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We report about metalorganic vapor phase epitaxy of smooth nitrogen-polar AlN templates on vicinal (0001) sapphire substrates. The influence of the V/III ratio, growth temperature, growth rate, as well as sapphire-nitridation time and temperature, were studied. With 4° offcut sapphire, step-flow growth was possible only with V/III ratios below 2. However, the optimal V/III ratio required precise adjustment, possibly dependent on reactor history and geometry. A rather narrow temperature window of less than 40 °C existed for smooth surface morphology. Reducing the temperature affected adatom mobility, eventually disrupting step-flow growth; increasing the temperature favored the formation of high-aspect-ratio defects on the epilayer. A low thermal-budget nitridation step with a short nitridation time of 15 s proved to be effective in controlling polarity without inducing excessive surface damage on the sapphire substrate. The growth rate also influenced surface morphology, with an increase in RMS roughness and step-bunching for faster growths until at growth rates above 1.4 μm/h step-flow growth could no longer occur. Finally, we developed a V/III ratio fine-tuning procedure, whereby the reactor-specific value that induces optimal growth is inferred by growth-rate variations. With this method, N-polar AlN templates with sub-nanometer RMS roughness were demonstrated for both 4° and 2° offcut sapphire substrates. [ABSTRACT FROM AUTHOR]

Achieving the formation of target open crystalline lattices from colloidal particles is of paramount importance for their potential application in photonics. Examples of such desired structures are the diamond, tetrastack, and pyrochlore lattices. Here, we demonstrate that the self-assembly of tetravalent patchy particles results in the selective formation of cubic tetrastack crystals, both in the bulk and in the systems subjected to external fields exerted by the solid substrate. It is demonstrated that the presence of an external field allows for the formation of well-defined single crystals with a low density of defects. Moreover, depending on the strength of the applied external field, the mechanism of epitaxial growth changes. For weakly attractive external fields, the crystallization occurs in a similar manner as in the bulk, since the fluid does not wet the substrate. Nonetheless, the formed crystal is considerably better ordered than the crystals formed in bulk, since the surface induces the ordering in the first layer. On the other hand, it is demonstrated that the formation of well-ordered cubic tetrastack crystals is considerably enhanced by the increase in external field strength, and the formation of the thick crystalline film occurs via a series of layering transitions. [ABSTRACT FROM AUTHOR]

Due to fascinating physical properties powered by remarkable progress in chemical vapor deposition of high-quality epilayers, diamond thin films attract great attention for fabrication of nitrogen-vacancy-based solid-state spin systems capable of operating in ambient conditions. To date, diamond heteroepitaxy via bias-enhanced nucleation is an unavoidable method for reliable wafer-scale film manufacturing. In this work, we analyze the coalescence phenomena in nitrogen doped, heteroepitaxial diamond epilayers, with a particular focus on their specific role in the annihilation of macroscopic crystal irregularities such as grain boundaries, non-oriented grains, and twinned segments. Here, we also report on the growth mechanism for the "primary" crystal orientation along with a predominant formation of two different types of boundaries highlighting the {011}-type as a main source of the crystal lattice irregularities. [ABSTRACT FROM AUTHOR]

We have grown and characterized (110)-oriented YBa2Cu3O7−x (YBCO)/PrBa2(Cu0.8Ga0.2)3O7−x (PBCGO) bilayer and YBCO/PBCGO/YBCO trilayer heterostructures, which were deposited by pulsed laser deposition technique for the nanofabrication of (110)-oriented YBCO-based superconductor (S)/insulator (I)/superconductor (S) tunneling vertical geometry Josephson junction and other superconductor electronic devices. The structural properties of these heterostructures, investigated through various x-ray diffraction techniques (profile, x-ray reflectivity, pole figure, and reciprocal mapping), showed (110)-oriented epitaxial growth with a preferred c-axis-in-plane direction for all layers of the heterostructures. The atomic force microscopy measurement on the top surface of the heterostructures showed crack-free and pinhole-free, compact surface morphology with about a few nanometer root mean square roughness over the 5 × 5 μm2 region. The electrical resistivity measurements on the (110)-direction of the heterostructures showed superconducting critical temperature (Tc) values above 77 K and a very small proximity effect due to the interfacial contact of the superconducting YBCO layers with the PBCGO insulating layer. Raman spectroscopy measurements on the heterostructures showed the softening of the Ag-type Raman modes associated with the apical oxygen O(4) and O(2)-O(3)-in-phase vibrations compared to the stand-alone (110)-oriented PBCGO due to the residual stress and additional two Raman modes at ∼600 and ∼285 cm−1 frequencies due to the disorder at the Cu–O chain site of the PBCGO. The growth process and structural, electrical transport, and Raman spectroscopy characterization of (110)-oriented YBCO/PBCGO bilayer and YBCO/PBCGO/YBCO trilayer heterostructures are discussed in detail. [ABSTRACT FROM AUTHOR]

This study explores the growth and structural characteristics of N d 2 O 3 layers on virtual germanium-rich SiGe substrates on Si(111). We focus on the emergence of the hexagonal phase depending on the stoichiometry of the virtual substrate. X-ray diffraction measurements reveal a hexagonal phase when N d 2 O 3 is grown directly on Si(111), while growth on Ge leads to a cubic oxide structure. On SiGe layers, the growth of the oxide results in a mixed phase containing hexagonal and cubic regions, regardless of the Ge content. The cubic structure grown on virtual Ge substrates exhibits strong tensile strain, while layers grown on SiGe layers show no strain. In situ growth control via electron diffraction shows a dependence of the oxide structure of the surface reconstruction of the virtual substrate. Growth on a 7 × 7 reconstruction leads to hexagonal parts on Si-based substrates, while growth on c (2 × 8) results in cubic oxide growth on Ge. Furthermore, oxide layers grown on virtual SiGe substrates form an interfacial silicate layer. The thickness of the interfacial layer is influenced by the Si content and the structure of the oxide layer enabling oxygen diffusion pathways. [ABSTRACT FROM AUTHOR]

Binary kagome compounds TmXn (T = Mn, Fe, Co; X = Sn, Ge; m:n = 3:1, 3:2, 1:1) have garnered recent interest owing to the presence of both topological band crossings and flatbands arising from the geometry of the metal-site kagome lattice. To exploit these electronic features for potential applications in spintronics, the growth of high-quality heterostructures is required. Here, we report the synthesis of Fe/FeSn and Co/FeSn bilayers on Al2O3 substrates using molecular beam epitaxy to realize heterointerfaces between elemental ferromagnetic metals and antiferromagnetic kagome metals. Structural characterization using high-resolution x-ray diffraction, reflection high-energy electron diffraction, and electron microscopy reveals that the FeSn films are flat and epitaxial. Rutherford backscattering spectroscopy was used to confirm the stoichiometric window where the FeSn phase is stabilized, while transport and magnetometry measurements were conducted to verify metallicity and magnetic ordering in the films. Exchange bias was observed, confirming the presence of antiferromagnetic order in the FeSn layers, paving the way for future studies of magnetism in kagome heterostructures and potential integration of these materials into devices. [ABSTRACT FROM AUTHOR]

