Showing papers on "Epitaxy published in 2019"
TL;DR: Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation, and the resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates.
Abstract: The propensity of metals to form irregular and nonplanar electrodeposits at liquid-solid interfaces has emerged as a fundamental barrier to high-energy, rechargeable batteries that use metal anodes. We report an epitaxial mechanism to regulate nucleation, growth, and reversibility of metal anodes. The crystallographic, surface texturing, and electrochemical criteria for reversible epitaxial electrodeposition of metals are defined and their effectiveness demonstrated by using zinc (Zn), a safe, low-cost, and energy-dense battery anode material. Graphene, with a low lattice mismatch for Zn, is shown to be effective in driving deposition of Zn with a locked crystallographic orientation relation. The resultant epitaxial Zn anodes achieve exceptional reversibility over thousands of cycles at moderate and high rates. Reversible electrochemical epitaxy of metals provides a general pathway toward energy-dense batteries with high reversibility.
855 citations
TL;DR: Optical spectroscopy measurements on atomically thin epitaxial hBN are performed providing indications of the presence of a direct gap of energy 6.1 eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit.
Abstract: Hexagonal boron nitride is a large band-gap insulating material which complements the electronic and optical properties of graphene and the transition metal dichalcogenides. However, the intrinsic optical properties of monolayer boron nitride remain largely unexplored. In particular, the theoretically expected crossover to a direct-gap in the limit of the single monolayer is presently not confirmed experimentally. Here, in contrast to the technique of exfoliating few-layer 2D hexagonal boron nitride, we exploit the scalable approach of high-temperature molecular beam epitaxy to grow high-quality monolayer boron nitride on graphite substrates. We combine deep-ultraviolet photoluminescence and reflectance spectroscopy with atomic force microscopy to reveal the presence of a direct gap of energy 6.1 eV in the single atomic layers, thus confirming a crossover to direct gap in the monolayer limit. Insulating hexagonal boron nitride (hBN) is theoretically expected to undergo a crossover to a direct bandgap in the monolayer limit. Here, the authors perform optical spectroscopy measurements on atomically thin epitaxial hBN providing indications of the presence of a direct gap of energy 6.1 eV in the single atomic layer.
167 citations
TL;DR: In this article, high crystalline quality with pure β-phase (AlxGa1−x)2O3 was achieved for films with Al composition x < 27%, while a higher Al composition induced phase segregation which was observed via X-ray diffraction spectra.
Abstract: (010) β-(AlxGa1−x)2O3 thin films were grown on (010) β-Ga2O3 substrates via metalorganic chemical vapor deposition with up to 40% Al incorporation by systematic tuning of the Trimethylaluminum (TMAl)/triethylgallium molar flow rate ratio and growth temperature. High crystalline quality with pure β-phase (AlxGa1−x)2O3 was achieved for films with Al composition x < 27%, while a higher Al composition induced phase segregation which was observed via X-ray diffraction spectra. Al incorporation was highly dependent on the growth temperature, chamber pressure, oxygen partial pressure, and TMAl molar flow rate. Atomic resolution scanning transmission electron microscopy (STEM) imaging demonstrated a high crystalline quality β-(Al0.15Ga0.85)2O3 film with an epitaxial interface. High resolution STEM imaging of (AlxGa1−x)2O3/Ga2O3 superlattice (SL) structures revealed superior crystalline quality for the 23% Al composition. When the Al composition reaches 40%, the SL structure maintained the β-phase, but the interfaces became rough with inhomogeneous Al distribution. N-type doping using Si in β-(AlxGa1−x)2O3 films with the Al composition up to 33.4% was demonstrated.
97 citations
TL;DR: In this article, the structural quality of the orthorhombic Ga2O3 thin film was studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps.
