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The strain relaxation, surface morphology, and reflectivity of AlGaN‐distributed Bragg reflectors (DBRs) grown via metal–organic chemical vapor deposition on AlN/Al2O3 templates are investigated. Strain relaxation begins in a 10‐period Al0.50Ga0.50N (27 nm)/Al0.75Ga0.25N (29 nm) DBR, and the degree of strain relaxation (DSR) increases with the number of DBR periods. The 30‐period DBR exhibits a peak reflectivity of 0.82 at 279 nm, with a stopband of 12 nm. The DSR of n‐Al0.62Ga0.38N on the 30‐period DBR increases from 70% to 100% as the n‐Al0.62Ga0.38N thickness increases from 0.4 to 2.5 μm. Although the surface of a DBR comprises numerous spiral hillocks, n‐Al0.62Ga0.38N grown on an AlGaN DBR exhibits a step‐flow growth. A DSR of 100% with threading screw dislocations of 2.0 × 108 cm−2 and threading edge dislocations of 1.2 × 109 cm−2 is obtained for a 2.5 μm‐thick n‐Al0.62Ga0.38N on a 30‐period AlGaN DBR. [ABSTRACT FROM AUTHOR]

The size of in situ exsolved nanoparticles (NPs) significantly affects the electrochemical and electro‐catalytic properties of oxide supports. Unfortunately, the instrumental factor affecting the exsolved NP size in poly‐crystalline perovskite oxides is still unexplored. Herein, the inherent micro‐strain (ε) value as an unprecedented factor in controlling the exsolved NP size of Pr0.5Ba0.5‐xSrxFe0.85Ni0.15O3‐δ (x = 0.3, 0.4, and 0.5) is introduced, wherein smaller NP size is successfully obtained via strain relaxation strategy. The effect of exsolved NP size on the fuel oxidation reaction kinetics at high‐temperature regimes is evaluated in‐depth by using density functional theory (DFT) calculations. In accordance with the insights provided by DFT calculations, the electro‐catalyst featuring the smallest Fe3Ni NP size via strain relaxation strategy demonstrates exceptional electrochemical performance along with robust durability toward high‐temperature hydrogen oxidation reaction. This work presents scientific guidance for tailoring the exsolved NP size in perovskites, thereby paving the way for designing rational perovskite electro‐catalysts in various energy‐related applications. [ABSTRACT FROM AUTHOR]

The buried interface in the perovskite solar cell (PSC) has been regarded as a breakthrough to boost the power conversion efficiency and stability. However, a comprehensive manipulation of the buried interface in terms of the transport layer, buried interlayer, and perovskite layer has been largely overlooked. Herein, we propose the use of a volatile heterocyclic compound called 2‐thiopheneacetic acid (TPA) as a pre‐buried additive in the buried interface to achieve cross‐layer all‐interface defect passivation through an in situ bottom‐up infiltration diffusion strategy. TPA not only suppresses the serious interfacial nonradiative recombination losses by precisely healing the interfacial and underlying defects but also effectively enhances the quality of perovskite film and releases the residual strain of perovskite film. Owing to this versatility, TPA‐tailored CsPbBr3 PSCs deliver a record efficiency of 11.23% with enhanced long‐term stability. This breakthrough in manipulating the buried interface using TPA opens new avenues for further improving the performance and reliability of PSC. [ABSTRACT FROM AUTHOR]

Suppressing nonradiative recombination and releasing residual strain are prerequisites to improving the efficiency and stability of perovskite solar cells (PSCs). Here, long‐chain polyacrylic acid (PAA) is used to reinforce SnO2 film and passivate SnO2 defects, forming a structure similar to "reinforced concrete" with high tensile strength and fewer microcracks. Simultaneously, PAA is also introduced to the SnO2/perovskite interface as a "buffer spring" to release residual strain, which also acts as a "dual‐side passivation interlayer" to passivate the oxygen vacancies of SnO2 and Pb dangling bonds in halide perovskites. As a result, the best inorganic CsPbBr3 PSC achieves a champion power conversion efficiency of 10.83% with an ultrahigh open‐circuit voltage of 1.674 V. The unencapsulated PSC shows excellent stability under 80% relative humidity and 80°C over 120 days. [ABSTRACT FROM AUTHOR]

Abstract The buried interface in the perovskite solar cell (PSC) has been regarded as a breakthrough to boost the power conversion efficiency and stability. However, a comprehensive manipulation of the buried interface in terms of the transport layer, buried interlayer, and perovskite layer has been largely overlooked. Herein, we propose the use of a volatile heterocyclic compound called 2‐thiopheneacetic acid (TPA) as a pre‐buried additive in the buried interface to achieve cross‐layer all‐interface defect passivation through an in situ bottom‐up infiltration diffusion strategy. TPA not only suppresses the serious interfacial nonradiative recombination losses by precisely healing the interfacial and underlying defects but also effectively enhances the quality of perovskite film and releases the residual strain of perovskite film. Owing to this versatility, TPA‐tailored CsPbBr3 PSCs deliver a record efficiency of 11.23% with enhanced long‐term stability. This breakthrough in manipulating the buried interface using TPA opens new avenues for further improving the performance and reliability of PSC.

X‐ray diffraction from dislocation half‐loops consisting of a misfit segment with two threading arms extending from it to the surface is calculated by the Monte Carlo method. The diffraction profiles and reciprocal space maps are controlled by the ratio of the total lengths of the misfit and the threading segments of the half‐loops. A continuous transformation from the diffraction characteristic of misfit dislocations to that of threading dislocations with increasing thickness of epitaxial film is studied. Diffraction from dislocations with edge‐ and screw‐type threading arms is considered and the contributions of the two types of dislocations are compared. [ABSTRACT FROM AUTHOR]

