Dislocation Bending Research Articles

Effective InAsP dislocation filtering layers for InP heteroepitaxy on CMOS-standard (001) silicon

In this work, we report InAsP-based dislocation filter layers (DFLs) for InP heteroepitaxy on CMOS-standard (001) Si substrates, demonstrating a threading dislocation density of 3.7 × 107 cm−2. The strain introduced by InAsP induces dislocation bending at the InAsP/InP interface, thereby facilitating the reaction and annihilation of dislocations during their lateral glide. Concurrently, the InP spacer exhibits tensile strain, leading to the formation of stacking faults (SFs). With a comprehensive analysis utilizing x-ray diffraction, electron channeling contrast imaging, and transmission electron microscopy, the effects of DFL-induced strain on dislocations and SFs are investigated. Fine-tuning the strain conditions allowed low-dislocation-density while SF-suppressed, anti-phase boundary free InP on Si. This work, therefore, provides a useful buffer engineering scheme for monolithic integration of InP-based electronic and photonic devices onto the industry-standard silicon platform.

Plastic Shakedown Behavior and Deformation Mechanisms of Ti17 Alloy under Long Term Creep–Fatigue Loading

Ti17 alloy is mainly used to manufacture aero-engine discs due to its excellent properties such as high strength, toughness and hardenability. It is often subjected to creep–fatigue cyclic loading in service environments. Shakedown theory describes the state in which the accumulated plastic strain of the material stabilizes after several cycles of cyclic loading, without affecting its initial function and leading to failure. This theory includes three behaviors: elastic shakedown, plastic shakedown and ratcheting. In this paper, the creep–fatigue tests (CF) were conducted on Ti17 alloy at 300 °C to study its shakedown behavior under creep–fatigue cyclic loading. Based on the plasticity–creep superposition model, a theory model that accurately describes the shakedown behavior of Ti17 alloy was constructed, and ABAQUS finite element software was used to validate the accuracy of the model. TEM analysis was performed to observe the micro-mechanisms of shakedown in Ti17 alloy. The results reveal that the Ti17 alloy specimens exhibit plastic shakedown behavior after three cycles of creep–fatigue loading. The established finite element model can effectively predict the plastic shakedown process of Ti17 alloy, with a relative error between the experimental and simulation results within 4%. TEM results reveal that anelastic recovery controlled by dislocation bending and back stress hardening caused by inhomogeneous deformation are the main mechanisms for the plastic shakedown behavior of Ti17 alloy.

Analysis of dislocation defects in compositionally step-graded α-(Al x Ga1-x )2O3 layers.

The ultra-wide bandgap semiconductor α-Ga2O3 can be heteroepitaxially grown on a sapphire substrate. However, due to a lattice mismatch of about 4.6% with a sapphire substrate, many dislocation defects occur in α-Ga2O3 films. To reduce the dislocation density, compositionally step-graded α-(Al x Ga1-x )2O3 layers were fabricated on a c-plane sapphire substrate using mist CVD. TEM measurements revealed few dislocations in the initial layer of α-(Al0.96Ga0.04)2O3, but numerous dislocations were observed in the subsequent layer of α-(Al0.84Ga0.16)2O3. However, the step-graded α-(Al x Ga1-x )2O3 layers exhibited bending of the dislocations under both compressive and tensile strains due to compositional differences of α-(Al x Ga1-x )2O3, resulting in about 50% reduction of the dislocation density in the high-Ga-composition layer of α-(Al x Ga1-x )2O3. The introduction of multiple 50 nm α-Ga2O3 layers into the compositionally step-graded α-(Al x Ga1-x )2O3 layers resulted in a notable reduction in dislocation defects at the interface between the sandwiched α-Ga2O3 layers. It is assumed that the dislocations were bent by the strain caused by the composition change, resulting in a decrease in the number of dislocations. It is anticipated that further reduction of dislocation density will be achieved by optimizing the composition change and thicknesses of layers that provide effective strain for dislocation bending, and by stacking these layers.

