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Epitaxy and new stray grain formation mechanism during epitaxial laser melting deposition of Inconel 718 on directionally solidified nickel-based superalloys
摘要： The epitaxy behavior and stray grains (SGs) formation in the deposit during epitaxial laser melting deposition (E-LMD) of directionally solidified (DS) superalloys were investigated. Columnar dendritic structures were obtained by epitaxial solidification on the DS substrate. The deposit also remained the orientation of the substrate. The SGs at the fusion interface, which were hardly eliminated, were attributed to different SGs formation mechanisms. The SGs were divided into GB-SGs and MC-SGs by the distribution characteristics. The GB-SGs at the low-angle and high-angle grain boundaries with a new mechanism of dynamic recrystallization induced by accumulation of thermal strain and stress under repeated spatially variable heating and cooling. The MC-SGs around the carbides were related to the misoriented cellular crystal formation caused by the varied shape of the solid-liquid interface. The columnar to equiaxed transition (CET) was another mechanism of MC-SGs formation.
关键词： Stray grain,Nickel superalloys,Laser metal deposition,Recrystallization,Dynamic,Epitaxy,Microstructure
更新于2025-11-28 14:24:20
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Probing the light hole / heavy hole switching with correlated magneto-optical spectroscopy and chemical analysis on a single quantum dot
摘要： A whole series of complementary studies have been performed on the same, single nanowire containing a quantum dot: cathodoluminescence spectroscopy and imaging, micro-photoluminescence spectroscopy under magnetic field and as a function of temperature, and energy-dispersive X-ray spectrometry and imaging. The ZnTe nanowire was deposited on a Si3N4 membrane with Ti/Al patterns. The complete set of data shows that the CdTe quantum dot features the heavy-hole state as a ground state, although the compressive mismatch strain promotes a light-hole ground state as soon as the aspect ratio is larger than unity (elongated dot). A numerical calculation of the whole structure shows that the transition from the heavy-hole to the light-hole configuration is pushed toward values of the aspect ratio much larger than unity by the presence of a (Zn,Mg)Te shell, and that the effect is further enhanced by a small valence band offset between the semiconductors in the dot and around it.
关键词： molecular beam epitaxy,optical spectroscopy,EDX,semiconductors,cathodoluminescence,quantum dot,nanowires
更新于2025-11-21 11:20:48
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Selective Growth of Ordered Hexagonal InN Nanorods
摘要： Well-ordered and vertically aligned InN nanorods with high aspect ratio are synthetized by hydride vapor phase epitaxy (HVPE) using the selective area growth (SAG) approach. The growth occurs through the apertures of a SiNx masked Ga-polar GaN/c-Al2O3 template for adjusted growth temperature and V/III ratio. The nanorods exhibit a hexagonal shape without any rotation around the growth axis. The wurtzite structure and the high crystalline quality of InN nanorods are confirmed by X-ray diffraction (XRD) as well as by high-resolution transmission electron microscopy (HR-TEM). Only few stacking faults are identified at the bottom part of the nanorods. Photoluminescence (PL) displays an emission peak centered at 0.77 eV which agrees with the band gap of InN. These promising achievements, which go far beyond the existing InN growth limitations, pave the way towards the integration of pure InN in future devices
关键词： Selective Area Growth,Hydride Vapor Phase Epitaxy,Indium Nitride,Nanorods
更新于2025-11-21 11:03:13
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Ferroelectric Enhanced Performance of a GeSn/Ge Dual-Nanowire Photodetector
摘要： GeSn offers a reduced bandgap than Ge and has been utilized in Si-based infrared photodetectors with extended cutoff wavelength. However, traditional GeSn/Ge heterostructure usually consists defects like misfit dislocations due to the lattice mismatch issue. The defects with the large feature size of photodetector fabricated on bulk GeSn/Ge heterostructure induces considerable dark current. Here, we demonstrate a flexible GeSn/Ge dual-nanowire (NW) structure, in which the strain relaxation is achieved by the elastic deformation without introducing defects and the feature dimension is naturally at nanoscale. Photodetector with low dark current can be built on GeSn/Ge dual-NW, which exhibits an extended detection wavelength beyond 2 μm and the enhanced responsivity compared to Ge NW. Moreover, the dark current can be further suppressed by the depletion effect from ferroelectric polymer side gate. Our work suggests the flexible GeSn/Ge dual-NW may open an avenue for Si-compatible optoelectronic circuits operating in the short-wavelength infrared range.