The spin control possibility and its application in optoelectronic devices began an intensive research into its utilization, in particular, in the wide-gap semiconductors such as GaN doped with transition metal ions. Due to a strong p–d hybridization in Ga1−xMnxN, the Curie temperature above 300 K was already expected for x = 5%, providing that the free hole concentration necessary for the hole-mediated ferromagnetism exceeds 1020 cm−3. In this context, the development of non-equilibrium techniques enabled the engineering high-quality epitaxial layers of (Ga,Mn)N exhibiting uniform ferromagnetism at low-end cryogenic temperatures. The Tutorial is focused on the molecular beam epitaxy growth method of the Mn-enriched GaN magnetic semiconductors, summarizes the (Ga,Mn)N structural and electronic studies, and explains fundamental ferromagnetic properties, including the determination of the Mn concentration and the Curie temperature based on magnetic measurements. Most studies reveal the homogenous substitution of Mn3+ ions in the GaN matrix. Nevertheless, achieving room-temperature ferromagnetism still remains a challenge. Therefore, in the Tutorial, future research is suggested that can help obtain the homogenous ferromagnetism in (Ga,Mn)N at much elevated temperatures. [ABSTRACT FROM AUTHOR]

Epitaxial NiO and CrN thin films were deposited on a single-crystal A l 2 O 3 (1 1 ¯ 02) (r-plane sapphire) using magnetron sputtering. The two materials were intentionally deposited into two different deposition chamber designs and under different conditions (temperature, pressure, gases, and energy of sputtered particles). Despite the differences in the deposition condition and material system, both materials had the same feature with uncommon tilted epitaxial growth. Through an in-depth x-ray diffraction analysis of the NaCl (B1)-structured materials on r-plane sapphire, the full twin domain epitaxial relations were determined and can be described as (110) NaCl (B 1) ∥ (4 4 ¯ 03) A l 2 O 3 and [ 1 1 ¯ 2 ] NaCl (B 1) ∥ [ 1 ¯ 1 ¯ 20 ] A l 2 O 3 . This relationship differs from the previously observed orientation of (100) NaCl (B 1) ∥ (1 1 ¯ 02) A l 2 O 3 and [ 100 ] NaCl (B 1) ∥ [ 10 1 ¯ 0 ] A l 2 O 3 . These results are of general relevance for the growth of the extended NaCl (B1)-structured cubic material family onto a r-plane sapphire substrate where similar epitaxial growth can be expected. [ABSTRACT FROM AUTHOR]

AgCrS e 2 exhibits remarkably high ionic conduction, an inversion symmetry-breaking structural transition, and is host to complex non-colinear magnetic orders. Despite its attractive physical and chemical properties and its potential for technological applications, studies of this compound to date are focused almost exclusively on bulk samples. Here, we report the growth of AgCrS e 2 thin films via molecular beam epitaxy. Single-orientated epitaxial growth was confirmed by x-ray diffraction, while resonant photoemission spectroscopy measurements indicate a consistent electronic structure as compared to bulk single crystals. We further demonstrate significant flexibility of the grain morphology and cation stoichiometry of this compound via control of the growth parameters, paving the way for the targeted engineering of the electronic and chemical properties of AgCrS e 2 in thin-film form. [ABSTRACT FROM AUTHOR]

InN holds great promise for a wide range of applications, including broadband optical devices, high-frequency electronic devices, and serving as a substrate for highly sensitive gas detectors and efficient catalysts. Nevertheless, production of high-quality InN thin films through epitaxy has remained a significant challenge. This is primarily due to complexities arising from the low dissociation temperature and the high N2 equilibrium pressure of InN, which lead to formation of numerous nitrogen vacancies and a propensity to generate indium metal nanoparticles. Efficacy of the indium bilayer pre-deposition method for InN film growth has been established in prior studies. In this work, we introduce a specialized hydrogen insertion method to further enhance nitridation of the indium bilayer. The corresponding kinetic mechanism has been demonstrated through theoretical simulations and practical epitaxy experiments, leading to the development of an optimized hydrogen insertion process. This research represents a substantial improvement over existing InN epitaxial methods that involve control of the indium bilayer and introduces a novel mechanism for enhancing InN heteroepitaxy. [ABSTRACT FROM AUTHOR]

We have studied the epitaxial growth of Si thin films on the Cd(0001) surface using low-temperature scanning tunneling microscopy. When deposited at low temperatures (100 K), Si atoms form dendritic islands with triangular shapes, indicating the existence of anisotropic edge diffusion in the process of Si film growth. After annealing to elevated temperatures, the triangular dendritic Si islands become hexagonal compact islands. Moreover, the 2D Si islands located on two different substrate terraces exhibit different heights due to the influence of quantum-well states in Cd(0001) films. Based on high-resolution scanning tunneling microscopy images, it is observed that the first, second, and third Si layers show the pseudomorphic 1 × 1 structure. In particular, the first and second layer islands reveal the opposite triangles, indicating the hexagonal close-packed stacking of Si atoms. These results provide important information for the growth of pristine Si films on metal substrates and the understanding of Si–metal interaction. [ABSTRACT FROM AUTHOR]

Lead-free piezoelectric (K, Na)NbO3 (KNN) is considered one of the promising candidates for the replacement of Pb(ZrxTi1−x)O3. Several studies underlined the issue of K and Na volatility with increasing deposition temperatures, leading to high leakage currents in thin films, which still represents a major drawback for applications. This paper shows how epitaxial growth with concomitant preferred orientation of KNN films on niobium-doped strontium titanate (Nb:STO) depends on growth temperature and substrate strain. A preferred out-of-plane polar (001) orientation of KNN is obtained at high temperatures (>600 °C), while (100) orientation is dominant for lower ones. The (001) orientation is forced out-of-plane due to the sizeable in-plane stress derived from a negative lattice mismatch of pseudo-cubic KNN with respect to the underlying cubic (001) Nb:STO substrate. Moreover, we show that K-Na deficiency and high leakage of epitaxial KNN films deposited at high temperatures are accompanied by the appearance of a pattern of orthogonal spontaneous ferroelectric domains aligned to the [100] and [010] directions of Nb:STO. This pattern, visible in secondary electron microscopy, piezoforce response microscopy, and conductive atomic force microscopy images, is uncorrelated to the surface morphology. Supported by reciprocal space mapping by x-ray diffraction, this phenomenon is interpreted as the result of strain relaxation via ferroelectric domain formation related to K-Na deficient films displaying a sizable and increasing compressive strain when grown on Nb:SrTiO3. Our findings suggest that strain engineering strategies in thin films could be used to stabilize specific configurations of piezo- and ferroelectric domains. [ABSTRACT FROM AUTHOR]