Abstract: High-quality Ga2O3 thin films in the orthorhombic κ-phase are grown by pulsed-laser deposition using a tin containing target on c-sapphire, MgO(111), SrTiO3(111), and yttria-stabilized ZrO2(111) substrates. The structural quality of the layers is studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps. Our layers exhibit superior crystalline properties in comparison to thin films deposited in the monoclinic β-phase at nominally identical growth parameters. Furthermore, the surface morphology is significantly improved and the root-mean-squared roughness of the layers was as low as ≈0.5 nm, on par with homoepitaxial β-Ga2O3 thin films in the literature. The orthorhombic structure of the thin films was evidenced, and the epitaxial relationships were determined for each kind of the substrate. A tin-enriched surface layer on our thin films measured by depth-resolved photoelectron spectroscopy suggests surfactant-mediated epitaxy as a possible growth mechanism. Thin films in the κ-phase are a promising alternative for β-Ga2O3 layers in electronic and optoelectronic device applications.High-quality Ga2O3 thin films in the orthorhombic κ-phase are grown by pulsed-laser deposition using a tin containing target on c-sapphire, MgO(111), SrTiO3(111), and yttria-stabilized ZrO2(111) substrates. The structural quality of the layers is studied based on the growth parameters employing X-ray diffraction 2θ-ω scans, rocking curves, ϕ scans, and reciprocal space maps. Our layers exhibit superior crystalline properties in comparison to thin films deposited in the monoclinic β-phase at nominally identical growth parameters. Furthermore, the surface morphology is significantly improved and the root-mean-squared roughness of the layers was as low as ≈0.5 nm, on par with homoepitaxial β-Ga2O3 thin films in the literature. The orthorhombic structure of the thin films was evidenced, and the epitaxial relationships were determined for each kind of the substrate. A tin-enriched surface layer on our thin films measured by depth-resolved photoelectron spectroscopy suggests surfactant-mediated epitaxy as a pos...
87 citations
Patent•
TSMC1
TL;DR: A semiconductor device includes a plurality of semiconductor fins, an epitaxy structure, a capping layer, and a contact as discussed by the authors, which is in contact with the epitaxy and the capping.
Abstract: A semiconductor device includes a plurality of semiconductor fins, an epitaxy structure, a capping layer, and a contact. The epitaxy structure adjoins the semiconductor fins. The epitaxy structure has a plurality of protrusive portions. The capping layer is over a sidewall of the epitaxy structure. The contact is in contact with the epitaxy structure and the capping layer. The contact has a portion between the protrusive portions. The portion of the contact between the protrusive portions has a bottom in contact with the epitaxy structure.
77 citations
TL;DR: In this paper, α-Ga2O3 homoepitaxial films were grown on commercially available c-plane sapphire substrates, and the film morphology was found to be strongly impacted by the surface finish of the substrate.
Abstract: Halide vapor phase epitaxy was used to grow homoepitaxial films of β-Ga2O3 on bulk (010) crystals and heteroepitaxial films of α-Ga2O3 on c-plane sapphire substrates. The β-Ga2O3 substrates were prepared prior to growth to remove sub-surface damage and to apply various miscuts to their surfaces. Structural and electrical properties were found to be most impacted by the crystallinity of the β-Ga2O3 substrate itself, while the surface morphology was found to be most impacted by the miscut of the substrate. The appropriate choice of growth conditions and the miscut appear to be critical to realizing smooth, thick (>20 µm) homoepitaxial films of β-Ga2O3. The α-Ga2O3 films were grown on commercially available c-plane sapphire substrates, and the film morphology was found to be strongly impacted by the surface finish of the sapphire substrates. The α-Ga2O3 films were found to be smooth and free of additional phases or crystal twinning when the sapphire was sufficiently polished prior to growth.
77 citations
TL;DR: In this article, the growth of high quality AlN films on nano-patterned sapphire substrates (NPSSs) by graphene-assisted quasi-van der Waals epitaxy, which enables rapid coalescence to shorten the growth time.
Abstract: We report the growth of high-quality AlN films on nano-patterned sapphire substrates (NPSSs) by graphene-assisted quasi-van der Waals epitaxy, which enables rapid coalescence to shorten the growth time. Due to the presence of graphene (Gr), AlN tends to be two-dimensional laterally expanded on the NPSS, leading to the reduction of dislocation density and strain release in the AlN epitaxial layer. Using first-principles calculations, we confirm that Gr can reduce the surface migration barrier and promote the lateral migration of metal Al atoms. Furthermore, the electroluminescence results of deep ultraviolet light emitting diodes (DUV-LEDs) have exhibited greatly enhanced emission located at 280 nm by inserting the Gr interlayer. The present work may provide the potential to solve the bottleneck of high efficiency DUV-LED.