关键词： Nanowire,Germanium-tin,Molecular beam epitaxy (MBE),Side-gated,Photodetector,Ferroelectrical polymer
更新于2025-11-21 11:01:37
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Tuning of the Optical Properties of the Transparent Conducting Oxide SrVO <sub/>3</sub> by Electronic Correlations
摘要： The vanadate SrVO3 is a transparent conductor perovskite with optical and electrical properties competing with those of the most-used indium tin oxide material. Although its charge density is comparable to that of metals, SrVO3 shows a plasma frequency below the visible range due to strong electronic correlations characterizing the electronic transport in this material and enhancing the effective mass. Therefore, the well-known interplay between the structure and the electronic properties of strongly correlated systems can be used in such transparent conductor to tune the optical properties, as the plasma frequency also depends on the effective mass. In this study, SrVO3 films are grown by pulsed laser deposition onto different lattice mismatched perovskite substrates such as SrTiO3, LaAlO3, and (LaAlO3)0.3(Sr2TaAlO6)0.7 at different growth temperatures. The structural, electronic, and optical properties are analyzed, illustrating the influence of the strain on the structure of the films and on a shift of the plasma frequency. The electronic correlations in this new group of transparent conducting oxides can be therefore used as a supplementary lever for the tuning of the functional properties.
关键词： transparent conducting oxides,vanadates,thin films,correlated materials,epitaxy
更新于2025-10-22 19:40:53
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Nanoscale GaN Epilayer Grown by Atomic Layer Annealing and Epitaxy at Low Temperature
摘要： Heteroepitaxy with large thermal and lattice mismatch between the semiconductor and substrate is a critical issue for high-quality epitaxial growth. Typically, high growth temperatures (>1000 °C) are required to achieve high-quality GaN epilayers by conventional metal?organic chemical vapor deposition. In this study, the high-quality GaN heteroepitaxy is realized by atomic layer annealing and epitaxy (ALAE) at a low growth temperature of 300 °C. The layer-by-layer, in situ He/Ar plasma treatment at a low plasma power was introduced in each cycle of atomic layer deposition to contribute the e?ective annealing e?ect for signi?cant enhancement of the GaN crystal quality. The Penning e?ect is responsible for signi?cant improvement of the GaN crystal quality due to the incorporation of He into the Ar plasma. The high-resolution transmission electron microscopy, nano-beam electron di?raction, and atomic force microscopy reveal a high-quality nanoscale single-crystal GaN heteroepitaxy and a very smooth surface. The full width at half-maximum of the X-ray rocking curve of the GaN epilayer is as low as 168 arcsec. The low-temperature ALAE technique is highly bene?cial to grow high-quality nanoscale GaN epilayers for sustainable, energy-saving, and energy-e?cient devices including high-performance solid-state lighting, solar cells, and high-power electronics.
关键词： Atomic layer annealing,Atomic layer deposition,Gallium nitride,Atomic layer epitaxy,Plasma treatment
更新于2025-09-23 15:23:52
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Uniformity and repeatability of InAlN-barrier HEMTs growth by high-speed-rotation single-wafer MOCVD tool
摘要： We fabricated high-electron-mobility transistor structures with InAlN as a barrier layer on 8- or 6-inch Si substrates by using a recently developed high-speed-wafer-rotation single-wafer MOCVD tool. It has been reported that Ga inclusion in the InAlN layer causes serious problems in the control of group III metal composition in some cases, but the samples grown using the tool exhibited an InAlN layer with an abrupt interface and almost no Ga inclusion. Excellent in-wafer uniformity, repeatability, and wafer-to-wafer uniformity of device structure are also reported. The results shown in this paper indicate high performance of the tool in the real production of devices.
