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Si-based group III-V material enables a multitude of applications and functionalities of the novel optoelectronic integration chips (OEICs) owing to their excellent optoelectronic properties and compatibility with the mature Si CMOS process technology. To achieve high performance OEICs, the crystal quality of the group III-V epitaxial layer plays an extremely vital role. However, there are several challenges for high quality group III-V material growth on Si, such as a large lattice mismatch, highly thermal expansion coefficient difference, and huge dissimilarity between group III-V material and Si, which inevitably leads to the formation of high threading dislocation densities (TDDs) and anti-phase boundaries (APBs). In view of the above-mentioned growth problems, this review details the defects formation and defects suppression methods to grow III-V materials on Si substrate (such as GaAs and InP), so as to give readers a full understanding on the group III-V hetero-epitaxial growth on Si substrates. Based on the previous literature investigation, two main concepts (global growth and selective epitaxial growth (SEG)) were proposed. Besides, we highlight the advanced technologies, such as the miscut substrate, multi-type buffer layer, strain superlattice (SLs), and epitaxial lateral overgrowth (ELO), to decrease the TDDs and APBs. To achieve high performance OEICs, the growth strategy and development trend for group III-V material on Si platform were also emphasized.

The fabrication of high‐speed electronic and communication devices has rapidly grown the demand for high mobility semiconductors. However, their high cost and complex fabrication process make them less attractive for the consumer market and industrial applications. Indium nitride (InN) can be a potential candidate to fulfill industrial requirements due to simple and low‐cost fabrication process as well as unique electronic properties such as narrow direct bandgap and high electron mobility. In this work, 3 µm thick InN epilayer is grown on (0001) gallium nitride (GaN)/Sapphire template under In‐rich conditions with different In/N flux ratios by molecular beam epitaxy. The sharp InN/GaN interface monolayers with the In‐polar growth are observed, which assure the precise control of the growth parameters. The directly probed electron mobility of 3610 cm2 V‐1 s‐1 is measured with an unintentionally doped electron density of 2.24 × 1017 cm‐3. The screw dislocation and edge dislocation densities are calculated to be 2.56 × 108 and 0.92 × 1010 cm‐2, respectively. The step‐flow growth with the average surface roughness of 0.23 nm for 1 × 1 µm2 is confirmed. The high quality and high mobility InN film make it a potential candidate for high‐speed electronic/optoelectronic devices. High electron mobility is achieved by reducing the dislocation density and unintentional electron doping by boundary temperature controlled epitaxy method under indium‐rich growth conditions. The method can be applied for industrial‐scale production of InN for commercial optoelectronic device applications.

The analysis of line broadening in X-ray and neutron diffraction patterns using profile functions constructed on the basis of well-established physical principles and TEM observations of lattice defects has proven to be a powerful tool for characterizing microstructures in crystalline materials. These principles are applied in the convolutional multiple-whole-profile (CMWP) procedure to determine dislocation densities, crystallite size, stacking fault and twin boundary densities, and intergranular strains. The different lattice defect contributions to line broadening are separated by considering the hkl dependence of strain anisotropy, planar defect broadening and peak shifts, and the defect dependent profile shapes. The Levenberg–Marquardt (LM) peak fitting procedure can be used successfully to determine crystal defect types and densities as long as the diffraction patterns are relatively simple. However, in more complicated cases like hexagonal materials or multiple-phase patterns, using the LM procedure alone may cause uncertainties. Here, we extended the CMWP procedure by including a Monte Carlo statistical method where the LM and a Monte Carlo algorithm were combined in an alternating manner. The updated CMWP procedure eliminated uncertainties and provided global optimized parameters of the microstructure in good correlation with electron microscopy methods.

In this work, we present a finite deformation, fully coupled thermomechanical crystal plasticity framework. The model includes temperature dependence in the kinematic formulation, constitutive law and governing equilibrium equations. For demonstration, we employ the model to study the evolution and formation of residual stresses, residual statistically stored dislocation density and residual lattice rotation due solely to solid state thermal cycling. The calculations reveal the development of microplasticity within the microstructure provided that the temperature change in the thermal cycle is sufficiently large. They also show, for the first time, that the thermal cycling generates an internally evolving strain rate, where the contributions of mechanical strain and plasticity depend on temperature change. The calculations suggest a strong connection between the maximum temperature of a given cycle and the magnitude of the residual stresses generated after the cycle. A pronounced influence of elastic anisotropy on the heterogeneity of the residual stress distribution is also demonstrated here. Finally, we calculate lattice rotation obtained from thermal cycling ranging from ± 0 . 4 ∘ and show the relation between changes in predominant slip systems with short range intragranular lattice rotation gradients. The model can benefit metal process design, especially where large strains and/or large temperature changes are involved, such as bulk forming and additive manufacturing.