76 citations
TL;DR: The observation of a polarization-induced high-density 2D hole gas in epitaxially grown gallium nitride on aluminium nitride is reported and it is shown that such hole gases can form without acceptor dopants.
Abstract: A high-conductivity two-dimensional (2D) hole gas, analogous to the ubiquitous 2D electron gas, is desirable in nitride semiconductors for wide-bandgap p-channel transistors. We report the observation of a polarization-induced high-density 2D hole gas in epitaxially grown gallium nitride on aluminium nitride and show that such hole gases can form without acceptor dopants. The measured high 2D hole gas densities of about 5 × 1013 per square centimeters remain unchanged down to cryogenic temperatures and allow some of the lowest p-type sheet resistances among all wide-bandgap semiconductors. The observed results provide a probe for studying the valence band structure and transport properties of wide-bandgap nitride interfaces.
75 citations
TL;DR: In this article, the epitaxial lateral overgrowth of α-Ga2O3 by halide vapor phase epitaxy was demonstrated, where patterned SiO2 masks were prepared on a (0001) α-G 2 O 3/sapphire template, and then α-GA 2O 3 islands were regrown selectively on the mask windows.
Abstract: We demonstrate the epitaxial lateral overgrowth of α-Ga2O3 by halide vapor phase epitaxy. We prepared patterned SiO2 masks on a (0001) α-Ga2O3/sapphire template, and then α-Ga2O3 islands were regrown selectively on the mask windows. The islands grew vertically and laterally to coalesce with each other. Facet control of the α-Ga2O3 islands was achieved by controlling the growth temperature, and inclined facets developed by decreasing the temperature. Transmission electron microscopy revealed that the crystal quality of the regrown α-Ga2O3 was improved owing to both the blocking of dislocations by the mask and the dislocation bending by the inclined facets.
74 citations
70 citations
TL;DR: A new approach for the fabrication of ultraflat single-crystal graphene using Cu/Ni (111)/sapphire wafers at lower temperature is reported and it is found that the temperature of epitaxial growth of graphene usingCu/ Ni (111) can be reduced to 750 °C, much lower than that of earlier reports on catalytic surfaces.
Abstract: The future electronic application of graphene highly relies on the production of large-area high-quality single-crystal graphene. However, the growth of single-crystal graphene on different substrates via either single nucleation or seamless stitching is carried out at a temperature of 1000 °C or higher. The usage of this high temperature generates a variety of problems, including complexity of operation, higher contamination, metal evaporation, and wrinkles owing to the mismatch of thermal expansion coefficients between the substrate and graphene. Here, a new approach for the fabrication of ultraflat single-crystal graphene using Cu/Ni (111)/sapphire wafers at lower temperature is reported. It is found that the temperature of epitaxial growth of graphene using Cu/Ni (111) can be reduced to 750 °C, much lower than that of earlier reports on catalytic surfaces. Devices made of graphene grown at 750 °C have a carrier mobility up to ≈9700 cm2 V-1 s-1 at room temperature. This work shines light on a way toward a much lower temperature growth of high-quality graphene in single crystallinity, which could benefit future electronic applications.
TL;DR: This work investigates the thin-film growth of a heterostructure stack comprised of n-type β-Ga2O3 and p-type cubic NiO layers grown consecutively on c-plane sapphire using pulsed laser deposition, as well as the fabrication of solar-blind ultraviolet-C photodetectors based on the resulting p-n junction heterodiodes.
Abstract: In recent years, β-Ga2O3/NiO heterojunction diodes have been studied, but reports in the literature lack an investigation of an epitaxial growth process of high-quality single-crystalline β-Ga2O3/NiO thin films via electron microscopy analysis and the fabrication and characterization of an optoelectronic device based on the resulting heterojunction stack. This work investigates the thin-film growth of a heterostructure stack comprising n-type β-Ga2O3 and p-type cubic NiO layers grown consecutively on c-plane sapphire using pulsed laser deposition, as well as the fabrication of solar-blind ultraviolet-C photodetectors based on the resulting p-n junction heterodiodes. Several characterization techniques were employed to investigate the heterostructure, including X-ray crystallography, ion beam analysis, and high-resolution electron microscopy imaging. X-ray diffraction analysis confirmed the single-crystalline nature of the grown monoclinic and cubic (201) β-Ga2O3 and (111) NiO films, respectively, whereas electron microscopy analysis confirmed the sharp layer transitions and high interface qualities in the NiO/β-Ga2O3/sapphire double-heterostructure stack. The photodetectors exhibited a peak spectral responsivity of 415 mA/W at 7 V reverse-bias voltage for a 260 nm incident-light wavelength and 46.5 pW/μm2 illuminating power density. Furthermore, we also determined the band offset parameters at the thermodynamically stable heterointerface between NiO and β-Ga2O3 using high-resolution X-ray photoelectron spectroscopy. The valence and conduction band offsets values were found to be 1.15 ± 0.10 and 0.19 ± 0.10 eV, respectively, with a type-I energy band alignment.