关键词： A3. Metalorganic vapor phase epitaxy,B1. Nitrides,B2. Semiconducting III-V materials,B3. High electron mobility transistors
更新于2025-09-23 15:23:52
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Optical and interface characteristics of Al0.56Ga0.44N/Al0.62Ga0.38N multiquantum wells with ～280?nm emission grown by plasma-assisted molecular beam epitaxy
摘要： We have investigated the nature of Al0.56Ga0.44N/Al0.62Ga0.38N multiquantum wells grown by plasma-assisted molecular beam epitaxy for application in deep-ultraviolet light emitters. Excitation and temperature-dependent and time-resolved photoluminescence measurements and transmission and reflectance spectroscopy have been complemented by high-angle annular dark field scanning transmission electron microscopy. The 3nm quantum wells are characterized by interface roughness having a height of 0.3-1nm and the maximum value is in excellent agreement with values obtained from calculations done to analyze the measured photoluminescence lineshape. The radiative lifetime increases with temperature, suggesting the role of electron-hole scattering to cool photoexcited carriers to the ground state of the quantum wells.
关键词： A1. Interfaces,B1. Nitrides,A3. Quantum wells,A3. Molecular beam epitaxy
更新于2025-09-23 15:23:52
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Growth, morphology and crystal structure of electrodeposited Bi2Se3 films: Influence of the substrate
摘要： In this study, we investigated the growth, morphology and crystal structure of electrodeposited Bi2Se3 films on n-Si, Au and Ru substrates. The range of potentials at which films with good quality and stoichiometry can be grown have been identified. Scanning electron micrographs of the early stages of nucleation and growth suggests the film formation on all three substrates follow the Volmer-Weber growth mode. In the case of Si substrate, a pure orthorhombic phase of Bi2Se3 could be grown which is influenced by the epitaxy of the Si substrate. The Faradaic efficiency of film growth on Si substrate was found to be around 90%. However, on Au and Ru substrates, growth of mainly the rhombohedral phase could be achieved having relatively lower Faradaic efficiencies of 68% and 78%, respectively. The Bi2Se3 films grown on Au at more negative potentials were found to exhibit improvements in the rhombohedral crystal phase. Low temperature annealing was found to transform the orthorhombic or mixed phase crystal structure to that of pure rhombohedral. The onset of phase transformation in the mixed phase Bi2Se3 films (on Au) was found to be around 125°C, determined using in-situ Raman spectroscopy. Aside from the temperature, the duration of heat treatment is identified to play a crucial role in this phase transformation. Based on our findings on room temperature deposition, we conclude that the growth of pure orthorhombic phase is favored on Si, while on Au and Ru, growth of the rhombohedral or mixed phase of Bi2Se3 could be achieved.
关键词： Raman,Annealing,Electrodeposition,Crystal structure,Substrate epitaxy,Bi2Se3,Growth
更新于2025-09-23 15:23:52
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High throughput MOVPE and accelerated growth rate of GaAs for PV application
摘要： We present the feasibility of metalorganic vapor phase epitaxy (MOVPE) with extremely high-speed growth of GaAs for solar cell applications. The growth rate was increased up to 120 μm/h, and exhibited an almost linear relationship with the amount of supplied trimethylgallium (TMGa). The thickness variation and doped carrier concentration of GaAs grown at 90 μm/h were comparable to those of conventionally grown GaAs at a lower growth rate. The potential for reducing the V/III supply ratio was investigated to reduce the material cost. Non-doped GaAs wafers were grown at the accelerated growth rate of 90 μm/h, with various V/III ratios. The growth rate of GaAs increased by 20% when the V/III ratio was decreased from 40 to 5. In low temperature photo-luminescence (PL) measurement, significant change in PL spectra was not observed, indicating that there was no significant change in quality. The light-power conversion efficiency was almost comparable for V/III ratios from 10 to 40 whereas that at the lowest V/III ratio of 5 was degraded. Photovoltaic (PV) solar cells of GaAs were fabricated with various growth condition. It is found that the performance of the cells grown at 90 μm/h were comparable with previous results.
关键词： A3. Metalorganic vapor phase epitaxy,B2. Semiconducting GaAs,B3. Solar cells,A1. Crystal morphology
更新于2025-09-23 15:23:52