Wedge indentation experiments were conducted to study the depth dependence of geometrically necessary dislocation (GND) structures in single-crystalline tungsten. Single-crystalline tungsten exhibits a pronounced indentation size effect (ISE), which can be rationalized based on GNDs. The dislocation mechanisms, however, are still under debate. Due to the plane strain condition during the wedge indentation, the dislocations in the cross sections underneath indents could be analyzed based on the Nye tensor and the lattice rotations determined using transmission Kikuchi diffraction. The dislocation structures depend on the size of the indent confirming the different hardness regimes and the bilinear ISE reported recently. For shallow indents, the dislocations are rather localized at the tip of the indent, while with increasing depth the dislocation volume expands; subgrains and distinct rays of increased dislocation density form. At larger depths, the indentation-induced deformation fields exhibit characteristics similar to the kink-type shear at a stationary crack tip. Graphical abstract

Atomistic molecular dynamics (MD) and a microstructural dislocation density-based crystalline plasticity (DCP) framework were used together across time scales varying from picoseconds to nanoseconds and length scales spanning from angstroms to micrometers to model a buried copper–nickel interface subjected to high strain rates. The nucleation and evolution of defects, such as dislocations and stacking faults, as well as large inelastic strain accumulations and wave-induced stress reflections were physically represented in both approaches. Both methods showed similar qualitative behavior, such as defects originating along the impactor edges, a dominance of Shockley partial dislocations, and non-continuous dislocation distributions across the buried interface. The favorable comparison between methods justifies assumptions used in both, to model phenomena, such as the nucleation and interactions of single defects and partials with reflected tensile waves, based on MD predictions, which are consistent with the evolution of perfect and partial dislocation densities as predicted by DCP. This substantiates how the nanoscale as modeled by MD is representative of microstructural behavior as modeled by DCP.

A patterned Si substrate is used to reduce the threading dislocation density (TDD) in a Ge epitaxial film for near-infrared photonic device applications. Using photolithography and dry etching, an array of submicron-wide strips with a rectangular cross-section is patterned in the [110] direction of a Si (001) wafer. A Ge film as thick as 1 µm is grown on the patterned Si by chemical vapor deposition with an ordinary two-step growth method, where a buffer layer of pure Ge as thin as 50 nm is grown at a low temperature of 370°C, followed by growth at an elevated temperature of 700°C. A Ge film is formed with a reasonably flat surface despite the non-flat starting Si surface as well as the large lattice mismatch of 4.2% between Ge and Si. The etch-pit density measurements for the Ge film exhibits TDD of about 6 × 107 cm–2, which is significantly lower than that of about 2 × 108 cm–2 for the film on the unpatterned region prepared on the same Si substrate. The TDD reduction is attributed to a trapping of the dislocations in the trench regions between the Si strips, as observed in cross-sectional transmission electron microscope images.

Directed energy deposition with laser beam (DED-LB) components experience significant residual stress due to rapid heating and cooling cycles. Excessive residual tensile stress can lead to cracking in the deposited sample, resulting in service failure. This study utilized digital image correlation (DIC) and thermal imaging to observe the in situ temporal evolution of strain and temperature gradients across all layers of a deposited 316 L stainless steel thin wall during DED-LB. Both continuous-wave (CW) and pulsed-wave (PW) laser modes were employed. Additionally, the characteristics of thermal cracks and geometric dislocation density were examined. The results reveal that PW mode generates a lower temperature gradient, which in turn reduces thermal strain. In CW mode, the temperature–stress relationship curve of the additive manufacturing sample enters the “brittleness temperature zone”, leading to the formation of numerous hot cracks. In contrast, PW mode samples are almost free of cracks, as the metal avoids crack-sensitive regions during solidification, thereby minimizing hot crack formation. Overall, these factors collectively contribute to reduced residual stress and improved mechanical properties through the adjustment of pulsed-wave laser deposition.

Shot peening (SP) is a widely used surface treatment technology of metallic materials. In order to investigate the effects of the shot velocity and the SP coverage on the surface integrity of the SPed materials, a numerical prediction framework combining the finite element method (FEM) with the artificial neural network (ANN) algorithm was proposed. A three-dimensional finite element model in conjunction with the dislocation density-based constitutive relation was developed to simulate the process of SP of 42CrMo steel. The FEM was validated by comparing the prediction results with the experimental data including the indentation profile produced by the single-shot impact and the in-depth residual stresses induced by the multiple-shot impacts. Based on the FEM simulation results, an attempt to predict the surface integrity of 42CrMo steel subjected to SP was made by taking advantage of the ANN algorithm, and the obtained results indicate that the predictions of the GA-BP-ANN algorithm (the back-propagation artificial neural network algorithm optimized by the genetic algorithm) are in good agreement with the FEM simulation results in terms of the SP-induced residual stresses, equivalent plastic strain, grain refinement, and surface roughness. This study therefore provides a new idea to predict the surface integrity of the metallic materials subjected to SP by combining the FEM simulation with ANN algorithm.

Shot peening (SP) and surface mechanical attrition treatment (SMAT) are two well-known metal surface strengthening treatment techniques aimed at improving the service life of mechanical components. The residual stresses, grain refinement, and surface roughness are three important results of SP and SMAT. The compressive residual stresses are usually considered as the macroscopic strengthening mechanism, and grain refinement is the microscopic strengthening mechanism, while surface roughness is a disadvantage factor affecting the metallic surface integrity. For comprehensively comparative study of grain refinement, residual stresses, and surface roughness resulted from SP and SMAT, two types of three-dimensional parametric finite element models were respectively developed to simulate the processes of SP and SMAT, and the dislocation density–based material constitutive model was used for the numerical computations. Firstly, based on the simulation results of single and repetitive shot impacts, the effects of plastic strain rate, repetitive shot impact number, and shot incidence angle on grain refinement, dimple depth, and dynamic stress evolution were investigated in detail. The processes of multiple shot impacts were then simulated by the method of step-by-step parallel computation of multi-models, and the comparative study of SP and SMAT was carried out accordingly. Lastly, the surface grain refinement process with respect to SMAT coverage was further discussed, and a piecewise function was proposed to characterize the process, which could provide effective guidance for the industrial application of SMAT technique.