Porous materials have been extensively used in electronic communications, aerospace, bio-medicine and petrochemical, etc. due to their attractive attributes such as low relative density, thermal and acoustical insulation and good permeability. Ultrashort laser pulses have a series of unique advantages including high energy density, ultrashort interaction time and high accuracy, which are widely used in the fields of precision machining and microelectronic manufacture. For porous materials heated by an ultrashort laser pulse, revealing the interplay between deformation field and temperature field is crucial to guide their engineering application and optimization design. The present work devotes to investigating the transient response of a porous half-space heated by a non-Gaussian laser beam on its boundary surface based on the newly established linear thermoelastic theory with strain and thermal relaxations. The coupled governing equations are formulated and solved through the Laplace transform and its numerical inversion. The distributions of the non-dimensional temperature, displacement, stress as well as volume fraction field are obtained and illustrated graphically. In calculation, the effects of the thermal relaxation factor, the strain relaxation factor on the temperature field, volume fraction field, displacement field as well as stress field are examined and discussed in detail. [ABSTRACT FROM AUTHOR]

The dependence of the performance of ultraviolet‐C (UV‐C) laser diodes on the strain relaxation of lower cladding layer (LCL) is numerically investigated. As the strain relaxation increases from 0% to 100%, the threshold current density decreases from 25 to 12.7 kA cm−2, and the slope efficiency increases from 0.039 to 0.087 W A−1, thanks to an increase in internal quantum efficiency (IQE). The improvement of IQE is mainly due to the enhanced hole injection resulting from the increased hole concentration in the distributed polarization doping layers and the reduced hole blocking barrier height of the upper waveguide layer with increasing the strain relaxation. Additionally, the effective screening of the polarization field within the quantum well ameliorates the quantum‐confined Stark effect, further improving the IQE. Our study reveals that strain relaxed LCL is imperative to achieve low‐threshold UV‐C laser diodes. [ABSTRACT FROM AUTHOR]

Tailoring crystal growth and defects in perovskites, a viable strategy for suppressing non‐radiative recombination, is widely employed for developing efficient and stable perovskite solar cells (PSCs). However, simultaneous tailoring of crystal growth and defects in PSCs is challenging owing to several limitations; for example, excessive interactions between additives and perovskite precursors impede crystallization, and additive‐induced impurity phases can substantially increase the defect density in perovskite films. In this study, we introduced a metal‐induced supersaturation‐suppression layer (SSL) as a pseudo‐additive interfacial layer to tailor the crystallization dynamics and defect formation in perovskite crystals in steps. The proposed perovskite modification process involves an SSL‐induced metal–halide ion reaction, which modulates the crystallization kinetics for grain growth and enables the formation of metal–halide complex anion adducts that can reduce crystalline defects and suppress non‐radiative recombination while facilitating preferential perovskite crystal growth by alleviating residual strains. Because of these stepwise synergistic effects, the SSL‐based PSCs exhibited significantly improved device performances (23.4%), low hysteresis losses, and enhanced atmospheric operational stability. [ABSTRACT FROM AUTHOR]

Abstract Suppressing nonradiative recombination and releasing residual strain are prerequisites to improving the efficiency and stability of perovskite solar cells (PSCs). Here, long‐chain polyacrylic acid (PAA) is used to reinforce SnO2 film and passivate SnO2 defects, forming a structure similar to “reinforced concrete” with high tensile strength and fewer microcracks. Simultaneously, PAA is also introduced to the SnO2/perovskite interface as a “buffer spring” to release residual strain, which also acts as a “dual‐side passivation interlayer” to passivate the oxygen vacancies of SnO2 and Pb dangling bonds in halide perovskites. As a result, the best inorganic CsPbBr3 PSC achieves a champion power conversion efficiency of 10.83% with an ultrahigh open‐circuit voltage of 1.674 V. The unencapsulated PSC shows excellent stability under 80% relative humidity and 80°C over 120 days.

Bandgap‐tunable mixed‐halide perovskite materials have attracted considerable interest because of their indispensability as top counterparts in tandem solar cells. However, the soft and disordered lattice always suffers from severe phase segregation under illumination, which is particularly susceptible to residual lattice strain. Herein, we report a strain regulation strategy by using alkenamides terminated Ti3C2Tx MXenes as an additive into perovskite precursor. Apart from the role of a template for grain growth to obtain high‐quality films, the stretchable alkyl chain promotes lattice shrinkage or expansion to form an elastic grain boundary to eliminate the spatially distributed stain and shut down ion migration channels. As a result, the all‐inorganic perovskite solar cells based on CsPbIBr2 and CsPbI2Br halides achieve prolonged device stability under harsh conditions and the best power conversion efficiencies up to 11.06% and 14.30%, respectively. [ABSTRACT FROM AUTHOR]

Abstract Bandgap‐tunable mixed‐halide perovskite materials have attracted considerable interest because of their indispensability as top counterparts in tandem solar cells. However, the soft and disordered lattice always suffers from severe phase segregation under illumination, which is particularly susceptible to residual lattice strain. Herein, we report a strain regulation strategy by using alkenamides terminated Ti3C2Tx MXenes as an additive into perovskite precursor. Apart from the role of a template for grain growth to obtain high‐quality films, the stretchable alkyl chain promotes lattice shrinkage or expansion to form an elastic grain boundary to eliminate the spatially distributed stain and shut down ion migration channels. As a result, the all‐inorganic perovskite solar cells based on CsPbIBr2 and CsPbI2Br halides achieve prolonged device stability under harsh conditions and the best power conversion efficiencies up to 11.06% and 14.30%, respectively.

Carbon-doped silicon (Si:C) thin films with C concentrations of 0.60% and 0.83% were fabricated into nanowires, and the lattice strain relaxation with shrinking the nanowire width, W, was evaluated in detail by x-ray reciprocal lattice space mapping (RSM) measurements. The obtained RSM profiles showed a right-downward distribution. From the RSM profiles, we considered that the lattice relaxation of the Si:C nanowires progressed slowly from the nanowires/substrate interfaces to the nanowire top surfaces. Then, we assumed the lattice strain of the Si:C thin films to be 100% and derived the average lattice strain relaxation of the Si:C nanowires from the RSM profiles. To derive the lattice relaxation, we summed the RSM profiles in the qx or qz directions, respectively, and calculated the average in-plane and out-of-plane lattice parameters. The obtained average lattice strain relaxation became larger with shrinking W, and progressed rapidly at W = 200 nm. Thus, we considered that the large strain relaxation occurs in the region of approximately 100 nm from the edge of the nanowires. In addition, the lattice strain relaxation was smaller for Si:C nanowires fabricated with their long side along the [100] direction than for Si:C nanowires along the [110] direction. We considered this difference of strain relaxation might be due to the crystallographic orientation dependence of Young's modulus. [ABSTRACT FROM AUTHOR]