TL;DR: An engineering strategy to surmount strain-induced difficulties in the growth achieving highly strained cores with a sizeable change in their band gap is reported, rendering gallium arsenide nanowires suitable for photonic devices across the near-infrared range.
Abstract: The realisation of photonic devices for different energy ranges demands materials with different bandgaps, sometimes even within the same device. The optimal solution in terms of integration, device performance and device economics would be a simple material system with widely tunable bandgap and compatible with the mainstream silicon technology. Here, we show that gallium arsenide nanowires grown epitaxially on silicon substrates exhibit a sizeable reduction of their bandgap by up to 40% when overgrown with lattice-mismatched indium gallium arsenide or indium aluminium arsenide shells. Specifically, we demonstrate that the gallium arsenide core sustains unusually large tensile strain with hydrostatic character and its magnitude can be engineered via the composition and the thickness of the shell. The resulted bandgap reduction renders gallium arsenide nanowires suitable for photonic devices across the near-infrared range, including telecom photonics at 1.3 and potentially 1.55 μm, with the additional possibility of monolithic integration in silicon-CMOS chips. Designing core/shell nanowires with desired optoelectronic properties of III-V semiconductor alloys remains a challenge. Here, the authors report an engineering strategy to surmount strain-induced difficulties in the growth achieving highly strained cores with a sizeable change in their band gap.
TL;DR: High quality GaAs and GaInP are shown at rates exceeding 300 and 200 micrometers per hour by dynamic hydride vapor phase epitaxy and 25% efficient solar cells, indicating that high material quality can be maintained at these extremely high growth rates.
Abstract: We report gallium arsenide (GaAs) growth rates exceeding 300 µm h−1 using dynamic hydride vapor phase epitaxy. We achieved these rates by maximizing the gallium to gallium monochloride conversion efficiency, and by utilizing a mass-transport-limited growth regime with fast kinetics. We also demonstrate gallium indium phosphide growth at rates exceeding 200 µm h−1 using similar growth conditions. We grew GaAs solar cell devices by incorporating the high growth rate of GaAs and evaluated its material quality at these high rates. Solar cell growth rates ranged from 35 to 309 µm h−1 with open circuit voltages ranging from 1.04 to 1.07 V. The best devices exceeded 25% efficiency under the AM1.5 G solar spectrum. The high open-circuit voltages indicate that high material quality can be maintained at these extremely high growth rates. These results have strong implications toward lowering the deposition cost of III-V materials potentially enabling the deposition of high efficiency devices in mere seconds. Gallium arsenide holds record efficiency for single junction solar cells, but high production costs limit applications. Here Metaferia et al. show high quality GaAs and GaInP at rates exceeding 300 and 200 micrometers per hour by dynamic hydride vapor phase epitaxy and > 25% efficient solar cells.
TL;DR: In this paper, n-type degenerate doping in β-(Al0.26Ga0.74)2O3 epitaxial thin films grown by metalorganic vapor-phase epitaxy and modulation doping was reported.
Abstract: We report on n-type degenerate doping in β-(Al0.26Ga0.74)2O3 epitaxial thin films grown by metalorganic vapor-phase epitaxy and modulation doping in β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructures. Alloy composition is confirmed using high-resolution X-ray diffraction measurements. Carrier concentration in the thin films is proportional to the silane molar flow. Room-temperature Hall measurements showed a high carrier concentration of 6 × 1018 cm–3 to 7.3 × 1019 cm−3 with a corresponding electron mobility between 53–27 cm2 V–1 s–1 in uniformly doped β-(Al0.26Ga0.74)2O3 layers. Modulation doping is used to realize a total electron sheet charge of 2.3 × 1012 cm−2 in a β-(Al0.26Ga0.74)2O3/β-Ga2O3 heterostructure using a uniformly doped β-(Al0.26Ga0.74)2O3 barrier layer and a thin spacer layer.