Epitaxial growth of wurtzite AlN films on Si {111} results in 19% lattice misfit, which gives rise to a large density of threading dislocations with different recombination rates of electron–hole pairs. Here, we investigate types and distributions of threading dislocations of the MOVPE-grown 200 nm AlN/Si {111} film, whereby the dislocations are visualized using the technique of wet chemical etching. Atomic force microscopy suggests the existence of four different types of etch pits without any topological differences. Cross-sectional transmission electron microscope studies on etched samples are employed to associate the types of dislocations with the shapes of their etch pits. The recombination activity of individual dislocations was quantified by measuring the electron beam induced current and by correlative measurement of topography, secondary electron imaging, and the electron beam absorbed current. The strongest recombination activity was obtained for the m + c-type (mixed), c-type (screw), and a + c-type (mixed) threading dislocations, whereas the a-type (edge) threading dislocations were nearly recombination-inactive. [ABSTRACT FROM AUTHOR]

We investigated the chemical beam epitaxy of GaP 1 − x N x grown on nominally (001) -oriented Si substrates, as desired for the lattice-matched integration of optoelectronic devices with the standard Si technology. The growth mode and the chemical, morphological, and structural properties of samples prepared using different growth temperatures and N precursor fluxes were analyzed by several techniques. Our results show that, up to x ≈ 0.04 , it is possible to synthesize smooth and chemically homogeneous GaP 1 − x N x layers with a high structural quality. As the flux of the N precursor is increased at a given temperature to enhance N incorporation, the quality of the layers degrades upon exceeding a temperature-dependent threshold; above this threshold, the growing layer experiences a growth mode transition from 2D to 3D after reaching a critical thickness of a few nm. Following that transition, the morphology and the chemical composition become modulated along the [ 110 ] direction with a period of several tens of nm. The surface morphology is then characterized by the formation of { 113 } -faceted wires, while the N concentration is enhanced at the troughs formed in between adjacent (113) and (1 ¯ 1 ¯ 3). On the basis of this study, we conclude on the feasibility of fabricating homogeneous thick GaP 1 − x N x layers lattice matched to Si (x = 0.021) or even with N content up to x = 0.04. The possibility of exceeding a N mole fraction of 0.04 without inducing coupled morphological–compositional modulations has also been demonstrated when the layer thickness is kept below the critical value for the 2D–3D growth mode transition. [ABSTRACT FROM AUTHOR]

This study presents an approach to achieve a triaxial magnetic alignment through a linear drive type of modulated rotating magnetic field by using a permanent magnet array. This magnet array generates a modulated rotating magnetic field (MRF) without moving the sample and can produce an MRF of ∼ 0.8 T. By utilizing this magnet array, DyBa2Cu3Oy (Dy123, y ∼ 7) grains were biaxially aligned. After cutting the as-aligned sample that was magnetically aligned, we observed a location dependence of the orientation degree. We achieved the higher in-plane orientation degree of ∼ 8.5° and the c-axis orientation degree of ∼ 6.0°, respectively. The 3D simulation analysis played a key role in identifying the region where the uniformity of the MRF is within the magnet array. Compared to the epitaxial growth techniques, the use of the magnet array offers a cost-effective and versatile solution for achieving triaxial magnetic alignment. [ABSTRACT FROM AUTHOR]

The epitaxial growth of boron rich hexagonal zirconium diborides (h-ZrB2+δ) thin films on Si(111) substrates using the magnetron co-sputtering technique with elemental zirconium and boron is reported. The effect of process temperature (700–900 °C) on the compositions and epitaxy quality was investigated. The chemical composition of the films was found to have a higher boron to zirconium ratio than the ideal stoichiometric AlB2-type ZrB2 and was observed to be sensitive to process temperature. Films deposited at 700 °C exhibited intense diffraction peaks along the growth direction corresponding to (000ℓ) of h-ZrB2 using both lab and synchrotron-based x-ray diffractograms. The thermal and compositional stability of the epitaxial h-ZrB2+δ film was further evaluated under a nitrogen-rich environment through isothermal annealing which showed a reduction in in-plane misorientation during thermal annealing. The relative stability of deviating compositions and the energetics of impurity incorporations were analyzed using density functional theory simulations, and the formation of native point defects or impurity incorporation in h-ZrB2 was found to be endothermic processes. Our experimental results showed that an epitaxial thin film of h-ZrB2+δ can be grown on Si(111) substrate using a magnetron co-sputtering technique at a relatively low processing temperature (700 °C) and has the potential to be used as a template for III-nitride growth on Si substrates. [ABSTRACT FROM AUTHOR]

Epitaxial VNi2 layers are deposited onto MgO(001) and their resistivity ρ measured as a function of layer thickness d = 10.5–138 nm to quantify the resistivity size effect. The layers exhibit resistivity minima at both stoichiometric V:Ni = 1:2 composition and 700 °C growth temperature, which is attributed to electron scattering at V–Ni antisite defects and is described using the ordering parameter within the framework by Rossiter. A cube-on-cube epitaxy of the fcc parent structure on MgO(001) leads to two possible layer orientations for orthorhombic VNi2(010) and VNi2(103), resulting in considerable atomic disorder at domain boundaries, consistent with relatively small x-ray coherence lengths of 8 and 14 nm in-plane and along the growth direction of a 33.5 nm thick layer. In situ ρ vs d measurements yield a bulk resistivity of ρo = 46 ± 2 μ Ω cm and a benchmark quantity of ρoλ = (138 ± 5) × 10−16 Ω m2, where λ is the bulk electron mean free path. Air exposure causes a minor resistivity increase due to 2 ± 1 nm thick surface oxide that perturbs the surface potential. Resistivities at 77 K are Δρ = 16 ± 3 μ Ω cm below those at room temperature. This Δρ is thickness independent and is close to the previously predicted 13.9 μ Ω cm bulk resistivity for VNi2 along [100]. However, the measured bulk resistivity is well above this prediction, which is attributed to electron scattering at domain boundaries/atomic disorder. Consequently, the theoretically predicted superior directional conduction cannot be experimentally confirmed in this study. The overall results indicate that VNi2 is only a promising compound for narrow interconnects if a synthesis scheme can be developed that results in a strong atomic order, a negligible domain boundary density, and a [100] crystalline orientation along the transport direction. [ABSTRACT FROM AUTHOR]

We report on a thermodynamic analysis of oxide vapor phase epitaxy (OVPE) of GaN. We first calculate equilibrium partial pressures of gases for the initial partial pressures of Ga2O, NH3, and H2 as well as the growth temperature. To estimate the growth rate of a GaN crystal, we then define the supersaturation amount determined by the equilibrium and initial partial pressures. In the calculation, the growth rate is significantly influenced by the initial partial pressures of Ga2O and NH3, while it is almost independent of the initial partial pressure of H2 and the growth temperature. Subsequently, we experimentally grow GaN crystals under same conditions as in the thermodynamic analysis. In the range of conditions in this work, the experimental growth rates are nearly consistent with the growth rates predicted by the thermodynamic analysis for all experimental parameters. Thus, the results showed that a high value of the supersaturation amount is advantageous for high-speed growth. Furthermore, we define the supersaturation ratio and investigate the correlation between this parameter and the surface coverage of the polycrystal. The surface coverage of the polycrystal is confirmed to roughly decrease as the value of the supersaturation ratio decreases. Thus, the results showed that a low value of the supersaturation ratio is advantageous for polycrystal-free growth. Finally, we use the thermodynamic analysis to explore the optimal conditions for high-speed and polycrystal-free growth. This revealed that the optimal OVPE growth conditions are both a high partial pressure of Ga2O and a low partial pressure of NH3. [ABSTRACT FROM AUTHOR]