The fabrication of high-efficiency GaAsP-based solar cells on GaAs wafers requires addressing structural issues arising from the materials lattice mismatch. We report on tensile strain relaxation and composition control of MOVPE-grown As-rich GaAs1−xPx/(100)GaAs heterostructures studied by double-crystal X-ray diffraction and field emission scanning electron microscopy. Thin (80–150 nm) GaAs1−xPx epilayers appear partially relaxed (within 1−12% of the initial misfit) through a network of misfit dislocations along the sample [ 011 ] and [ 01 1 − ] in plane directions. Values of the residual lattice strain as a function of epilayer thickness were compared with predictions from the equilibrium (Matthews–Blakeslee) and energy balance models. It is shown that the epilayers relax at a slower rate than expected based on the equilibrium model, an effect ascribed to the existence of an energy barrier to the nucleation of new dislocations. The study of GaAs1−xPx composition as a function of the V-group precursors ratio in the vapor during growth allowed for the determination of the As/P anion segregation coefficient. The latter agrees with values reported in the literature for P-rich alloys grown using the same precursor combination. P-incorporation into nearly pseudomorphic heterostructures turns out to be kinetically activated, with an activation energy EA = 1.41 ± 0.04 eV over the entire alloy compositional range. [ABSTRACT FROM AUTHOR]

The high porosity of a GaN porous structure (PS) makes it mechanically semi-flexible and can shield against the stress from the thick growth template on an overgrown layer to control the lattice structure or composition within the overgrown layer. To understand this stress shield effect, we investigated the lattice constant variations among different growth layers in various samples of overgrown Al0.3Ga0.7N on GaN templates under different strain-relaxation conditions based on d-spacing crystal lattice analysis. The fabrication of a strain-damping PS in a GaN template shields against the stress from the thick GaN template on the GaN interlayer, which lies between the PS and the overgrown AlGaN layer, such that the stress counteraction of the AlGaN layer against the GaN interlayer can reduce the tensile strain in AlGaN and increase its critical thickness. If the GaN interlayer is thin, such that a strong AlGaN counteraction occurs, the increased critical thickness can become larger than the overgrown AlGaN thickness. In this situation, crack-free, thick AlGaN overgrowth is feasible. [ABSTRACT FROM AUTHOR]

Mixed tin–lead perovskites suffer from structural instability and rapid tin oxidation; thus, the investigation of their optimal composition ranges is important to address these inherent weaknesses. The critical role of triple cations in mixed Sn–Pb iodides is studied by performing a wide range of compositional screenings over mechanochemically synthesized bulk and solution‐processed thin films. A ternary phase map of FA (Sn0.6Pb0.4)I3, MA(Sn0.6Pb0.4)I3, and Cs(Sn0.6Pb0.4)I3 is formed, and a promising composition window of (FA0.6−xMA0.4Csx)Sn0.6Pb0.4I3 (0 ≤ x ≤ 0.1) is demonstrated through phase, photoluminescence, and stability evaluations. Solar cell performance and chemical stability across the targeted compositional space are investigated, and FA0.55MA0.4Cs0.05Sn0.6Pb0.4I3 with strain‐relaxed lattices, reduced defect densities, and improved oxidation stability is demonstrated. The inverted perovskite solar cells with the optimal composition demonstrate a power conversion efficiency of over 22% with an open‐circuit voltage of 0.867 V, which corresponds to voltage loss of 0.363 V, promising for the development of narrow‐bandgap perovskite solar cells. [ABSTRACT FROM AUTHOR]

The atomic-layer misorientation during the growth of a 5 μm thick AlN thin film on a patterned (0001) sapphire substrate was investigated by the scan rotation approach using a probe aberration-corrected scanning transmission electron microscope at a nanometer scale. Through the geometrical phase analysis of the resulting twisted atomic structure at different depths below the top surface, it is shown that over 10% of local tensile and compressive strain is balanced in a 1.6° twist of the c-planes within the first micron of AlN growth. As a consequence, the formation of threading dislocations is reduced. The in-plane twist is seen to decrease toward the layer surface down to 0.5°. Finally, growth has adopted the conventional step flow mechanism with a reduced density of emerging dislocations by the thickness of 5 μm. Our finding forecasts the possibility of understanding the relationship between atomic bilayer twist and local strain accommodation at a nanometer scale, which could provide guidance for achieving better crystal quality of AlN thin films on patterned substrates during epitaxy. [ABSTRACT FROM AUTHOR]

Abstract Mixed tin–lead perovskites suffer from structural instability and rapid tin oxidation; thus, the investigation of their optimal composition ranges is important to address these inherent weaknesses. The critical role of triple cations in mixed Sn–Pb iodides is studied by performing a wide range of compositional screenings over mechanochemically synthesized bulk and solution‐processed thin films. A ternary phase map of FA (Sn0.6Pb0.4)I3, MA(Sn0.6Pb0.4)I3, and Cs(Sn0.6Pb0.4)I3 is formed, and a promising composition window of (FA0.6−xMA0.4Csx)Sn0.6Pb0.4I3 (0 ≤ x ≤ 0.1) is demonstrated through phase, photoluminescence, and stability evaluations. Solar cell performance and chemical stability across the targeted compositional space are investigated, and FA0.55MA0.4Cs0.05Sn0.6Pb0.4I3 with strain‐relaxed lattices, reduced defect densities, and improved oxidation stability is demonstrated. The inverted perovskite solar cells with the optimal composition demonstrate a power conversion efficiency of over 22% with an open‐circuit voltage of 0.867 V, which corresponds to voltage loss of 0.363 V, promising for the development of narrow‐bandgap perovskite solar cells.