TL;DR: In this article, atomic layer deposition was applied to grow TiO2 thin films containing anatase, rutile and mixture of TiO 2-II and R 2-III phases with the aim of investigating the dependence of optical parameters on the formation of metastable Ti2-II phase.
TL;DR: Improved MOVPE growth conditions for the different Ga2O3 phases are reported in this paper, where the influence of the substrate material, the growth conditions and the variation of precursors on the phase formation is investigated.
TL;DR: This work demonstrates direct evidence of the metallic 1T phase and 3d1 electronic configuration in monolayer VTe2 that also features a (4 × 4) charge density wave order at low temperatures.
Abstract: We present a combined experimental and theoretical study of monolayer vanadium ditelluride, VTe2, grown on highly oriented pyrolytic graphite by molecular-beam epitaxy. Using various in situ microscopic and spectroscopic techniques, including scanning tunneling microscopy/spectroscopy, synchrotron X-ray and angle-resolved photoemission, and X-ray absorption, together with theoretical analysis by density functional theory calculations, we demonstrate direct evidence of the metallic 1T phase and 3d1 electronic configuration in monolayer VTe2 that also features a (4 × 4) charge density wave order at low temperatures. In contrast to previous theoretical predictions, our element-specific characterization by X-ray magnetic circular dichroism rules out a ferromagnetic order intrinsic to the monolayer. Our findings provide essential knowledge necessary for understanding this interesting yet less explored metallic monolayer in the emerging family of van der Waals magnets.
TL;DR: In this paper, a high performance MIR photodetector directly grown on silicon by molecular beam epitaxy was reported. But the authors did not specify the growth procedure of the Si platform.
Abstract: Mid-infrared (MIR) silicon photonics holds the potential for realizing next generation ultracompact spectroscopic systems for applications in gas sensing, defense, and medical diagnostics. The direct epitaxial growth of antimonide-based compound semiconductors on silicon provides a promising approach for extending the wavelength of silicon photonics to the longer infrared range. This paper reports on the fabrication of a high performance MIR photodetector directly grown onto silicon by molecular beam epitaxy. The device exhibited an extended cutoff wavelength at ∼5.5 μm and a dark current density of 1.4 × 10–2 A/cm2 under 100 mV reverse bias at 200 K. A responsivity of 0.88 A/W and a specific detectivity in the order of 1.5 × 1010 Jones was measured at 200 K under 100 mV reverse bias operation. These results were achieved through the development of an innovative structure which incorporates a type-II InAs/InAsSb superlattice-based barrier nBn photodetector grown on a GaSb-on-silicon buffer layer. The difficulties in growing GaSb directly on silicon were overcome using a novel growth procedure consisting of an efficient AlSb interfacial misfit array, a two-step growth temperature procedure and dislocation filters resulting in a low defect density, antiphase domain free GaSb epitaxial layer on silicon. This work demonstrates that complex superlattice-based MIR photodetectors can be directly integrated onto a Si platform, which provides a pathway toward the realization of new, high performance, large area focal plane arrays and mid-infrared integrated photonic circuits.
TL;DR: In this article, the selective-area chemical beam epitaxial growth of InAs in-plane, one-dimensional (1D) channels using patterned SiO2-coated InP(001), InP (111)B, and InAs(011) substrates to establish a scalable platform for topological superconductor networks was reported.
Abstract: We report on the selective-area chemical beam epitaxial growth of InAs in-plane, one-dimensional (1D) channels using patterned SiO2-coated InP(001), InP(111)B, and InP(011) substrates to establish a scalable platform for topological superconductor networks. Top-view scanning electron micrographs show excellent surface selectivity and dependence of major facet planes on the substrate orientations and ridge directions, and the ratios of the surface energies of the major facet planes were estimated. Detailed structural properties and defects in the InAs nanowires (NWs) were characterized by transmission electron microscopic analysis of cross-sections perpendicular to the NW ridge direction and along the NW ridge direction. Electrical transport properties of the InAs NWs were investigated using Hall bars, a field effect mobility device, a quantum dot, and an Aharonov-Bohm loop device, which reflect the strong spin-orbit interaction and phase-coherent transport characteristic present in the selectively grown InAs systems. This study demonstrates that selective-area chemical beam epitaxy is a scalable approach to realize semiconductor 1D channel networks with the excellent surface selectivity and this material system is suitable for quantum transport studies.