SiCp/AlSi10Mg composites with simultaneously enhanced tensile strength and ductility fabricated by laser powder bed fusion additive manufacturing

Currently, SiCp/Al composites fabricated by laser powder bed fusion (LPBF) suffer from poor plasticity caused by their low density and a great deal of coarse needle-like brittle phases, which seriously limits their application in aerospace field. High scanning speed can shorten the reaction time between SiC and Al liquid due to the short existence time of molten pool, effectively suppressing the nucleation and growth of these needle-like brittle phases. Therefore, an LPBF with a high-speed scanning printing strategy was proposed to fabricate micro-SiCp/Al composites in this study. The effects of energy density (E) on the densification, microstructure and mechanical properties of the composites were studied systematically. The contradiction that the higher the density, the more and coarser needle-like phases produced was successfully resolved. The micro-SiCp/Al composites with simultaneously enhanced strength and ductility were achieved at a proper E of 47 J/mm3, whose tensile strength and elongation reached 356.7 ± 5.0 MPa and 11.6 ± 0.4%, respectively. Among them, the elongation is almost 4 times the maximum value reported in the literature, which is mainly attributed to the extremely high compactness without any visible defects, the moderate dissolution and uniform distribution of SiC particles, the refined grains, a few nano-sized Al4C3 and Al4SiC4, and the interfacial structure SiC–Al4SiC4–Al with high interfacial bonding strength. Because these factors greatly reduced the stress concentration inside the composites and made the stress evenly distributed during loading, thus improving the ductility. Especially these in-situ synthesized Al4C3 and Al4SiC4 can not only promote the transformation of α-Al columnar grains to cellular grains, but also hinder the bending and motion of dislocations, playing a role in grain refinement and dispersion strengthening. The fracture mode of the composites is ductile fracture. Our work provides theoretical guidance and technical support for fabricating SiCp/Al composites with simultaneously enhanced strength and ductility.

Ferroelectric Switching at Symmetry-Broken Interfaces by Local Control of Dislocations Networks.

Semiconducting ferroelectric materials with low energy polarization switching offer a platform for next-generation electronics such as ferroelectric field-effect transistors. Recently discovered interfacial ferroelectricity in bilayers of transition metal dichalcogenide films provides an opportunity to combine the potential of semiconducting ferroelectrics with the design flexibility of 2D material devices. Here, local control of ferroelectric domains in a marginally twisted WS2 bilayer is demonstrated with a scanning tunneling microscope at room temperature, and their observed reversible evolution is understood using a string-like model of the domain wall network (DWN). Two characteristic regimes of DWN evolution are identified: (i) elastic bending of partial screw dislocations separating smaller domains with twin stackings due to mutual sliding of monolayers at domain boundaries and (ii) merging of primary domain walls into perfect screw dislocations, which become the seeds for the recovery of the initial domain structure upon reversing electric field. These results open the possibility to achieve full control over atomically thin semiconducting ferroelectric domains using local electric fields, which is a critical step towards their technological use.

Mechanical Spectroscopy Study of CrNiCoFeMn High-Entropy Alloys.

The equiatomic high-entropy alloy of composition of CrNiCoFeMn with an FCC crystal structure was prepared by either induction melting or additive manufacturing with a selective laser melting (SLM) process, starting from mechanically alloyed powders. The as-produced samples of both kinds were cold worked, and in some cases re-crystallized. Unlike induction melting, there is a second phase, which is made of fine nitride and Cr-rich σ phase precipitates, in the as-produced SLM alloy. Young's modulus and damping measurements, as a function of temperature in the 300-800 K range, were performed on the specimens that were cold-worked and/or re-crystallized. Young's modulus values of (140 ± 10) GPa and (90 ± 10) GPa were measured from the resonance frequency of free-clamped bar-shaped samples at 300 K for the induction-melted and SLM samples, respectively. The room temperature values increased to (160 ± 10) GPa and (170 ± 10) GPa for the re-crystallized samples. The damping measurements showed two peaks, which were attributed to dislocation bending and grain-boundary sliding. The peaks were superposed on an increasing temperature background.

Homoepitaxy Growth of High‐Quality AlN Film on MOCVD AlN Template by Hydride Vapor Phase Epitaxy

Herein, AlN film grown on metal‐organic chemical vapor deposition (MOCVD) AlN template by high‐temperature hydride vapor phase epitaxy (HVPE) is characterized. High‐resolution X‐ray diffraction results show that the crystal quality of the film is improved compared with that of the template. Atomic force microscopy shows that the root mean square roughness value also decreases. Cathodoluminescence spectra show that the main impurities in the epitaxial layer and template are oxygen atoms. Raman spectroscopy and geometric phase analysis show that HVPE AlN samples maintain a compressive stress internally, which is the key to inhibit film cracking. Transmission electron microscope characterization reveals that most of the dislocations at the interface inherit from MOCVD AlN template, incline in the subsequent growth, react with each other, and finally annihilate. The dislocation bending and reduction mechanism are demonstrated.