Heteroepitaxial crystallographic tilt has been investigated as a possible strain‐relief mechanism in Al‐rich (Al>50%) AlGaN heteroepitaxial layers grown on single‐crystal (0001) AlN substrates with varying miscuts from 0.05° to 4.30°. The magnitude of the elastic lattice deformation‐induced tilt increases monotonically with the miscut angle, tightly following the Nagai tilt model. Although tilt angles as high as 0.1° are recorded, reciprocal space mapping (RSM) broadening and wafer bow measurements do not show any significant changes as a function of the heteroepitaxial tilt angle. While crystallographic tilting has been shown to be effective in controlling strain in some other heteroepitaxial systems, it does not provide any appreciable strain relief of the compressive strain in AlGaN/AlN heteroepitaxy. [ABSTRACT FROM AUTHOR]

Mg3Sb2-based compounds are one type of important room-temperature thermoelectric materials and the appropriate candidate of type-II nodal line semimetals. In Mg3Sb2-based films, compelling research topics such as dimensionality reduction and topological states rely on the controllable preparation of films with high crystallinity, which remains a big challenge. In this work, high quality Mg3Sb2 films are successfully grown on mismatched substrates of sapphire (000l), while the temperature-driven twin structure evolution and characteristics of the electronic structure are revealed in the as-grown Mg3Sb2 films by in situ and ex situ measurements. The transition of layer-to-island growth of Mg3Sb2 films is kinetically controlled by increasing the substrate temperature (Tsub), which is accompanied with the rational manipulation of twin structure and epitaxial strains. Twin-free structure could be acquired in the Mg3Sb2 film grown at a low Tsub of 573 K, while the formation of twin structure is significantly promoted by elevating the Tsub and annealing, in close relation to the processes of strain relaxation and enhanced mass transfer. Measurements of scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) elucidate the intrinsic p-type conduction of Mg3Sb2 films and a bulk band gap of ~0.89 eV, and a prominent Fermi level downshift of ~0.2 eV could be achieved by controlling the film growth parameters. As elucidated in this work, the effective manipulation of the epitaxial strains, twin structure and Fermi level is instructive and beneficial for the further exploration and optimization of thermoelectric and topological properties of Mg3Sb2-based films. [ABSTRACT FROM AUTHOR]

• Epitaxial anatase-type Nb:TiO 2 (TNO) thin films were transferred to flexible sheet. • Cracks were generated in epitaxial TNO thin films made using an earlier process. • The formation of cracks is attributed to the relaxation of epitaxial strain. • Use of the ductile polymer SU-8 3050 greatly inhibited cracking. • Electrical conductivity of epitaxial TNO thin films with fewer cracks was improved. This work developed a technique for fabricating flexible epitaxial thin films of anatase-type Nb:TiO 2 (epitaxial TNO) via a transfer process. In our prior work, epitaxial TNO deposited on LaAlO 3 (001) single crystal substrates was lifted off and affixed to flexible polymeric sheets. However, many cracks occurred on the surfaces of the transferred thin films, such that the conductivity of the epitaxial TNO was drastically decreased. This loss of conductivity was attributed to the interruption of current paths by the cracks. These numerous cracks were linear and in most cases were oriented either parallel to the [ 100 ] anatase ∥ [ 100 ] LAO direction or parallel to the [ 010 ] anatase ∥ [ 010 ] LAO direction (where the subscripts anatase and LAO represent the materials for each Miller index). Therefore, cracking likely occurred as a consequence of the relaxation of epitaxial strain and a return to the original axial lengths of the TNO during the transfer process. In the present work, the surface of epitaxial TNO was coated with the ductile polymer SU-8 3050 as a relaxation absorber prior to the transfer. This modified transfer process greatly reduced crack formation in the TNO such that the conductivity of the thin film was improved by two orders of magnitude. Thus, pre-coating with a ductile relaxation absorber was shown to effectively suppress the cracking of flexible epitaxial TNO. [ABSTRACT FROM AUTHOR]

SiN x interlayer was introduced in the epitaxial process of (11 2 ‾ 2) AlGaN film, and the influences of SiN x on the properties of (11 2 ‾ 2) AlGaN were characterized. It was revealed that the morphologic properties and crystal quality of (11 2 ‾ 2) AlGaN could be refined remarkably by optimizing SiN x growth time. Especially, a low root mean square value of 1.02 nm was obtained for S 3 with a SiN x growth time of 10 min, which was 56.7 % less than S 0 that grown without SiN x. Meanwhile, compared with S 0 , the full width at half maximum values of X-ray rocking curves for S 3 were reduced by 39.6 % along [11 2 ‾ 3 ‾ ] direction and 41.2 % along [1 1 ‾ 00 ] direction. Besides, the background electron concentration and basal stacking faults related emission of (11 2 ‾ 2) AlGaN could also be suppressed remarkably by optimizing SiN x growth time to 10 min. These improvements could be originated from the formation of SiN x islands, leading to the lateral growth of AlGaN overlayer, the relaxation of strain in the AlGaN, and the annihilation of dislocations. [ABSTRACT FROM AUTHOR]

We investigate in detail the role of strain relaxation and capping overgrowth in the self-assembly of InAs quantum dots by droplet epitaxy. InAs quantum dots were realized on an In 0.6 Al 0.4 As metamorphic buffer layer grown on a GaAs(111)A misoriented substrate. The comparison between the quantum electronic calculations of the optical transitions and the emission properties of the quantum dots highlights the presence of a strong quenching of the emission from larger quantum dots. Detailed analysis of the surface morphology during the capping procedure show the presence of a critical size over which the quantum dots are plastically relaxed. [ABSTRACT FROM AUTHOR]

Although the photovoltaic performance of perovskite solar cells (PSCs) has reached the commercial standards, the unsatisfactory stability limits their further application. Hydrophobic interface and encapsulation can block the damage of water and oxygen, while the instability induced by intrinsic residual strain remains inevitable. Here, the residual strain in a two‐dimensional (2D) Ruddlesden–Popper (RP) perovskite film is investigated by X‐ray diffraction and atomic force microscopy. It's found that the spacer cations contribute to the residual strain even though they are not in the inorganic cages. Benefited from strain relaxation, the film quality is improved, leading to suppressed recombination, promoted charge transport and enhanced efficiency. More significantly, the strain‐released devices maintain 86 % of the initial efficiency after being kept in air with 85 % relative humidity (RH) for 1080 h, 82 % under maximum power point (MPP) tracking at 50 °C for 804 h and 86 % after continuous heating at 85 °C for 1080 h. [ABSTRACT FROM AUTHOR]