TL;DR: In this article, an 8 μm thick single-crystalline α-Ga2O3 epilayers have been heteroepitaxially grown on sapphire (0001) substrates via mist chemical vapor deposition technique.
Abstract: The 8 μm thick single-crystalline α-Ga2O3 epilayers have been heteroepitaxially grown on sapphire (0001) substrates via mist chemical vapor deposition technique. High resolution X-ray diffraction measurements show that the full-widths-at-half-maximum (FWHM) of rocking curves for the (0006) and (10-14) planes are 0.024° and 0.24°, and the corresponding densities of screw and edge dislocations are 2.24 × 106 and 1.63 × 109 cm−2, respectively, indicative of high single crystallinity. The out-of-plane and in-plane epitaxial relationships are [0001] α-Ga2O3//[0001] α-Al2O3 and [11-20] α-Ga2O3//[11-20] α-Al2O3, respectively. The lateral domain size is in micron scale and the indirect bandgap is determined as 5.03 eV by transmittance spectra. Raman measurement indicates that the lattice-mismatch induced compressive residual strain cannot be ruled out despite the large thickness of the α-Ga2O3 epilayer. The achieved high quality α-Ga2O3 may provide an alternative material platform for developing high performance power devices and solar-blind photodetectors.
TL;DR: In this article, a-SiOx was scavenged via in situ scavenging of the native aSiOx under ballistic conditions, which enabled the direct epitaxy of polar phases on Si using pulsed laser deposition.
Abstract: Ultra-thin Hf1-xZrxO2 films have attracted tremendous interest owing to their Si-compatible ferroelectricity arising from polar polymorphs. While these phases have been grown on Si as polycrystalline films, epitaxial growth was only achieved on non-Si substrates. Here we report direct epitaxy of polar phases on Si using pulsed laser deposition enabled via in situ scavenging of the native a-SiOx under ballistic conditions. On Si (111), polar rhombohedral (r)-phase and bulk monoclinic (m-) phase coexist, with the volume of the former increasing with increasing Zr concentration. R-phase is stabilized in the regions with a direct connection between the substrate and the film through the compressive strain provided by an interfacial crystalline c-SiO2 layer., The film relaxes to a bulk m-phase in regions where a-SiOx regrows. On Si (100), we observe polar orthorhombic o-phase coexisting with m-phase, stabilized by inhomogeneous strains at the intersection of monoclinic domains. This work provides fundamental insight into the conditions that lead to the preferential stabilization of r-, o- and m-phases.
TL;DR: In this article, liquid phase epitaxy (LPE) was used for the deposition of yttrium iron garnet (YIG) films with low ferromagnetic resonance losses and consistently high magnetic quality down to a thickness of 20 nm.
Abstract: The field of magnon spintronics is experiencing an increasing interest in the development of solutions for spin-wave-based data transport and processing technologies that are complementary or alternative to modern CMOS architectures. Nanometer-thin yttrium iron garnet (YIG) films have been the gold standard for insulator-based spintronics to date, but a potential process technology that can deliver perfect, homogeneous large-diameter films is still lacking. We report that liquid phase epitaxy (LPE) enables the deposition of nanometer-thin YIG films with low ferromagnetic resonance losses and consistently high magnetic quality down to a thickness of 20 nm. The obtained epitaxial films are characterized by an ideal stoichiometry and perfect film lattices, which show neither significant compositional strain nor geometric mosaicity, but sharp interfaces. Their magneto-static and dynamic behavior is similar to that of single crystalline bulk YIG. We found, that the Gilbert damping coefficient alpha is independent of the film thickness and close to 1 x 10-4, and that together with an inhomogeneous peak-to-peak linewidth broadening of delta H0|| = 0.4 G, these values are among the lowest ever reported for YIG films with a thickness smaller than 40 nm. These results suggest, that nanometer-thin LPE films can be used to fabricate nano- and micro-scaled circuits with the required quality for magnonic devices. The LPE technique is easily scalable to YIG sample diameters of several inches.