Observation of threading dislocations and misfit dislocation half-loops in GaN/AlGaN heterostructures grown on Si using electron channeling contrast imaging

We implemented invisibility criterion and black–white contrast orientation analysis into low-tilt electron channeling contrast imaging (ECCI) for dislocation-type discrimination in GaN and AlGaN layers grown on a Si(111) substrate. Our ECCI and x-ray diffraction (XRD) analysis attained consistent threading dislocation densities for GaN and AlGaN grown on Si, but demonstrated drastic discrepancy in the percentage of edge-type dislocations, potentially due to the lack of appropriate consideration of mixed-type (a→+c→) dislocations in XRD. Further ECCI analysis of GaN/AlGaN heterointerface revealed mixed-type (a→+c→) dislocation half-loops and dislocation bending due to compressive strain relaxation, validating that not all the dislocations originated from the mosaic or columnar structure. As a result, XRD analysis based on the mosaic block model does not give reliable edge-to-screw dislocation ratio. The observation of classic van der Merwe–Matthews-type dislocation half-loop nucleation and dislocation gliding could be associated with potential GaN/AlGaN optoelectronic device degradation issues.

Study of Dislocation Bending During Film Growth by a Multiscale Scheme

AbstractDepositing on the patterned substrate in chemical vapor deposition is one of the most effective approaches to produce low‐dislocation‐density films. Existing experiments indicate that dislocation bending is the main cause of decreasing dislocation. However, what drives dislocation segments (DSs) to bend remains unclear, and existing numerical methods do not explain the mechanism fully. In this study, a multiscale scheme based on molecular dynamics (MD) and kinetic Monte Carlo (KMC) is proposed to unravel the multiscale mechanism of DSs bending. In this scheme, MD is employed to identify the off‐lattice structure and to calculate the diffusion activation energies. KMC is used to perform the temporal evolution of the deposition process. In a proof‐of‐concept, the growth rate and the film morphology in silane deposition are predicted in the cross‐scale comparable to the experimental measurements. With the proposed multiscale scheme, the calculated activation energies show that the repeated lateral deposition and the obliquely upward deposition of the dislocated atoms contribute to DSs bending. Moreover, the sharp decrease of dislocation density is quantitatively elucidated by the scheme. The study provides fundamental insight into dislocation bending reduction during crystal thin film growth.

Strengthening caused by precipitates with different morphologies in Cu–Cr–Ti alloys: The role of dislocation bending angle

Addition of a small amount of Ti can significantly improve strength of Cu–Cr alloys. Previous work found that addition of Ti produced both spherical and cubic-shaped Cr particles. In this work, the hindering effect of Cr particles with different morphologies on dislocation was further studied. Transmission electron microscopy and high-resolution transmission electron microscopy were used to observe the bending angle of dislocations cutting through precipitated phase particles at about 108° or 54°. The angle of dislocations cutting through the spherical particles was 108° and that of the cubic particles was 54°. Theoretical calculations of dislocation bending angle to enhance strength determined that the bending angle of dislocations cutting cubic particles is about 54°. This study provides new insights for the design and preparation of high-strength and high-conductivity copper alloys.

Sub- μ m features patterned with laser interference lithography for the epitaxial lateral overgrowth of α-Ga2O3 via mist chemical vapor deposition

The low growth rate of mist chemical vapor deposition normally requires a long growth time to achieve coalescence in the epitaxial lateral overgrowth of α-Ga2O3 thin films on sapphire substrates. To address this issue, sub-μm features were patterned using laser interference lithography. Periodical stripes with a ∼590-nm pitch allowed the overgrowth of crack-free, void-free, and continuous thin films, while typical growth conditions using a low carrier gas flow rate and a low Ga precursor concentration were maintained. Coalescence was achieved even with a short growth time of <30 min and a low film thickness of <500 nm. Transmittance and x-ray diffraction spectra show that the film was predominantly in α-phase. Transmission electron microscopy (TEM) images reveal cup-top-like α-Ga2O3 regions of low dislocation density on the SiOx mask. Selected area electron diffraction and high-resolution TEM analyses confirm that an α-Ga2O3 layer was formed even on the top of the SiOx mask. Interestingly, the dislocations formed on the window areas did not bend toward the center of the masks; rather, a dislocation bending outward from the center was observed. This suggests the occurrence of early coalescence and/or atomic rearrangement.