A three-dimensional kinetic Monte Carlo methodology is developed to study the strained epitaxial growth of wurtzite GaN/AlN quantum dots. It describes the kinetics of effective GaN adatoms on an hexagonal lattice. The elastic strain energy is evaluated by a purposely devised procedure: first, we take advantage of the fact that the deformation in a lattice-mismatched heterostructure is equivalent to that obtained by assuming that one of the regions of the system is subjected to a properly chosen uniform stress (Eshelby inclusion concept), and then the strain is obtained by applying the Green's function method. The standard Monte Carlo method has been modified to implement a multiscale algorithm that allows the isolated adatoms to perform long diffusion jumps. With these state-of-the art modifications, it is possible to perform efficiently simulations over large areas and long elapsed times. We have taylored the model to the conditions of molecular beam epitaxy under N-rich conditions. The corresponding simulations reproduce the different stages of the Stranski–Krastanov transition, showing quantitative agreement with the experimental findings concerning the critical deposition, and island size and density. The influence of growth parameters, such as the relative fluxes of Ga and N and the substrate temperature, is also studied and found to be consistent with the experimental observations. In addition, the growth of stacked layers of quantum dots is also simulated and the conditions for their vertical alignment and homogenization are illustrated. In summary, the developed methodology allows one to reproduce the main features of the self-organized quantum dot growth and to understand the microscopic mechanisms at play. [ABSTRACT FROM AUTHOR]

Semipolar (11 2 ¯ 2) InGaN/GaN superlattice templates with different periodical InGaN layer thicknesses were grown on m-plane sapphire substrates using metal-organic chemical vapor deposition (MOCVD). The strain in the superlattice layers, the relaxation mechanism and the influence of the strain relaxation on the semipolar superlattice template were explored. The results demonstrated that the strain in the (11 2 ¯ 2) InGaN/GaN superlattice templates was anisotropic and increased with increasing InGaN thickness. The strain relaxation in the InGaN/GaN superlattice templates was related to the formation of one-dimension misfit dislocation arrays in the superlattice structure, which caused tilts in the superlattice layer. Whereas, the rate of increase of the strain became slower with increasing InGaN thickness and new misfit dislocations emerged, which damaged the quality of the superlattice relaxed templates. The strain relaxation in the superlattice structure improved the surface microtopography and increased the incorporation of indium in the InGaN epitaxial layers. [ABSTRACT FROM AUTHOR]

Binary rutile oxides of 5d metals such as IrO 2 stand out in comparison to their 3d and 4d counterparts due to limited experimental studies, despite rich predicted quantum phenomena. Here, we investigate the electrical transport properties of IrO 2 by engineering epitaxial thin films grown using hybrid molecular beam epitaxy. Our findings reveal phonon-limited carrier transport and thickness-dependent anisotropic in-plane resistance in IrO 2 (110) films, the latter suggesting a complex relationship between strain relaxation and orbital hybridization. Magnetotransport measurements reveal a previously unobserved nonlinear Hall effect. A two-carrier analysis of this effect shows the presence of minority carriers with mobility exceeding 3000 cm 2 /(V s) at 1.8 K. These results point toward emergent properties in 5d metal oxides that can be controlled using dimensionality and epitaxial strain.

The fabrication of high-efficiency GaAsP-based solar cells on GaAs wafers requires addressing structural issues arising from the materials lattice mismatch. We report on tensile strain relaxation and composition control of MOVPE-grown As-rich GaAs1−xPx/(100)GaAs heterostructures studied by double-crystal X-ray diffraction and field emission scanning electron microscopy. Thin (80–150 nm) GaAs1−xPx epilayers appear partially relaxed (within 1−12% of the initial misfit) through a network of misfit dislocations along the sample [011] and [011−] in plane directions. Values of the residual lattice strain as a function of epilayer thickness were compared with predictions from the equilibrium (Matthews–Blakeslee) and energy balance models. It is shown that the epilayers relax at a slower rate than expected based on the equilibrium model, an effect ascribed to the existence of an energy barrier to the nucleation of new dislocations. The study of GaAs1−xPx composition as a function of the V-group precursors ratio in the vapor during growth allowed for the determination of the As/P anion segregation coefficient. The latter agrees with values reported in the literature for P-rich alloys grown using the same precursor combination. P-incorporation into nearly pseudomorphic heterostructures turns out to be kinetically activated, with an activation energy EA = 1.41 ± 0.04 eV over the entire alloy compositional range.

This work investigated the electrical properties in AlGaN/GaN/Si HEMTsgrown by molecular beam epitaxy. The electrical behavior have been investigated using by electric permittivity, modulus formalism and conductance measurements. As has been found from electrical conductance, dispersive behavior is related to barrier inhomogeneity and deep trap in barrier layer. On the other hand, the strain relaxation of charge transport is studied both permittivity and electric modulus formalisms. [ABSTRACT FROM AUTHOR]

