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Vapor-phase Epitaxy (vapor-phase + epitaxy)
Selected AbstractsFabrication and Optical Characteristics of Position-Controlled ZnO Nanotubes and ZnO/Zn0.8Mg0.2O Coaxial Nanotube Quantum Structure ArraysADVANCED FUNCTIONAL MATERIALS, Issue 10 2009Jinkyoung Yoo Abstract The position-controlled growth and structural and optical characteristics of ZnO nanotubes and their coaxial heterostructures are reported. To control both the shape and position of ZnO nanotubes, hole-patterned SiO2 growth-mask layers on Si(111) substrates with GaN/AlN intermediate layers using conventional lithography are prepared. ZnO nanotubes are grown only on the hole patterns at 600,°C by catalyst-free metal,organic vapor-phase epitaxy. Furthermore, the position-controlled nanotube growth method allows the fabrication of artificial arrays of ZnO-based coaxial nanotube single-quantum-well structures (SQWs) on Si substrates. In situ heteroepitaxial growth of ZnO and Zn0.8Mg0.2O layers along the circumference of the ZnO nanotube enable an artificial formation of quantum-well arrays in a designed fashion. The structural and optical characteristics of the ZnO nanotubes and SQW arrays are also investigated using synchrotron radiation X-ray diffractometry and photoluminescence and cathodoluminescence spectroscopy. [source] Perfect Bi4Ti3O12 Single-Crystal Films via Flux-Mediated Epitaxy,ADVANCED FUNCTIONAL MATERIALS, Issue 4 2006R. Takahashi Abstract Excellent crystallinity of material films and atomic control of their surface/interface, sufficient for the realization of their optimal physical properties, are technological premises for modern functional-device applications. Bi4Ti3O12 and related compounds attract much interest as highly insulating, ferroelectric materials for use in ferroelectric random-access memories. However, it has been difficult thus far for Bi4Ti3O12 films to satisfy such requirements when formed using vapor-phase epitaxy, owing to the high volatility of Bi in a vacuum. Here, we demonstrate that flux-mediated epitaxy is one of the most promising and widely applicable concepts to overcome this inevitable problem. The key point of this process is the appropriate selection of a multi-component flux system. A combinatorial approach has led to the successful discovery of the novel flux composition of Bi,Cu,O for Bi4Ti3O12 single-crystal film growth. The perfect single-crystal nature of the stoichiometric Bi4Ti3O12 film formed has been verified through its giant grain size and electric properties, equivalent to those of bulk single crystals. This demonstration has broad implications, opening up the possibility of preparing stoichiometric single-crystal oxide films via vapor-phase epitaxy, even if volatile constituents are required. [source] Shape-Controlled Nanoarchitectures Using NanowallsADVANCED MATERIALS, Issue 2 2009Young Joon Hong A novel method for shaping and positioning ZnO nanoarchitectures using conventional lithography and catalyst-free metal organic vapor-phase epitaxy is demonstrated. Nanowalls and nanotubes of desired shapes and arrangements can be grown heteroepitaxially on Si substrates, and their electron-emission characteristics were optimized by changing their diameter and spacing. This method can be readily expanded to create many artificial 1D and 2D structures, as required for various device applications. [source] HVPE GaN substrates: growth and characterizationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010D. Gogova Abstract GaN substrates with low dislocation densities were prepared by halide vapor-phase epitaxy (HVPE) on c-plane sapphire and by means of a post-growth laser-induced lift-off or natural stress-induced (self-) separation process. The HVPE growth on InGaN/GaN buffer layers and subsequent self-separation method was seen as advantageous, in comparison with the laser-induced lift-off one, in terms of lower cost and better crystalline quality of the GaN material obtained. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Examination of intermediate species in GaN metal-organic vapor-phase epitaxy by selective-area growthPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Masakazu Sugiyama Abstract The major reactive intermediate species of GaN has been deduced and its surface reaction rate constant has been obtained through the analysis of multi-scale growth-rate profiles both in the reactor-scale and in the micrometer-scale that were obtained by selective-area growth. Usually, it is difficult to explore surface reaction kinetics, especially for metal-organic vapour phase epitaxy (MOVPE), because of mass-transfer-limited kinetics. This multi-scale analysis, however, has clarified that a single precursor, a gas-phase reaction product between (CH3)3Ga and NH3, leads to the growth of GaN with a surface reaction probability of approximately 0.4 at 1400 K which is a typical growth temperature of GaN. Contribution of higher-order polymers was not significant in growth rate, but they seemed to be a cause of degraded surface morphology. A lumped reaction model of GaN MOVPE was proposed that led to reasonable agreement between a simulated growth-rate profile in the reactor-scale and a corresponding measured profile, which would lead to improved design of reactors and growth conditions. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Analysis of pulsed injection of precursors in AlN-MOVPE growth by computational fluid simulationPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7-8 2010Kenichi Nakamura Abstract We report computational analysis of gas-phase states and main reaction pathways under AlN metalorganic vapor-phase epitaxy (MOVPE) by pulsed injection (PI) method of precursors. Interval times of 0,2 s were inserted between trimethylaluminum (Al(CH3); TMAl) and ammonia (NH3) supply phases to suppress parasitic reactions. In the cases of the interval time of 0 s, polymers and Al-N molecules were dominant species due to parasitic reaction, and the growth species was Al-N molecules generated by TMAl:NH3 pyrolysis. When an interval time was inserted between TMAl and NH3, mixing of TMAl and NH3 were suppressed. Al and NH2 generated from each precursor were dominant species. The main reaction pathway changed from TMAl:NH3 pyrolysis into TMAl pyrolysis with increasing the interval time. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Misfit dislocations and surface morphology of InGaAs/GaAs heterostructures grown by MOVPEPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 8 2009ukasz Gelczuk Abstract A two-dimensional network of misfit dislocations at the interface of the partially relaxed Inx Ga1- xAs epitaxial layers grown on (001)-oriented GaAs substrates by metalorganic vapor-phase epitaxy (MOVPE) has been revealed by transmission electron microscopy (TEM). A close correspondence between the distribution of interfacial misfit dislocations and undulating surface morphology in the form of a characteristic cross-hatch pattern has been observed by means of atomic force microcopy (AFM). Anisotropic strain relaxation attributed to the asymmetry in the formation of misfit dislocations has been also reproduced on the surface in the form of a fine pattern, cutting the cross-hatch one. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Low on-resistance of GaN p-i-n vertical conducting diodes grown on 4H-SiC substratesPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2007Atsushi Nishikawa Abstract We investigated the resistance of conductive AlGaN buffer layers and the current-voltage characteristics of GaN p-i-n vertical conducting diodes on n -type 4H-SiC substrates grown by low-pressure metalorganic vapor-phase epitaxy. High Si doping of the AlGaN buffer layer at the AlGaN/SiC interface produces ohmic current-voltage characteristics in spite of the large band offset between AlGaN and 4H-SiC. Owing to the optimization of the AlGaN buffer layer, a low on-resistance (Ron) of 1.12 m, cm2 with high breakdown voltage (VB) of 300 V is obtained for a GaN p-i-n vertical conducting diode on a 4H-SiC substrate, leading to the figure of merit (VB2/Ron) of 80 MW/cm2, which is larger than that for the diode with the same structure on a 6H-SiC substrate (62 MW/cm2). This result indicates that 4H-SiC is preferable for fabricating GaN-based electronic devices with a low on-resistance and high breakdown voltage. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Morphological evaluation of epitaxial GaN grown on r -plane sapphire by metalorganic vapor-phase epitaxyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 6 2006K. Kusakabe Abstract Morphological evaluation of epitaxial GaN films grown on r -plane sapphire substrates by atmospheric metalorganic vapor-phase epitaxy was investigated. The surface frequently showed rough morphology when the GaN was grown at conventional epitaxial conditions. It was found, however, that the surface roughness was improved by using appropriate combinations of growth temperature and low-temperature GaN buffer thickness. Thereby, a peak-to-valley value of the roughness was reduced from 4 ,m to 0.8 ,m. The rotation of crystallographic orientations was observed in the flattened GaN films. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] The Growth of One-Dimensional Single-Crystalline AlN Nanostructures by HVPE and Their Field Emission Properties,CHEMICAL VAPOR DEPOSITION, Issue 1-3 2010Yun-Ki Byeun Abstract Single-crystalline AlN nanostructures, such as thin films, nanoneedles, nanocolumns, and nanowires, depending on the controlled gas-flow ratio, are synthesized by halide vapor-phase epitaxy (HVPE). In comparison with a typical vapor/liquid/solid (VLS) mechanism for the growth of nanowires, well-aligned AlN nanorod arrays with diameters below 20,nm are grown on a catalyst-free Si substrate though a vapor/solid (VS) mechanism. Their structural and optical properties are measured by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL). In particular, AlN nanorods exhibit an excellent field emission property with a low turn-on field of 2.25,V,µm,1. The field enhancement factor is estimated to be about 784 due to well-aligned, needle-shaped, AlN nanorods. [source] | ||||||||||