The topological antiferromagnet γ -FeMn is a fascinating material for studying unconventional magnetic properties and topological transport phenomena though high-quality γ -FeMn has been obtained on the Cu substrate for magnetic research. However, the difficulty of growing single-crystalline γ -FeMn films on insulating substrates has prevented experiments from exactly verifying many theoretical predictions on their transport properties. Ultrathin Cu buffer films have been considered for solving this problem but failed because the crystal quality and thickness of Cu films achieved in previous works do not satisfy the growth buffer criteria for γ -FeMn. In this work, the growth of 5-nm-thick Cu films on SrTiO 3 (001) substrates was studied. It was found that single-crystalline ultrathin Cu films with roughness as low as 1 nm are obtained on the insulating substrate. We subsequently obtained high crystalline quality γ -FeMn films with smooth surface and verified their antiferromagnetism. Finally, two aspects of the influence of Cu films on adjacent films have been analyzed. Our results facilitate the experimental exploration of the fascinating properties of γ -FeMn. [ABSTRACT FROM AUTHOR]

The increasing demand for More than Moore devices requires epitaxy technology to keep up with the discovery and deployment of new semiconductors. An emerging technology for cost-effective, device-quality growth is magnetron sputter epitaxy, though detailed studies on the process itself remain scarce. Here, we report an extensive study on the correlation between the substrate off-cut and film quality in AlN-on-Si heteroepitaxy. Controlled reactive pulsed magnetron sputtering is used to grow epitaxial AlN(0001) films on in situ Ar plasma etched off-cut Si(111) substrates with growth rates above 1.5 nm/s. Substrate off-cut angles in the range of 0.02°–0.30° are investigated and precisely determined by high-resolution x-ray diffraction. Structural examination of the AlN films is carried out by transmission electron microscopy and high-resolution x-ray diffraction. The AlN/Si interface is well-defined and two types of AlN domains with epitaxial relationships are observed. The formation of secondary rotation domains deteriorates the crystal quality substantially. Substrates with small off-cuts, ideally no off-cut substrates, appear to be crucial for suppressing the formation of secondary domains and further result in a better overall crystal quality of AlN films. We discuss this effect in relation to the AlN/Si interface, the substrate pre-treatment, and nucleation. [ABSTRACT FROM AUTHOR]

Heterogeneous integration of functional oxides with ultra-wide bandgap (UWBG) semiconductors is desired for the realization of novel hybrid systems applicable to a wide array of commercial electronics and defense applications. In this work, we demonstrate the growth of crystalline SrTiO3 (STO) thin films on high-electron-mobility transistor (HEMT) heterostructures based on an emergent UWBG semiconductor ScAlN, used as the barrier layer on a GaN channel, and determine the effects of the pre-growth chemical treatments of the ScAlN surface on resultant heterostructure properties. We investigate wet chemical cleans of ScAlN with solvents, piranha solution, UV ozone and hydrofluoric acid, and a sulfuric-phosphoric acid mix prior to STO growth, and show that the commonly used piranha solution degrades the ScAlN surface, thereby reducing the crystal quality of the deposited STO layers and lowering the channel mobility. We determine that among the treatments studied, the solvent and sulfuric-phosphoric acid cleans were the least disruptive to the electrical properties of the GaN channel as evidenced from Hall effect measurements, but the sulfuric-phosphoric acid clean results in best oxide crystallinity, as determined from structural characterizations. We perform transmission electron microscopy imaging on the piranha-treated and sulfuric-phosphoric-treated samples to compare the microstructure and find that while intermixing occurs at the oxide-nitride interfaces for both samples, the interface roughness is lower and the STO grain size is larger in the sample with sulfuric-phosphoric acid treatment. This work demonstrates the first epitaxial growth of STO on an UWBG semiconductor and motivates STO/ScAlN/GaN as material platforms for high-frequency, high-power-density HEMTs. [ABSTRACT FROM AUTHOR]

GaSb grown on GaAs through interfacial misfit (IMF) arrays grown via molecular beam epitaxy has been heavily studied; there is limited research, however, on IMF growth through metal-organic vapor phase epitaxy. To demonstrate viability for integration in a multijunction solar cell for terrestrial use, it is imperative to demonstrate high quality GaSb grown on GaAs through metal-organic vapor phase epitaxy. The preferred gallium precursors for n-type and p-type GaSb for longest minority carrier diffusion length were determined to be trimethylgallium and triethylgallium, respectively. A heteroepitaxial GaSb-on-GaAs device attained an open-circuit voltage of 190 mV and an efficiency of 2.2%. Extracted threading dislocation density from the minority carrier lifetime for the heteroepitaxial GaSb-on-GaAs device was determined to be 7.5 × 10 6 cm − 2 . In a modeled multijunction solar cell, this device attributes to an overall efficiency of 33.1% under AM1.5g illumination. [ABSTRACT FROM AUTHOR]

Over the last few decades, research thrust in the growth and engineering of high quality atomically smooth epitaxial thin films have increased tremendously, displaying unprecedented quantum correlated phenomena and ample potential for oxitronics. Regardless of the significant progress made thus far, the growth of high quality defect-free atomically smooth epitaxial conducting perovskite oxide thin films continues to be a very active area of research, as several intrinsic and/or extrinsic factors affect the film quality and consequent electronic properties. Here, we made efforts to summarize the progress made with focus on the growth of atomically smooth electronic quality epitaxial thin films of several highly conducting ABO3 perovskites with low resistivity (high conductivity). Concomitantly, optimization of growth parameters (kinetics and thermodynamics of the material) and the film–substrate interaction seems to play a crucial role in epitaxy quality. Highly conducting epitaxial oxide thin films are pivotal in bridging the gap between oxides and the practicalities in integrating them for electronics. [ABSTRACT FROM AUTHOR]

High-temperature annealing (HTA) is one of the most promising techniques to produce high-quality, cost-efficient AlN templates for further epitaxial growth of AlGaN devices. Unfortunately, the yield of this process seems to be limited due to the restricting face-to-face configuration that is typically used, in which contaminations of the template surface can occur easily. A high yield is crucial for process transfer into industry. Indeed, templates that are annealed in open-face configuration suffer from surface degradation due to excessive AlN evaporation during the course of the annealing process. To highlight the physics that are restricting the open-face approach of the process, sublimation behavior of AlN at temperatures and atmospheres typically used in HTA processes has to be examined. In this study, we use the Knudsen effusion mass spectrometry technique to confirm the previously published results on equilibrium partial pressures of species above AlN. Based on the experimentally determined data and further AlN sublimation experiments, the apparent sublimation coefficient of AlN in N2 and Ar atmospheres at HTA process conditions can be derived. Despite N2 having a stabilizing effect on AlN during HTA, the still high decomposition rates of several hundred nanometers per hour can explain the excessive damage that is typically observed if AlN/sapphire templates are annealed in an open-face configuration. Finally, based on theoretical considerations, a strategy to reduce the sublimation of AlN during HTA in open-face configuration is suggested. [ABSTRACT FROM AUTHOR]

