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European Microscopy Congress 2016: Proceedings || Microstructural evolution and thermal stability of nitride-based metal/semiconductor superlattices for thermoelectric and hard-coating applications
摘要： A detailed analysis on the quality and microstructure of various metal/semiconductor superlattices employing HR(S)/TEM (high-resolution (scanning)/transmission electron microscopy) imaging and energy dispersive x-ray spectroscopy (EDX) mapping on as-deposited and annealed samples is presented. Epitaxial metal/semiconductor superlattices are known to be promising candidates for compounds in electronic, photonic, and plasmonic devices, but are also of interest for applications as hard coatings, and in thermoelectric materials [1]. The crystalline quality of the superlattices, in terms of their defect density, phase purity, interface roughness, and stoichiometry of the individual layers, plays a crucial role with respect to the physical properties and thus the applicability of such superlattice stacks. It was recently shown that metal/semiconductor superlattices based on (Al,Sc)N as the semiconductor component can be grown epitaxially with low-defect densities by magnetron sputtering on [001]MgO substrates [2]. Phase formation and thermal stability studies of as-deposited and long-time annealed cubic TiN/(Al,Sc)N superlattices employing a combination of HR(S)/TEM and EDX mapping revealed intermixing of the TiN and (Al,Sc)N layers by interdiffusion of the metal atoms with increased annealing time [3]. Improved (Ti,W)N/(Al,Sc)N [4] and (Hf,Zr)N/ScN [5] superlattices were grown by magnetron sputtering and analyzed with various TEM methods, and their microstructural evolution as well as thermal stability becomes presented here. An example is show in Figure 1, which shows an overview of an improved cubic (Ti,W)N/(Al,Sc)N superlattice stack in cross-section STEM (a), and a typical HRTEM micrograph of the metal/semiconductor interface region, demonstrating the high epitaxial quality of the growth [4]. Figure 2 demonstrates the superior thermal stability of the (Zr,Hf)N- based systems as compared to previous TiN- based superlattices. EDX mapping at high-resolution before and after annealing at 950 °C for 120 hours reveals diffusion of the metal atoms in the TiN/AlScN system (b), while the Hf0.5Zr0.5N/ScN superlattice stays intact (d). All experiments were conducted at Link?ping’s image- and probe-corrected and monochromated FEI Titan3 60-300 microscope equipped with a Gatan Quantum ERS GIF, high-brightness XFEG source, and Super-X EDX detector, operated at 300 kV [6].
关键词： Nitrides,superlattices,EDX mapping
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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Transparent Ta3N5 Photoanodes for Efficient Oxygen Evolution toward the Development of Tandem Cells
摘要： Photoelectrochemical water splitting is regarded as a promising approach to the production of hydrogen, and the development of efficient photoelectrodes is one aspect of realizing practical systems. In this work, transparent Ta3N5 photoanodes were fabricated on n-type GaN/sapphire substrates to promote O2 evolution in tandem with a photocathode, to realize overall water splitting. Following the incorporation of an underlying GaN layer, a photocurrent of 6.3 mA cm-2 was achieved at 1.23 V vs. a reversible hydrogen electrode. The transparency of Ta3N5 to wavelengths longer than 600 nm allowed incoming solar light to be transmitted to a CuInSe2 (CIS), which absorbs up to 1100 nm. A stand-alone tandem cell with a serially-connected dual-CIS unit terminated with a Pt/Ni electrode was thus constructed for H2 evolution. This tandem cell exhibited a solar-to-hydrogen energy conversion efficiency greater than 7% at the initial stage of the reaction.
关键词： solar energy conversion,photoelectrochemistry,water splitting,photoelectrochemical tandem cell,(oxy)nitrides
更新于2025-09-23 15:22:29
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Fabrication of AlN templates on SiC substrates by sputtering-deposition and high-temperature annealing
摘要： High-quality AlN templates fabricated by sputtering-deposition and post-deposition high-temperature annealing have great potential for deep ultraviolet light-emitting device applications. In this work, we fabricated AlN films on 6H-SiC substrates by sputtering and face-to-face annealing and characterized the structural quality of the AlN films before and after annealing. As reported in previous studies, to accomplish high-quality AlN films on SiC substrates using conventional methods, such as molecular beam epitaxy or metalorganic vapor phase epitaxy (MOVPE), it is important to grow the AlN on the SiC coherently. However, in this work, although the annealed AlN films were fully relaxed from the SiC substrates, or even had tensile strain, the AlN films indicated high crystallinity. The X-ray rocking curve full width at half maximum (XRC-FWHM) values of the 200-nm-thick annealed AlN film were 17 and 246 arcsec for the AlN (0002) and (10–12) diffraction, respectively. Though the annealed AlN film indicated rough surfaces with bunched step structures, the surface morphology was remarkably improved by MOVPE growth and clear atomic step-and-terrace structures were formed. The XRC-FWHM values of the MOVPE-grown AlN were 90 and 239 arcsec for the AlN (0002) and (10–12) diffraction, respectively.