In this paper, the edge strain relaxation of InGaN/GaN MQW micro-pillars is studied. Micro-pillar arrays with a diameter of 3–20 μm were prepared on a blue GaN LED wafer by inductively coupled plasma (ICP) etching. The peak wavelength shift caused by edge strain relaxation was tested using micro-LED pillar array room temperature photoluminescence (PL) spectrum measurements. The results show that there is a nearly 3 nm peak wavelength shift between the micro-pillar arrays, caused by a high range of the strain relaxation region in the small size LED pillar. Furthermore, a 19 μm micro-LED pillar's Raman spectrum was employed to observe the pillar strain relaxation. It was found that the Raman E2H mode at the edge of the micro-LED pillar moved to high frequency, which verified an edge strain relaxation of = 0.1%. Then, the exact strain and peak wavelength distribution of the InGaN quantum wells were simulated by the finite element method, which provides effective verification of our PL and Raman strain relaxation analysis. The results and methods in this paper provide good references for the design and analysis of small-size micro-LED devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • This work presents a multistage growth model to understand vertical as well as spatial growth of Vertical Graphene Nanowalls (VGN). • VGN was grown on Si substrate using RF-PECVD for 15 min., 30 min., 60 min., 120 min. & 240 min. • The synthesized VGN samples were investigated using IP-GIXRD, Raman spectroscopy, SEM, and AFM microscopy. • The strain relaxation followed by defect annihilation and continuous increase in crystallite size plays a crucial role in growth of VGN with time. • A schematic diagram presented showing correlation between mediating factors at each stage responsible for growth of VGN with time. This work presents a time dependent multistage growth model for vertical graphene nanowalls (VGN). Factors mediating growth of VGN in both vertical and spatial direction at different stages were discussed. VGN films were deposited on Si (100) substrate using Radio Frequency Plasma-Enhanced Chemical Vapor Deposition technique by increasing the deposition time systematically for 15 min, 30 min, 60 min, 120 min, and 240 min, respectively. Scanning electron microscopy was carried out in both planar and cross section view to confirm the growth of VGN and quantification of its height. Atomic force microscopy was used to characterize the spatial growth of VGN. Raman scattering and in-plane GIXRD measurements were carried out to characterize the microstructure of VGN, which unveils that the strain relaxation and defects annihilation followed by increase in average crystallite size plays crucial role. Eventually, a schematic diagram was presented for time dependent evolution of VGN at different stages. [ABSTRACT FROM AUTHOR]

The high porosity of a GaN porous structure (PS) makes it mechanically semi-flexible and can shield against the stress from the thick growth template on an overgrown layer to control the lattice structure or composition within the overgrown layer. To understand this stress shield effect, we investigated the lattice constant variations among different growth layers in various samples of overgrown Al0.3Ga0.7N on GaN templates under different strain-relaxation conditions based on d-spacing crystal lattice analysis. The fabrication of a strain-damping PS in a GaN template shields against the stress from the thick GaN template on the GaN interlayer, which lies between the PS and the overgrown AlGaN layer, such that the stress counteraction of the AlGaN layer against the GaN interlayer can reduce the tensile strain in AlGaN and increase its critical thickness. If the GaN interlayer is thin, such that a strong AlGaN counteraction occurs, the increased critical thickness can become larger than the overgrown AlGaN thickness. In this situation, crack-free, thick AlGaN overgrowth is feasible.

[Display omitted] • Bonding interface is modified to a homogenous one with an epitaxial layer. • Epitaxial layer constrains the defects, disperses and reduces the heterogenous mismatch stress. • Epitaxial layer is doped to reduce the carrier recombination leakage current in this defect-rich layer. In the realm of optoelectronic integration, silicon-based Ge bonding has attracted great attention due to its advantages in short-wave infrared response and low cost. However, owing to the inherent lattice mismatch and thermal mismatch between Ge and Si, the bonded Ge-Si heterogenous interfaces encountered problems of thermal instability and high interface states. Herein, an approach of separating the bonding interface from the heterogenous interface is proposed through inserting a Ge epitaxial layer (GeEL) between the Si substrate and Ge film. This separation modifies the bonding interface to a homogenous one, alleviating the massive mismatch stress and achieving film relaxation, enhancing bonding stability in all aspects. Moreover, during 850 °C annealing, GeEL is doped via diffusion hence realizes electric filed modulation, inhibiting the carrier recombination leakage current and trap assisted tunneling in this defect-rich layer. A Ge-Si heterogenous PIN diode prepared by this bonding method has achieved a remarkable low dark current density (1.33 mA/cm2), a low ideality factor (1.11), and a high on–off ratio (1 0 6), confirming the outstanding quality of the bonded heterojunction. This work provides great prospects for higher performance, larger scale and multi-functional Si-based heterogenous material device applications. [ABSTRACT FROM AUTHOR]

The research on strain in epitaxial thin films has attracted lots of attention since strain in semiconductors may significantly affect the quality of materials and the performance of devices. In this work, we focus on the strain in ε -Ga 2 O 3 thin films grown by metal-organic chemical vapor deposition (MOCVD) on c-plane sapphire substrates. Combining X-ray Diffraction and wafer bowing measurements, it is confirmed that all the ε -Ga 2 O 3 epi-films exhibit tensile stress in ∼1 GPa level. Vicinal surface epitaxy (VSE) is adopted in order to relax the tensile stress in ε -Ga 2 O 3 thin films. As the substrate miscut angle increases from 0.2 ° to 6 °, the stress is effectively reduced from 1.29 GPa to 0.68 GPa. It is also found that the strain relaxation by VSE is accompanied by defect generation and lattice tilt in the epitaxial film. A qualitative model is proposed to explain the mechanisms of strain relaxation and defect formation in the VSE of ε- Ga 2 O 3 /c-sapphire structure. Therefore, the VSE could be considered as an effective strategy for strain relaxation in ε -Ga 2 O 3 heteroepitaxial film. • The residual stress in the epitaxial ε -Ga 2 O 3 /sapphire structures is evaluated. • Introducing a miscut angle on the substrate is an effective method for strain relaxation in ε -Ga 2 O 3 heteroepitaxy. • A qualitative strain relaxation model based on the miscut-induced unbalanced nucleation of dislocations was proposed. [ABSTRACT FROM AUTHOR]

The residual strain induced during the growth of perovskite film is an intrinsic issue that significantly affects the efficiency and stability of perovskite solar cells (PVSCs). Inspired by the flipped annealing method to release strain in perovskite thin films, SiO2‐coated gold nanorods (GNR@SiO2) are introduced into perovskite film and advantage of the plasmonic local heating effect is taken for in situ strain relaxation. The GNR@SiO2‐incorporated inverted PVSCs exhibit a champion power conversion efficiency (PCE) over 23%, which is the highest PCE in plasmonic‐incorporated PVSCs. Moreover, the intrinsic stability of the resulting PVSCs is greatly improved for the nonencapsulated device and retains 84% of its initial PCE after 2800 h aging under continuous illumination at 65 ± 5 °C in an N2 glove box and nearly 90% after 1000 h repetitive 12 h light on–off cycles. This work provides an efficient yet easy‐to‐implement plasmonic heating strategy for simultaneously enhancing the efficiency and stability of PVSCs. [ABSTRACT FROM AUTHOR]