The incorporation of quantum dots in display technology has fueled a renewed interest in InP-based quantum dots, but difficulty controlling the Zn chemistry during shelling has stymied thick, even ZnSe shell growth. The characteristic uneven, lobed morphology of Zn-based shells is difficult to assess qualitatively and measure through traditional methods. Here, we present a methodological study utilizing quantitative morphological analysis of InP/ZnSe quantum dots to analyze the impact of key shelling parameters on InP core passivation and shell epitaxy. We compare conventional hand-drawn measurements with an open-source semi-automated protocol to showcase the improved precision and speed of this method. Additionally, we find that quantitative morphological assessment can discern morphological trends in morphologies that qualitative methods cannot. In conjunction with ensemble fluorescence measurements, we find that changes to shelling parameters that promote even shell growth often do so at the cost of core homogeneity. These results indicate that the chemistry of passivating the core and promoting shell growth must be balanced carefully to maximize brightness while maintaining emission color-purity. [ABSTRACT FROM AUTHOR]

It is highly challenging to grow high-quality gallium nitride (GaN) layers on silicon (Si) substrates due to the intrinsic mismatching of their structural and thermal properties. Aluminum nitride (AlN) interlayers have been used to induce a compressive strain to GaN layers during growth, which compensates for the tensile strain in these layers on Si substrates during cooling. In this study, we investigated the effect of the growth temperature and layer structure of the AlN interlayer to understand the relationship between surface flatness and relaxation ratio of the AlN interlayer and the compressive strain in the overlying GaN layer. Low-temperature (LT) growth enhanced lattice relaxation of the AlN interlayer, whereas the AlN surface was atomically flat at high temperature (HT). We also examined a two-step growth to combine the advantages of LT- and HT-AlN. This approach resulted in a surface with multiple flat regions separated by grooves, which had the largest compressive strain in the overlying GaN layer at the early stages of growth. At later stages, the strain was the largest on the HT-AlN interlayer. In both cases, the experimentally measured compressive strain exceeded simulated predictions. Finally, possible solutions for inducing a larger compressive strain in the GaN layer using interlayers were discussed. [ABSTRACT FROM AUTHOR]

High-quality and low-defect-density germanium (Ge) buffer layers on silicon (Si) substrates have long been developed for group IV and III–V devices by suppressing defect propagation during epitaxial growth. This is a crucial step for the development of highly efficient photonic devices on Si substrates. Patterned silicon substrates have increasingly been employed for their ability to restrict and hinder the motion of defects. In this work, we demonstrate the effectiveness of an optimised two-step growth recipe structure on a (111)-faceted V-groove silicon substrate with a 350 nm flat ridge. This strategy successfully reduces the threading dislocation (TD) density while growing a 1 μ m Ge buffer layer via molecular beam epitaxy. As a result, a high-quality buffer is produced with a low TD density on the order of 107 cm−2 and a surface roughness below 1 nm. [ABSTRACT FROM AUTHOR]

α-Al 2 O 3 as a preferred material for hydrogen isotopes permeation barrier (HIPB) can effectively prevent hydrogen embrittlement in structural steel and has higher thermal stability. However, its application is limited by the issue that it is hard to prepare α-Al 2 O 3 at relatively low temperature and its formation temperature is too high (>1000 °C) to damage the mechanical properties of structural steel. To overcome this issue, this paper presents a novel method (combining Al electrodeposition, aluminizing, Cr deposition and air oxidation) for the preparation of α-Al 2 O 3 (Cr 2 O 3)/Fe–Al composite coating on 316 L stainless steel for the first time. The formation temperature of α-Al 2 O 3 was successfully reduced to 800 °C. The post-oxidation samples were characterized by SEM, XPS, XRD, EDS and TEM. The results showed that the oxide film was composed of highly crystalline α-Al 2 O 3 and Cr 2 O 3 nanoparticles, where the later were diffusely distributed in the internal α-Al 2 O 3 film. And there was an epitaxial growth relationship between α-Al 2 O 3 and Cr 2 O 3. The low-temperature formation of the α-Al 2 O 3 film was due to the fact that the Cr 2 O 3 nanoparticles formed during the oxidation process acted as templates and nucleation sites, which reduced the nucleation barrier of α-Al 2 O 3. Deuterium permeation tests showed that its deuterium permeation reduction factor (DPRF) was 8892 at 500 °C, which met the standard for practical application. [ABSTRACT FROM AUTHOR]

BaTiO3(BT)‐templated 0.5Pb(Ni1/3Nb2/3)O3–0.16PbZrO3–0.34PbTiO3 with 0.2 wt% Li2CO3 (PNN‐PZT + LC) ceramics were successfully sintered at temperatures less than 1050°C. Their structural, ferroelectric, and piezoelectric properties were systematically investigated as a function of amount of BT, which ranged from 2 to 10 vol%. The PNN‐PZT + LC ceramics sintered at 1000°C showed highly textured morphologies with preferred (0 0 1) orientation, having Lotgering factors (fL) of 85% and higher. When sintering temperature exceeded 1000°C, the epitaxial grain growth of PNN‐PZT + LC rhombohedral phase, driven by BT templates, was hindered by dramatically enlarged matrix grains. In situ X‐ray diffractometry analyses are performed to identify phase transition behavior depending on temperature. Properties of d33 (1180 pC/N) and kp (80.3%) were obtained for the 2 vol% BT‐templated PNN‐PZT + LC ceramic sintered at 1000°C, along with ferroelectric properties of 2Pr (56.1 μC/cm2) and 2Ec (1.26 kV/mm) at 3.5 kV/mm. High‐resolution transmission electron microscopy and piezo‐response force microscopy were utilized to investigate domain structure and epitaxial grain growth between templated BaTiO3 and matrix ceramics. The low‐temperature sintered specimen showed an extremely large electrostrain characteristic (d33*) of 1215 pm/V at 1 kV/mm. Furthermore, textured multilayer piezoelectric actuators exhibited higher actuator performance and lower energy loss compared to untextured multilayer piezoelectric actuators, indicating their potential for use in piezoelectric actuator devices. [ABSTRACT FROM AUTHOR]