关键词： A1. Stresses,A1. Atomic force microscopy,B1. Nitrides,B2. Semiconducting III-V materials,A1. X-ray diffraction
更新于2025-09-23 15:22:29
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Strain control of GaN grown on Si substrates using an AlGaN interlayer
摘要： To suppress wafer bowing and crack generation of GaN on Si substrates, we investigated the effects of the Al content and thickness of the AlGaN interlayer on the compressive strain in the overlying GaN layer theoretically and experimentally. In the simulation, AlGaN relaxes gradually over the critical thickness. Therefore, the relaxation ratio of AlGaN at the top surface can be defined as a function of Al content and thickness. Too high Al content or too thick AlGaN interlayer induced too large initial strain in the upper GaN layer, which caused rapid and succeeding gradual relaxation, i.e., decrease of strain, of the GaN layer during growth because of generation of threading dislocations. Conversely, low Al content or thin AlGaN interlayer could induce constant but only small strain in the GaN layer. Therefore, the ideal relaxation ratio of the AlGaN surface exists to apply the maximal constant compressive strain in the GaN layer. The relaxation ratios of AlGaN interlayers determined in experiments were much smaller than those calculated in the simulation. Although the measured compressive strain in the GaN layer was smaller than expected, its decrease rate was small when grown on AlGaN interlayers with an almost ideal relaxation ratio.
关键词： Computer simulation,Characterization,Metalorganic vapor phase epitaxy,Stresses,Growth models,Nitrides
更新于2025-09-23 15:22:29
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Rivalry Under Pressure - The Coexistence of Ambient-pressure Motifs and Close-packing in Silicon Phosphorus Nitride Imide SiP2N4NH
摘要： Non-metal nitrides such as BN, Si3N4 and P3N5 meet numerous demands on high-performance materials and their high-pressure polymorphs exhibit outstanding mechanical properties. Herein, we present the silicon phosphorus nitride imide SiP2N4NH featuring six-fold coordinated Si. Using the multianvil technique, SiP2N4NH was obtained from high-pressure high-temperature synthesis at 8 GPa and 1100 °C with in situ formed HCl acting as a mineralizer. Its structure was elucidated by combination of single-crystal X-ray diffraction and solid-state NMR measurements. Moreover, SiP2N4NH was characterized by energy-dispersive X-ray spectroscopy and (temperature-dependent) powder X-ray diffraction. The highly condensed Si/P/N framework features PN4 tetrahedra as well as the rare motif of SiN6 octahedra and is discussed in the context of ambient-pressure motifs competing with close-packing of nitride anions, representing a missing link in high-pressure chemistry of non-metal nitrides.
关键词： nitrides,silicon,high-pressure chemistry,phosphorus,solid-state structures
更新于2025-09-23 15:22:29
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Ordered Mesoporous C?N? with a Combined Triazole and Triazine Framework and Its Graphene Hybrids
摘要： Mesoporous carbon nitrides (MCN) with C3N4 stoichiometry could find applications in fields ranging from catalysis, sensing, and adsorption–separation to biotechnology. The extension of the synthesis of MCN with different nitrogen contents and chemical structures promises access to even a wide range of applications. Here we show mesoporous C3N5 with a combined triazole and triazine framework prepared via a simple self-assembly of 5-amino-1H-tetrazole (5-ATTZ). We are able to hybridize these nanostructures with graphene by using graphene–mesoporous silica hybrids as a template to tune the electronic properties. Density functional theory calculations in combination with various spectroscopic analyses clearly demonstrate that the C3N5 consists of 1 triazole and 2 triazine moieties. The triazole-based mesoporous C3N5 and its graphene hybrids are found to be highly active for oxygen reduction reaction (ORR) with a higher diffusion-limiting current density and a decreased overpotential than those of bulk g-C3N4. We expect that this simple approach to the triazole-based mesoporous C3N5 could be extended for the preparation of series of new class of MCN nanostructures and their hybrids.
关键词： oxygen reduction reaction,porous materials,electrocatalysts,N-rich carbon nitrides,structure
更新于2025-09-23 15:21:21
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Buried defects induced by plasma assisted molecular beam epitaxy of AlN and GaN on Silicon
摘要： The present work is dedicated to the study of peculiar defects observed in GaN/AlN structures grown on Silicon substrate using the plasma assisted Molecular Beam Epitaxy under metal-rich conditions. Optical microscopy shows that these defects have unde?ned shape when AlN is grown on Silicon. On the contrary such defects are not observed with AlN ?lms grown under nitrogen-rich plasma assisted or ammonia source Molecular Beam Epitaxy, but triangular shape defects appear in case of GaN regrowth on the latter. As scanning electron microscopy is not able to evidence these defects but only protuberances connected with them, we deduce that they are located in the Silicon substrate. Complementary analysis with atomic force microscopy and energy dispersive X-ray analysis lead us to propose a scenario involving the etching of the Silicon substrate with Ga or Al di?using through weak points in the nucleation layer.
关键词： A1. Defects,B1. Nitrides on Silicon,A3. Molecular beam epitaxy,B2. Semiconducting materials
更新于2025-09-23 15:21:21
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Photothermal Transduction Efficiencies of Plasmonic Group 4 Metal Nitride Nanocrystals
摘要： The photothermal transduction e?ciencies of group 4 metal nitrides, TiN, ZrN, and HfN, at λ = 850 nm are reported, and the performance of these materials is compared to an Au nanorod benchmark. Transition metal nitride nanocrystals with an average diameter of ～15 nm were prepared using a solid-state metathesis reaction. HfN exhibited the highest photothermal transduction e?ciency of 65%, followed by ZrN (58%) and TiN (49%), which were all higher than those of the commercially purchased Au nanorods (43%). Computational studies performed using a ?nite element method showed HfN and Au to have the lowest and highest scattering cross section, respectively, which could be a contributing factor to the e?ciency trends observed. Furthermore, the changes in temperature as a function of illumination intensity and solution concentration, as well as the cycling stability of the metal nitride solutions, were studied in detail.
关键词： nanocrystals,plasmonic,photothermal transduction,metal nitrides,Au nanorods
更新于2025-09-23 15:21:01