111) prepared by molecular beam epitaxy (MBE) in order to circumvent the issue of the amorphous interlayer. We found that the substrate impacts the film morphology and the crystalline orientations, with different textures observed for the CVD film on the MBE-oxide/Si template (111) and epitaxial growth on YSZ (001). In terms of optical properties, Er3+ ions exhibit visible and IR emission features that are comparable for all samples, indicating a high-quality local crystalline environment regardless of the substrate. Our approach opens interesting prospects to integrate such films into scalable devices for optical quantum technologies.