Pb[Zr,Ti]O 3 (PZT) thin films with the Zr/Ti ratio of 45/55, 52/48, and 60/40 (PZT(45/55), PZT(52/48), and PZT(60/40), respectively) are deposited on (001)SrRuO 3 /(001)Pt/ZrO 2 /Si by sol-gel method. We confirm that the epitaxial (001)Pt electrode facilitate the epitaxial growth of the PZT thin films along the c -axis direction. Basic characteristics such as structural, dielectric, and ferroelectric properties are examined. Furthermore, direct and converse piezoelectric properties are evaluated using effective transverse piezoelectric coefficients, | e 31, f |. In particular, the epitaxial PZT thin films manifest a dependence of the converse | e 31, f | on applied voltages with the values as follows; 9.7–11.5 C/m2, 11.2–12.5 C/m2, and 11.7–12.3 C/m2 for the epitaxial PZT(45/55), PZT(52/48), and PZT(60/40), respectively. Moreover, by analyzing bias-resolved in-situ reciprocal space map (RSM) obtained from synchrotron radiation X-ray diffraction (SR-XRD) which allows for the understanding on the transition of crystal structures, we explore the voltage-induced contributions for the converse | e 31, f |. [ABSTRACT FROM AUTHOR]

The mechanical properties of zinc anodes in rechargeable zinc‐based batteries are neglected. Indeed, electrode stress in zinc crystallization (ESZC) contributes to excess chemical potential under enormous deposition stress, severely impacting zinc crystal patterns and reaction kinetics. Herein, a stress prerelease mechanism to minimize ESZC and drive dendrite‐free zinc anode growth is proposed. The internal stress of the freestanding electrode is prereleased by full‐contact soft‐substrate constraints during fabrication. Under the compression of crystallization stress, the freestanding electrode rapidly deforms and self‐releases into microstrains to reduce ESZC. Furthermore, the weakening of ESZC under the stress‐prerelease mechanism is modified to the actual reaction kinetics, which establishes a direct link between electrode stress and zinc deposition pattern. The processes of crystalline stress transfer and self‐release under the stress prerelease mechanism are revealed using in situ strain monitors. Stress‐prereleased freestanding electrodes drive uniform zinc nucleation and subsequent radial diffusion, guiding Zn epitaxial growth on the nanofibers surface. During repeated deposition/stripping, the stress prerelease mechanism steadily diminishes the possibility of dendrite growth and guarantees the stable operation of dendrite‐free zinc anodes. The stress prereleased freestanding electrodes induce symmetric and full cells to achieve stable and excellent performance. [ABSTRACT FROM AUTHOR]

Many properties of the emerging class of metal‐organic frameworks (MOFs) depend crucially on defect concentrations, as in case of other solids. In order to provide reference systems with nearly perfect structure and low defect density, a procedure to grow MOFs epitaxially on cm‐sized Si(111) single crystals is developed. The crystalline metal‐organic thin films are in high registry with the substrate's crystal lattice, as demonstrated by synchrotron‐based grazing incidence X‐ray diffraction (GI‐XRD) experiments. The corresponding reduction of MOF defect density is shown to have striking effects on the properties of these porous frameworks. The most pronounced difference concerns mass transport. An increase in the diffusion coefficient of guest molecules by one order of magnitude relative to the same MOF materials with normal defect densities is observed. [ABSTRACT FROM AUTHOR]

Co-condensation of mixed SiGe nanoclusters and impingement of SiGe nanoclusters on a Si substrate were applied using molecular dynamics (MD) simulation in this study to mimic the fast epitaxial growth of SiGe/Si heterostructures under mesoplasma chemical vapor deposition (CVD) conditions. The condensation dynamics and properties of the SiGe nanoclusters during the simulations were investigated first, and then the impingement of transient SiGe nanoclusters on both Si smooth and trench substrate surfaces under varying conditions was studied theoretically. The results show that the mixed nanoclusters as precursors demonstrate potential for enhancing epitaxial SiGe film growth at a high growth rate, owing to their loosely bound atomic structures and high mobility on the substrate surface. By varying cluster sizes and substrate temperatures, this study also reveals that smaller clusters and higher substrate temperatures contribute to faster structural ordering and smoother surface morphologies. Furthermore, the formed layers display a consistent SiGe composition, closely aligning with nominal values, and the cluster-assisted deposition method achieves the epitaxial bridging of heterostructures during cluster impingement, highlighting its additional distinctive characteristics. The implications of this work make it clear that the mechanism of fast alloyed epitaxial film growth by cluster-assisted mesoplasma CVD is critical for extending it as a versatile platform for synthesizing various epitaxial films. [ABSTRACT FROM AUTHOR]

Defect-free thin-walled samples were built using wire arc additive manufacturing (WAAM) combined with the "coldArc" deposition technique by feeding a Ti-6Al-4V welding wire and using two deposition strategies, namely with and without the welding torch weaving. The microstructures formed in these samples were examined in relation to mechanical characteristics. The arc torch weaving at 1 Hz allowed us to interfere with the epitaxial growth of the β-Ti columnar grains and, thus, obtain them a lower aspect ratio. Upon cooling, the α/α′+β structure was formed inside the former β-Ti grains, and this structure proved to be more uniform as compared to that of the samples built without the weaving. The subtransus quenching of the samples in water did not have any effect on the structure and properties of samples built with the arc torch weaving, whereas a more uniform grain structure was formed in the sample built without weaving. Quenching resulted also in a reduction in the relative elongation by 30% in both cases. [ABSTRACT FROM AUTHOR]

The chemical vapor deposition of silicon on a patterned silicon substrate leads to the formation of 3D microcrystals, which, due to their inclined top facets and high aspect ratio, produce a light‐trapping effect enhancing the optical absorption in the near‐infrared (NIR). In this work, it is demonstrated that Si microcrystals can form the building blocks of a new class of NIR sensitive photodetectors operating in a linear or avalanche regime. Microcrystal‐based devices are designed by coupling a 2D kinetic‐growth model with a Poisson drift‐diffusion solver and fabricated by combining electron beam lithography and low‐energy plasma‐enhanced chemical vapor deposition (LEPECVD). The optoelectronic properties of microcrystal‐based p–i–n photodiodes are investigated both theoretically and experimentally by means of finite‐difference time‐domain (FDTD) simulations and responsivity measurements. At 1000 nm wavelength, the responsivity of microcrystal‐based devices is six times higher than that of an equivalent mesa diode. Moreover, the photocurrent gains of Si microcrystals operating as an avalanche photodiode (APD), at the same wavelength, reaches 2 × 104 demonstrating the potentialities of substrate patterning, combined with epitaxial growth, for amplified photodetection applications. [ABSTRACT FROM AUTHOR]

This paper is concerned with the well-posedness and asymptotic behavior for a singular epitaxial thin-film growth equation with logarithmic nonlinearity under the Navier boundary condition. Based on the technique of cut-off and combining with Hardy-Sobolev inequality, the technique of Faedo-Galerkin, and multiplier, we establish the local solvability. Meantime, by virtue of the family of potential wells, we obtain the threshold between the existence and nonexistence of the global solution (including the critical case) and give the upper bound of lifespan and the estimate of blow-up rate. Furthermore, the results of blow-up with arbitrary initial energy and the lifespan are derived. [ABSTRACT FROM AUTHOR]