Numerical investigation on threading dislocation bending with InAs/GaAs quantum dots* *Project supported by the National Natural Science Foundation of China (Grant Nos. 61874148, 61974141, and 61674020), the Beijing Natural Science Foundation, China (Grant No. 4192043), the National Key Research and Development Program of China (Grant No. 2018YFB2200104), the Fund from the Beijing Municipal Science & Technology Commission, China (Grant No.

The threading dislocations (TDs) in GaAs/Si epitaxial layers due to the lattice mismatch seriously degrade the performance of the lasers grown on silicon. The insertion of InAs quantum dots (QDs) acting as dislocation filters is a pretty good alternative to solving this problem. In this paper, a finite element method (FEM) is proposed to calculate the critical condition for InAs/GaAs QDs bending TDs into interfacial misfit dislocations (MDs). Making a comparison of elastic strain energy between the two isolated systems, a reasonable result is obtained. The effect of the cap layer thickness and the base width of QDs on TD bending are studied, and the results show that the bending area ratio of single QD (the bending area divided by the area of the QD base) is evidently affected by the two factors. Moreover, we present a method to evaluate the bending capability of single-layer QDs and multi-layer QDs. For the QD with 24-nm base width and 5-nm cap layer thickness, taking the QD density of 1011 cm−2 into account, the bending area ratio of single-layer QDs (the area of bending TD divided by the area of QD layer) is about 38.71%. With inserting five-layer InAs QDs, the TD density decreases by 91.35%. The results offer the guidelines for designing the QD dislocation filters and provide an important step towards realizing the photonic integration circuits on silicon.

Reduction of dislocations in α-Ga2O3 epilayers grown by halide vapor-phase epitaxy on a conical frustum-patterned sapphire substrate.

The compound α-Ga2O3 is an ultra-wide-bandgap semiconductor and possesses outstanding properties such as a high breakdown voltage and symmetry compared with other phases. It has been studied for applications in high-performance power devices. However, it is difficult to obtain a high-quality thin films because α-Ga2O3 can only grow heteroepitaxially, which results in residual stress generation owing to lattice mismatch and thermal expansion between the substrate and α-Ga2O3. To overcome this, α-Ga2O3 was grown on a conical frustum-patterned sapphire substrate by halide vapor-phase epitaxy. The surface morphology was crack-free and flat. The α-Ga2O3 grown on a frustum-patterned substrate and a conventional sapphire substrate at 500°C exhibited full-width at half-maxima of 961 and 1539 arcsec, respectively, for 10-12 diffraction. For the former substrate, lateral growth on the pattern and threading dislocation bending towards the pattern suppressed the propagation of threading dislocations generated at the interface, which reduced the threading dislocation propagation to the surface by half compared with that on the latter conventional substrate. The results suggest that conical frustum-patterned sapphire substrates have the potential to produce high-quality α-Ga2O3 epilayers.

Microstructure and dislocation evolution in composition gradient AlGaN grown by MOCVD

In this study, the epitaxial growth of the full-composition-graded Al x Ga 1-x N films has been demonstrated on the sapphire substrates by using metalorganic chemical vapor deposition (MOCVD). The aluminum composition in the Al x Ga 1-x N films has been precisely controlled from 0 to 100%, as confirmed by X-ray diffraction and energy-dispersive spectroscopy analyses. The pseudo-periodic Al x Ga 1-x N/Al y Ga 1-y N structures are spontaneously formed during the initial growth of the graded AlGaN layer, which facilitate the strain relaxation. In addition, the behavior of the bending dislocations has been investigated in detail, and the threading dislocation bending along the growth direction is noted to relax the strain further. • We report the experimental full-composition graded Al x Ga 1-x N grown by MOCVD. • The pseudo-periodic structures with different intervals Al x Ga 1-x N layers and dislocation bending jointly regulate the relaxation of the compressively strained AlGaN layers. • The pseudo-periodic structures are composed of, which spontaneously formed during the initial growth stage of Al x Ga 1-x N.

Mathematical modeling of elastic wave radiation during infinite screw dislocation bending vibrations

In this paper, we consider elastic waves radiation (acoustic emission) by infinite screw dislocation performing small bending vibrations under action of external influences. Braking of the dislocation vibrations by medium was not taken into account. To solve this problem, inverse generalized susceptibility of an infinite screw dislocation is written down. It is found that condition for the emission of elastic waves by a screw dislocation is satisfied for two ranges of wave vector component values along the dislocation line. For average value of energy emitted per unit time per unit length of the screw dislocation, corresponding expressions are obtained. Internal friction caused by radiation losses during bending vibrations of the screw dislocation is found.