Ge/Si(001) multilayer heterostructures containing arrays of low‐temperature self‐assembled Ge quantum dots and very thin SixGe1−x layers of varying composition and complex geometry have been studied using Raman spectroscopy and scanning tunneling microscopy (STM). The dependence of Raman spectra on the effective thickness of deposited Ge layers has been investigated in detail in the range from 4 to 18 Å. The position and shape of both Ge and SiGe vibrational modes are of great interest because they are closely related to the strain and composition of the material that plays a role of active component in perspective optoelectronic devices based on such structures. In this work, we present an explanation for some peculiar features of Raman spectra, which makes it possible to control the quality of the grown heterostructures more effectively. A dramatic increase of intensity of both the Ge–Ge and Si–Ge bands for the structure containing Ge layers of 10 Å and anomalous shift and broadening of the Si–Ge band for structures comprising Ge layers of 8 and 9 Å thick were observed. In our model, the anomalous behavior of the Raman spectra with the change of thickness of deposited Ge is connected with the flatness of Ge layers as well as transitional SiGe domains formed via the stress‐induced diffusion from {105} facets of quantum dots. The conclusions are supported by the STM studies and the numerical calculations. [ABSTRACT FROM AUTHOR]

Few layered graphite oxide (GO) is synthesized from soft graphite using nitric acid as a strong oxidizing agent. The citrate reduction method is used to prepare gold nanoparticles (AuNPs). AuNPs are incorporated in GO with assorted atomic-mass ratios in between 0.02 and 1.0%. The as-prepared AuNPs/GO nanocomposites are thoroughly characterized by micro-Raman spectroscopy (MRS), high-resolution X-ray photoelectron spectroscopy (HRXPS), and micro-photoluminescence (MPL). MRS study confirms the presence of a GO-related strain relaxation process arising from sp2 to sp3 conformational change in the carbon bonding of the AuNPs/GO. HRXPS studies confirm the presence of CO species in GO samples along with a strong interaction between the two constituents in AuNPs/GO samples. The HRXPS study substantiates electronic transfer from GO to AuNPs constituents during the composite formation. In addition, the intrinsic surface plasmonic mode of AuNPs is also found in AuNPs/GO from the MPL studies. Electrochemical measurements confirm a higher anticorrosive nature of AuNPs/GO-1.0% electrode at fluorine tin oxide conductive glass surface in respect to GO electrode and that is ascribed to the nanocomposites' 5d106s1 configuration related lesser catalytic activity. The catalytic activity of AuNPs/GO catalyst nanocomposites upon elimination of hydroxyl radicals formed in an ethanol oxidation system was examined using the electrochemical impedance method. Finally, the prospects of high-performance anticorrosive protective layer applications are also discussed in this paper. [ABSTRACT FROM AUTHOR]

Red phosphorus (RP), as a promising anode for potassium‐ion batteries (KIBs), and has attracted extensive attention due to its high theoretical capacity, low redox potential, and abundant natural sources. However, RP shows dramatic capacity decay and rapid structure degradation caused by huge volume expansion and poor electronic conductivity. Here, a volume strain‐relaxation electrode structure is reported, by encapsulating well‐confined amorphous RP in 3D interconnected sulfur, nitrogen co‐doped carbon nanofibers (denoted as RP@S‐N‐CNFs). In situ transmission electron microscopy and the corresponding chemo‐mechanical simulation reveal the excellent structural integrity and robustness of the N, S carbon matrix. As a freestanding anode for KIBs, the RP@S‐N‐CNFs electrode exhibits high reversible capacities (566.7 mAh g−1 after 100 cycles at 0.1 A g−1) and extraordinary durability (282 mAh g−1 after 2000 cycles at 2 A g−1). The highly reversible one‐electron transfer mechanism with a final discharge product of KP and faster kinetics are demonstrated through in situ characterizations and density functional theory calculations. This work sheds light on the rational design of large‐volume‐vibration type anodes for next‐generation high‐performance KIBs. [ABSTRACT FROM AUTHOR]

Viscoelastic laminated sandwich composite structure has been used as a new class of high-efficient structural damping in the passive vibration control systems. This work aims to investigate transient thermo-viscoelastic responses of viscoelastic laminated sandwich composite structure. The effects of fractional order parameters and material constants ratio on the structural transient thermo-viscoelastic responses are evaluated and discussed. For each homogeneous isotropic layer, the governing equations are formulated and solved by Laplace transformation techniques. The results are expected to provide new insights on the vibration control and thermal management of viscoelastic laminated sandwich composite structure under extreme non-isothermal conditions. [ABSTRACT FROM AUTHOR]

Three similar‐structure InGaN/AlGaN multiple‐quantum‐well near‐ultraviolet (NUV) light‐emitting diodes (LEDs) are utilized to investigate the microscopic effect of defects on strain relaxation. Consistent correlations among the crystal quality, the piezoelectric field (FPZ), the internal quantum efficiency (IQE), and the bandgap shrinkage of NUV LEDs are obtained by investigating the macroscopic characterizations. The difference in crystal quality (or the defect density) of NUV LEDs is found by the ideality factor, the emission microscope image, the Shockley–Read–Hall coefficient, and the IQE. Electroreflectance spectra are used to calculate FPZ of NUV LEDs. FPZ, the IQE, and the peak‐wavelength shift at driving currents are increased with the samples' crystal quality compared to the reference sample. Also, FPZ, the IQE, and the peak‐wavelength shift are decreased with the increase in samples' defect densities. A similar result is found for the bandgap shrinkage. This effect significantly indicates that the strain relaxation is induced by defects. Herein, a model that systematically explains the observed changes in macroscopic properties of NUV LEDs is proposed. [ABSTRACT FROM AUTHOR]