Traditional chemical solution deposition (CSD) methods for growing Ga2O3 films face two main issues: limited thickness per deposition, necessitating multiple coating-annealing cycles for adequate film thickness, and a decline in crystal quality with increased thickness. This study introduces an innovative CSD technique for fabricating (GaAl)2O3 films, achieving both high thickness and superior crystal quality, where the aluminum content results from the diffusion of aluminum from sapphire substrates during annealing. The technique uses a precursor solution with high viscosity and cation concentration, allowing single-layer thicknesses of up to 180 nm. Additionally, the incorporation of silver nitrate for silver doping enhances nucleation, growth, and epitaxial quality, inducing a unique twelve-fold symmetry in the (−201) oriented (GaAl)2O3 films. Notably, silver serves as a catalyst and largely evaporates at high temperatures, thus preserving the film's final composition and performance. This study highlights the effectiveness of this CSD approach in simultaneously improving crystal quality and achieving desired film thickness, making it a promising method for mass production of high-quality (GaAl)2O3 films. [ABSTRACT FROM AUTHOR]

In this paper we examine well-posedness for a class of fourth-order nonlinear parabolic equation ∂ t u + (− Δ) 2 u = ∇ ⋅ F (∇ u) , where F satisfies a cubic growth conditions. We establish existence and uniqueness of the solution for small initial data in local BMO spaces. In the cubic case F (ξ) = ± | ξ | 2 ξ , we also examine the large time behaviour and stability of global solutions for arbitrary and small initial data in VMO, respectively. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) van der Waals heterostructures (vdWHs) received intensive interest due to their amazing physical properties and broad applications in fields such as ultrasensitive sensors, transistors, and solar cells. Although remarkable progresses were achieved for the synthesis of 2D vdWHs, great challenges still remain for the easy preparation of 2D vdWHs because of the weak interlayer coupling. As a type of 2D semiconductor, the 2D SnSe film is particularly appealing for optoelectronic and thermoelectric devices because of its high thermoelectric and optoelectronic performance. However, the easy preparation of large-area and high-quality 2D SnSe films remains a great challenge. In this work, we proposed an approach to regulate the preparation of high-quality 2D vdWHs, which employed the polarization field of substrate as a key factor to control the diffusion barriers of the adsorbed Sn and Se atoms. Hexagonally stacking α-In2Se3 was selected as such polarized substrate because this substrate exhibits out-of-plane ferroelectricity with upward or downward polarized states at room temperature, and the two degenerated polarized states can be easily switched by applying an external electric field. It was revealed that the polarization field of α-In2Se3 can substantially influence the diffusion behavior of Sn and Se atoms on polarized α-In2Se3 substrate. So, the film growth property of SnSe film is sensitive to the polarization direction of In2Se3 substrate. Our research provides an ideal method to explore the possibility of building 2D functional nanoelectronic devices. [ABSTRACT FROM AUTHOR]

Trench epitaxy of 4H-SiC is investigated with the supersaturation of chlorinated chemistry at a growth temperature of 1550 °C. Coupled with a lower growth temperature than has been previously reported, the integrity of the 4H-SiC trenches is retained and minimal rounding effects of H2 annealing prior to growth are observed. The system gives different growth rates of materials on the various crystal faces of the trenches and can be used to improve the refilling process, resulting in the reduced void formation. The addition of excessive levels of HCl can suppress trench epitaxy by reducing the growth rate on the sidewalls of trenches in favor of growth on the surface. The processes demonstrated offer a scalable and reproducible method to fabricate SiC-based superjunction device structures for applications in high voltage power electronics. [ABSTRACT FROM AUTHOR]

We demonstrate the selective area growth of InGaAs nanowires (NWs) on GaAs (111)B substrates using hydride vapor phase epitaxy (HVPE). A high growth rate of more than 50 μ m h−1 and high aspect ratio NWs were obtained. Composition along the NWs was investigated by energy dispersive x-ray spectroscopy giving an average indium composition of 84%. This is consistent with the composition of 78% estimated from the photoluminescence spectrum of the NWs. Crystal structure analysis of the NWs by transmission electron microscopy indicated random stacking faults related to zinc-blende/wurtzite polytypism. This work demonstrates the ability of HVPE for growing high aspect ratio InGaAs NW arrays. [ABSTRACT FROM AUTHOR]

This study reports the pulsed sputtering deposition (PSD) epitaxial growth of In–Mg‐codoped GaN with a high hole concentration of 6.2 × 1018 cm−3 and its hole conduction mechanism. X‐ray diffraction analysis shows that In–Mg‐codoped GaN coherently grows on a GaN substrate without structural degradation and In concentration is 1.3%. Temperature‐dependent conductivity is explained by the combination of the band and nearest‐neighbor hopping conduction models. Curve fitting in the band conduction region is used to estimate the Mg activation energy, which is as low as 89 meV. This is responsible for the high hole concentration of 6.2 × 1018 cm−3. These results indicate that In–Mg codoping using low‐temperature PSD is a promising technique for the preparation of GaN with a high hole concentration without structural degradation. [ABSTRACT FROM AUTHOR]

The article presents the study on the comparison of gain coefficient of laser diode on silicon and InP substrate. Fabry–Perot GaInAsP bulk laser diode on InP/Si substrate is successfully obtained to study the optical gain coefficient of laser diode. The influences of temperature, threshold current comparison, and optical gain achievements between bulk InP/Si laser diode substrate and InP laser diode substrate are also analyzed using the same growth structure. A new approach is found by the research group which involves bonding of 1 μm InP semiconductor crystal and a low‐cost silicon crystal prior to epitaxial laser structure growth. With the help of metal–organic vapor‐phase epitaxy technique, GaInAsP double‐heterostructure laser is epitaxially deposited on the well‐bonded InP/Si crystal. Fabry–Perot lasing under pulsed condition is achieved, and the lasing characteristics of InP/Si substrate are compared with that of InP laser device to study the gain coefficient. [ABSTRACT FROM AUTHOR]

The liquid-phase epitaxial growth (LPE) of GaN crystals on the MOCVD-GaN substrate using the Na-flux method was investigated under various growth times, 30, 60, 100, and 150 h. The morphology properties of as-grown GaN crystals were characterized by the scanning electron microscope (SEM). The variation of nitrogen concentration and supersaturation of GaN in the Ga-Na melt as a function of time is given computationally during the growth time of 150 h, as well as the distribution of nitrogen concentration for 30, 60, 100, and 150 h. In the early term of LPE growth (Stage I), the growth proceeds in a near-equilibrium laminar pattern at lower growth driving forces, corresponding to a screw dislocation growth mechanism. As the growth time extends, the GaN supersaturation in the Ga-Na melt increases with mass transfer continuing, leading to the mechanism of LPE growth changing from screw dislocation growth to continuous hexagonal pyramidal growth with deeper and deeper pit depths, and also thereby leading to the emergence of Stage II. A high level of GaN supersaturation in the solution could promote the growth along the vertical direction of Stage II but is detrimental to the layer growth of Stage I. Broadening the growth of Stage I could realize near-equilibrium growth of GaN crystals and improve the crystalline quality of epitaxial GaN crystals. The specific mechanisms of the different stages of GaN crystal growth were not clarified in the previous work. Through a combination of experimental and simulation calculations, the GaN crystal growth mechanism was discussed. Based on the growth mechanism acquired, the growth process may be effectively regulated to obtain high-quality GaN single crystals. [ABSTRACT FROM AUTHOR]