Effect of flux rate on AlN epilayers grown by hydride vapor phase epitaxy

The surface morphology and crystalline quality of AlN epilayers grown by high-temperature hydride vapor phase epitaxy (HVPE) with various growth rate were investigated by AFM, XRD and cross-sectional TEM analyses. The growth rate of AlN films were controlled by regulating the flux rates of HCl and NH3 while keeping V/III ratio constant. The surface morphology of as-grown AlN films revealed that the control of the appropriate growth rate is beneficial to obtain uniform step-flow morphology. And the crystalline quality of AlN layers has been improved at an appropriate growth rate, since the growth mode of AlN under such condition is beneficial to the bending of dislocations. The dislocation bending and reduction mechanism has also been demonstrated.

In-plane anisotropy in the direction of the dislocation bending in α-Ga2O3 grown by epitaxial lateral overgrowth

Threading dislocations in α-Ga2O3 grown by epitaxial lateral overgrowth (ELO) were observed by using atomic force microscopy after a surface etching using 10 wt% KOH aqueous solution heated at 60 °C. The ELO α-Ga2O3 was characterized by an in-plane anisotropy in the direction of the dislocation bending as followings: the dislocations in ELO α-Ga2O3 bend in the direction of α-Ga2O3, while the dislocation-free areas expand in the direction from the positions of windows. The anisotropy is an important factor to control the dislocations in α-Ga2O3 and to optimize the ELO of α-Ga2O3.

Numerical estimation of lattice strain, bending and generation of misfit dislocations in CdHgTe heterostructures grown on GaAs substrate

Using our own computer program, we determined the spatial distribution of lattice strains in the HgCdTe heterostructure grown on a GaAs substrate. Lattice stress resulting from lattice mismatch between the substrate and the epitaxial layer and bending of the heterostructure is almost completely relaxed by misfit dislocations forming matrixes in the interfaces’ areas. The average distances between dislocation lines in individual interfaces were calculated based on the minimum energy, i.e. elastic energy condition resulting from the interaction of stress fields and deformations caused by lattice misfit, bending and the presence of dislocation plus electrical energy of dislocations.

Quasi-Vertical GaN Schottky Barrier Diode on Silicon Substrate With 1010 High On/Off Current Ratio and Low Specific On-Resistance

In this letter, we report a quasi-vertical GaN Schottky barrier diode (SBD) fabricated on a hetero-epitaxial layer on silicon with low dislocation density and high carrier mobility. The reduction of dislocation is realized by inserting a thin layer with high density of Ga vacancies to promote the dislocation bending. The dislocation density is ${1.6}\times {10}^{{8}}$ cm−2 with a GaN drift layer thickness of $4.5~\mu \text{m}$ . The fabricated prototype GaN SBD delivers a high on/off current ratio of $10^{{10}}$ , a high forward current density of 1.6 kA/cm2@3 V, a low specific on-resistance of 1.1 $\text{m}\Omega \cdot \text {cm}^{{2}}$ , and a low ideality factor of 1.23.

Tailoring the potential landscape of room-temperature single-mode whispering gallery polariton condensate

A key point of exciton polaritons is real-time controllability of potential energy and its landscape due to the hybrid nature of excitons and photons. Although wide-bandgap semiconductors allow us to generate room-temperature polaritons, unintentional localizations of two-dimensional cavities caused by disorder (dephasing and potential fluctuation) still hinder the establishment of ballistic extensions of polariton condensates. This ballistic extension accompanies spatial coherence, an essential factor for phase transitions as well as any quantum controls. Here we propose a room-temperature polariton system with ultralow disorder capable of one-dimensional ballistic propagation. Selectively grown GaN wire dramatically reduces disorder in both the exciton perspective via dislocation bending and the photon perspective through crystallographically defined hexagonal cavities. This high-quality wire on a substrate forms triangular whispering gallery modes and allows us to demonstrate the room-temperature single-mode one-dimensional polariton condensate with ballistic propagation. This ballistic propagation is manipulated by active real-time control of the potential gradient. The correlation between propagation distances deduced from real and momentum space provides strong evidence of ballistic propagations in an ultralow-disordered one-dimensional system.