TL;DR: In this paper, high crystalline quality heteroepitaxial diamond films were successfully formed by using grid-patterned growth on Ir with dc plasma CVD, and the crystalline qualities were evaluated by X-ray diffraction, Raman spectroscopy, and etch pit method.
TL;DR: The results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature, and the proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.
Abstract: We report a MoS2/GaN heterojunction-based gas sensor by depositing MoS2 over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS2 on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS2/GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25-150 °C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS2/GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS2/GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.
TL;DR: In this article, the epitaxial layers of α-Ga2O3 with different Sn doping levels were grown by halide vapor phase epitaxy on sapphire.
Abstract: Epitaxial layers of α-Ga2O3 with different Sn doping levels were grown by halide vapor phase epitaxy on sapphire. The films had shallow donor concentrations ranging from 1017 to 4.8 × 1019 cm−3. Deep level transient spectroscopy of the lowest doped samples revealed dominant A traps with level Ec − 0.6 eV and B traps near Ec − 1.1 eV. With increasing shallow donor concentration, the density of the A traps increased, and new traps C (Ec − 0.85 eV) and D (Ec − 0.23 eV) emerged. Photocapacitance spectra showed the presence of deep traps with optical ionization energy of ∼2 and 2.7 eV and prominent persistent photocapacitance at low temperature, surviving heating to temperatures above room temperature. The diffusion length of nonequilibrium charge carriers was 0.15 µm, and microcathodoluminescence spectra showed peaks in the range 339–540 nm, but no band-edge emission.
TL;DR: Temperature and laser power dependent photoluminescence analyses verify the formation of a direct band gap material with emission in the mid-infrared region and values expected for unstrained Ge0.81Sn0.19 (e.g. band gap of 0.3 eV at room temperature).
Abstract: Highly oriented Ge0.81Sn0.19 nanowires have been synthesized by a low-temperature chemical vapor deposition growth technique. The nanostructures form by a self-seeded vapor–liquid–solid mechanism. ...
TL;DR: Wafer-scale growth of 100% AB-stacked bilayer graphene films by CVD on liquid Pt3Si/solid Pt substrates showing high quality and improved mechanical properties comparable to the mechanically exfoliated flakes is reported.
Abstract: Large-area high-quality AB-stacked bilayer graphene films are highly desired for the applications in electronics, photonics and spintronics. However, the existing growth methods can only produce discontinuous bilayer graphene with variable stacking orders because of the non-uniform surface and strong potential field of the solid substrates used. Here we report the growth of wafer-scale continuous uniform AB-stacked bilayer graphene films on a liquid Pt3Si/solid Pt substrate by chemical vapor deposition. The films show quality, mechanical and electrical properties comparable to the mechanically exfoliated samples. Growth mechanism studies show that the second layer is grown underneath the first layer by precipitation of carbon atoms from the solid Pt, and the small energy requirements for the movements of graphene nucleus on the liquid Pt3Si enables the interlayer epitaxy to form energy-favorable AB stacking. This interlayer epitaxy also allows the growth of ABA-stacked trilayer graphene and is applicable to other liquid/solid substrates. Specific stacking sequence of graphene can enable observation of unusual properties however it has been difficult to obtain this over wider areas. Here, the authors report wafer-scale growth of 100% AB-stacked bilayer graphene films by CVD on liquid Pt3Si/solid Pt substrates showing high quality and improved mechanical properties comparable to the mechanically exfoliated flakes.
TL;DR: In this paper, the in situ, direct epitaxial synthesis of (0001)-oriented PdCoO2 thin films on c-plane sapphire using ozone-assisted molecular-beam epitaxy was reported.
Abstract: We report the in situ, direct epitaxial synthesis of (0001)-oriented PdCoO2 thin films on c-plane sapphire using ozone-assisted molecular-beam epitaxy. The resulting films have smoothness, structural perfection, and electrical characteristics that rival the best in situ grown PdCoO2 thin films in the literature. Metallic conductivity is observed in PdCoO2 films as thin as ∼2.0 nm. The PdCoO2 films contain 180° in-plane rotation twins. Scanning transmission electron microscopy reveals that the growth of PdCoO2 on the (0001) surface of Al2O3 begins with the CoO2 layer.