[Display omitted] • PBA@CCH nanocubes are successfully constructed via an in-situ epitaxial growth strategy. • The morphology and structure of the coating can be modulated by varying the composition of reaction reagents. • The formation mechanism of the coating with variable morphology are discussed and analyzed in detail. • The CoNi2S4/Co9S8@Co4S3 heterogeneous nanocubes are fabricated via one-step carbonization and sulfidation method. Construction of Prussian blue analogues (PBAs) with heterostructure is beneficial to preparing PBAs derivatives with superior electrochemical performance. In this work, the core–shell nanostructured nanocubes composed of nickel hexacyanocobalt PBA (NiCo-PBA)@cobalt carbonate hydroxide (CCH) are synthesized through an in-situ epitaxial growth strategy, and the formation mechanisms of coating are carefully validated and specifically discussed. Then, the precursors are successfully transformed into hierarchical CoNi 2 S 4 /Co 9 S 8 @Co 4 S 3 via the gas-phase vulcanization method. Benefiting from the intriguing heterostructure and multicomponent sulfides, the CoNi 2 S 4 /Co 9 S 8 @Co 4 S 3 -80 electrode exhibits a high specific capacity of 799 ± 16C/g (specific capacitance of 1595 ± 31F/g) at 1 A/g, ultra-high capacity retention of 80 % at a high current density of 20 A/g. The assembled asymmetric supercapacitor (ASC) device delivers a high energy density of 43.3 Wh kg−1 at a power density of 899 W kg−1 and exhibits superior cycling stability with the capacity retention of 88 % after 5,000 cycles. Subsequently, the fabricated all-solid-state ASC device shows an excellent energy density of 36.4 Wh kg−1 with a power density of 824 W kg−1. This work proposing rational design of combining multicomponent sulfides and core–shell heterostructure based on PBA nanocubes opens up a novel route for developing asymmetric supercapacitor electrode materials with superior performance. [ABSTRACT FROM AUTHOR]

In this work, we present a stress-free AlN film with improved crystal quality assisted by h-BN and demonstrate the mechanical exfoliation of wafer-scale single-crystal AlN freestanding membrane and reveal the controllable exfoliation mechanism of AlN. Uniform and continuous wafer-scale h-BN is directly grown on c-plane sapphire using a flow modulation epitaxy mode by metal-organic chemical vapor deposition. The nucleation and evolution processes of quasi-van der Waals epitaxy (QvdWE) of AlN on h-BN are revealed. It is found that O2-plasma-treated h-BN can effectively promote the nucleation islands of AlN and contribute to the release of biaxial stress and the reduction of dislocation density in the epilayers. Eventually, the QvdWE growth of a stress-free AlN film (0.08 GPa) is achieved, and wafer-scale mechanical exfoliation of the AlN membrane has been realized. This work provides an effective strategy for the quality improvement of III-nitride films and paves the way for the vertical structure and flexible deep-ultraviolet optoelectronic devices. [ABSTRACT FROM AUTHOR]

The large polarization barriers between the quantum wells and quantum barriers in long-wavelength GaN-based light-emitting diodes (LEDs) inhibit their performance by requiring excess driving voltages to reach standard operating current densities. Lateral injection of carriers directly into quantum wells is required to circumvent this issue. V-defects are naturally occurring inverted hexagonal defects with semipolar 10 1 ¯ 1 -plane sidewalls generated on surface depressions from threading dislocations. LEDs engineered to intentionally generate V-defects below the active region of the LED can achieve lateral carrier injection through the V-defect sidewalls and have already been able to demonstrate world record wall-plug efficiencies for LEDs in the green-red wavelengths. V-defects can be enlarged during kinetically limited growth where the growth rate of the c-plane GaN is faster than that of their sidewalls, leaving them unfilled. We report on the metal organic chemical vapor deposition growth conditions required to fill in V-defects with p-GaN during epitaxial growth of the LED post the active region. Circular transmission length measurements of Pd/Au contacts processed on p-GaN surfaces with various amounts of unfilled V-defects showed no significant difference in their sheet resistance and specific contact resistance. J–V measurements of LEDs grown with varying unfilled V-defect densities showed no significant difference in the forward bias regime. However, in the reverse bias regime, catastrophic breakdown occurred at markedly lower voltages for samples with larger unfilled V-defect densities. This suggests that unfilled V-defects may act as hotspots for device failure, and planarizing LED surfaces may help prevent early degradation of LED devices. [ABSTRACT FROM AUTHOR]

Development of bulk acoustic wave filters with ultra-wide pass bands and operating at high frequencies for 5th and 6th generation telecommunication applications and micro-scale actuators, energy harvesters and sensors requires lead-free piezoelectric thin films with high electromechanical coupling and compatible with Si technology. In this paper, the epitaxial growth of 36°Y-X and 30°X-Y LiNbO3 films by direct liquid injection chemical vapour deposition on Si substrates by using epitaxial SrTiO3 layers, grown by molecular beam epitaxy, has been demonstrated. The stability of the interfaces and chemical interactions between SrTiO3, LiNbO3 and Si were studied experimentally and by thermodynamical calculations. The experimental conditions for pure 36°Y-X orientation growth have been optimized. The piezoelectricity of epitaxial 36°Y-X LiNbO3/SrTiO3/Si films was confirmed by means of piezoelectric force microscopy measurements and the ferroelectric domain inversion was attained at 85 kV.cm−1 as expected for the nearly stoichiometric LiNbO3. According to the theoretical calculations, 36°Y-X LiNbO3 films on Si could offer an electromechanical coupling of 24.4% for thickness extension excitation of bulk acoustic waves and a comparable figure of merit of actuators and vibrational energy harvesters to that of standard PbZr1− x Ti x O3 films. [ABSTRACT FROM AUTHOR]

van der Waals (vdW) heterogeneous integration and doping engineering have emerged as crucial factors in advancing the development of functional device systems. This work presents a fully vertical 2D/3D vdW stacking p‐MoxRe1‐xS2/GaN (x = 0.10 ± 0.02) heterojunction photodetector, integrating multiple strategies for enhanced performance, such as mixed‐dimensional stacking, p‐type doping, vertical device design, and type‐II band alignment. By integrating horizontal, vertical, and quasi‐vertical devices on a Free‐standing (FS)‐GaN substrate, the vertical p‐MoxRe1‐xS2/GaN device demonstrates superior performance, including high Ilight/Idark ratio (1.48 × 106), large Responsivity (888.69 AW−1), high specific detectivity (D*) (6.13 × 1014 Jones), and fast response speed (rise/decay time of 181 ms/259 ms). Moreover, the spectral response encompasses the ultraviolet (UV), visible, and near‐infrared (NIR) regions through energy band integration and bandgap modulation. This design surpasses previous devices, highlighting the potential of highly sensitive and micro‐integrated optoelectronic devices enabled by vertical vdW heterogeneous integration. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]