Flexoelectricity has become an emerging tool to tailor the material properties. The flexoelectric modulation of ferroelectric photovoltaic (FEPV) properties is of particular interest, because it offers an opportunity to boost the photovoltaic efficiency. In most previous studies, the flexoelectric effect is generated by local pressing or macroscopic bending, which, however, results in a local or weak modulation of the FEPV behavior. Here, a significant modulation of the FEPV effect by the strain‐relaxed epitaxy (SRE)‐induced giant macroscopic flexoelectric effect is demonstrated. Using SRE, giant strain gradients (>107 m−1) are generated and tuned in ferroelectric Pb(Zr0.2Ti0.8)O3 epitaxial films. Tuning the giant strain gradient can significantly modify the switchable FEPV properties. Particularly, a photovoltage enhancement as large as ≈0.5 V is achieved. It is suggested that the flexoelectric modulation of FEPV behavior may originate from the flexoelectric polarization‐induced depolarization field. This study highlights the immense application potential of the SRE‐induced flexoelectricity in the engineering of functional thin‐film devices. [ABSTRACT FROM AUTHOR]

Abstract Characteristics of atomic layer deposition (ALD)-grown ZnO thin films on sapphire substrates with and without three-pulsed ozone (O3) as oxidant precursor and post-deposition thermal annealing (TA) are investigated. Deposition temperature and thickness of ZnO epilayers are 180 °C and 85 nm, respectively. Post-deposition thermal annealing is conducted at 300 °C in the ambience of oxygen (O2) for 1 h. With strong oxidizing agent O3 and post-deposition TA in growing ZnO, intrinsic strain and stress are reduced to 0.49% and 2.22 GPa, respectively, with extremely low background electron concentration (9.4 × 1015 cm−3). This is originated from a lower density of thermally activated defects in the analyses of thermal quenching of the integrated intensity of photoluminescence (PL) spectra. TA further facilitates recrystallization forming more defect-free grains and then reduces strain and stress state causing a remarkable decrease of electron concentration and melioration of surface roughness.

Abstract GeSn is a promising material for the fabrication of on-chip photonic and nanoelectronic devices. Processing techniques dedicated to GeSn have thus been developed, including epitaxy, annealing, ion implantation, and etching. In this work, suspended, strain-relaxed, and high-quality GeSn microdisks are realized by a new approach without any etching to GeSn alloy. The GeSn alloy was grown on pre-patterned Ge (001) substrate by molecular beam epitaxy at low temperatures. The transmission electron microscopy and scanning electron microscopy were carried out to determine the microstructures of the GeSn samples. The microdisks with different diameters of Ge pedestals were fabricated by controlling the selective wet etching time, and micro-Raman results show that the microdisks with different dimensions of the remaining Ge pedestals have different extents of strain relaxation. The compressive strain of microdisks is almost completely relaxed under suitable conditions. The semiconductor processing technology presented in this work can be an alternative method to fabricate innovative GeSn and other materials based micro/nano-structures for a range of Si-compatible photonics, 3D-MOSFETs, and microelectromechanical device applications.

Mg3Sb2-based compounds are one type of important room-temperature thermoelectric materials and the appropriate candidate of type-II nodal line semimetals. In Mg3Sb2-based films, compelling research topics such as dimensionality reduction and topological states rely on the controllable preparation of films with high crystallinity, which remains a big challenge. In this work, high quality Mg3Sb2 films are successfully grown on mismatched substrates of sapphire (000l), while the temperature-driven twin structure evolution and characteristics of the electronic structure are revealed in the as-grown Mg3Sb2 films by in situ and ex situ measurements. The transition of layer-to-island growth of Mg3Sb2 films is kinetically controlled by increasing the substrate temperature (Tsub), which is accompanied with the rational manipulation of twin structure and epitaxial strains. Twin-free structure could be acquired in the Mg3Sb2 film grown at a low Tsub of 573 K, while the formation of twin structure is significantly promoted by elevating the Tsub and annealing, in close relation to the processes of strain relaxation and enhanced mass transfer. Measurements of scanning tunneling spectroscopy (STS) and angle-resolved photoemission spectroscopy (ARPES) elucidate the intrinsic p-type conduction of Mg3Sb2 films and a bulk band gap of ~0.89 eV, and a prominent Fermi level downshift of ~0.2 eV could be achieved by controlling the film growth parameters. As elucidated in this work, the effective manipulation of the epitaxial strains, twin structure and Fermi level is instructive and beneficial for the further exploration and optimization of thermoelectric and topological properties of Mg3Sb2-based films.

We investigate in detail the role of strain relaxation and capping overgrowth in the self-assembly of InAs quantum dots by droplet epitaxy. InAs quantum dots were realized on an In0.6Al0.4As metamorphic buffer layer grown on a GaAs(111)A misoriented substrate. The comparison between the quantum electronic calculations of the optical transitions and the emission properties of the quantum dots highlights the presence of a strong quenching of the emission from larger quantum dots. Detailed analysis of the surface morphology during the capping procedure show the presence of a critical size over which the quantum dots are plastically relaxed.

A three-dimensional kinetic Monte Carlo methodology is developed to study the strained epitaxial growth of wurtzite GaN/AlN quantum dots. It describes the kinetics of effective GaN adatoms on an hexagonal lattice. The elastic strain energy is evaluated by a purposely devised procedure: first, we take advantage of the fact that the deformation in a lattice-mismatched heterostructure is equivalent to that obtained by assuming that one of the regions of the system is subjected to a properly chosen uniform stress (Eshelby inclusion concept), and then the strain is obtained by applying the Green’s function method. The standard Monte Carlo method has been modified to implement a multiscale algorithm that allows the isolated adatoms to perform long diffusion jumps. With these state-of-the art modifications, it is possible to perform efficiently simulations over large areas and long elapsed times. We have taylored the model to the conditions of molecular beam epitaxy under N-rich conditions. The corresponding simulations reproduce the different stages of the Stranski–Krastanov transition, showing quantitative agreement with the experimental findings concerning the critical deposition, and island size and density. The influence of growth parameters, such as the relative fluxes of Ga and N and the substrate temperature, is also studied and found to be consistent with the experimental observations. In addition, the growth of stacked layers of quantum dots is also simulated and the conditions for their vertical alignment and homogenization are illustrated. In summary, the developed methodology allows one to reproduce the main features of the self-organized quantum dot growth and to understand the microscopic mechanisms at play.