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3D GaN Fins as a Versatile Platform for a-Plane-Based Devices
摘要： GaN fins on GaN-on-sapphire templates are fabricated by continuous mode selective area metalorganic vapor phase epitaxy. The fins exhibit high aspect ratios and smooth nonpolar a-plane sidewalls with an ultra-low threading dislocation density of a few 105 cm?2 making them ideally suited for optoelectronic to electronic applications. A detailed analysis of the inner structure of GaN fins is provided by the help of marker layer experiments and correlation of results from fins fabricated under different growth conditions, leading to the development of a growth model to explain the final geometry and optical as well as electrical properties of these high aspect ratio fins. Distinctly different material properties for the central and outer parts of the fins are detected. Whereas the outer sidewalls represent high quality GaN surfaces with very low defect densities, a strong quenching of near band edge emission (NBE) in the central part of the fins is accompanied by heavy compensation of free electrons. A possible explanation is the incorporation of excessive point defects, like intrinsic defects or carbon impurity. The sidewall regions, however, prove to be highly suitable for device applications due to their strong NBE emission, low dislocation density, and high free carrier concentration.
关键词： marker layers,threading dislocation density,GaN fins,selective-area MOVPE,a-plane sidewalls
更新于2025-09-23 15:22:29
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A discrete core-shell-like micro-light-emitting diode array grown on sapphire nano-membranes
摘要： A discrete core-shell-like micro-light-emitting diode (micro-LED) array was grown on a 100 nm-thick sapphire nano-membrane array without harmful plasma etching for chip singulation. Due to proper design for the sapphire nano-membrane array, an array of multi-faceted micro-LEDs with size of 4 μm × 16 μm was grown. threading dislocation density in the micro-LeD formed on sapphire nano-membrane was reduced by 59.6% due to the sapphire nano-membranes, which serve as compliant substrates, compared to GaN formed on a planar substrate. Enhancements in internal quantum efficiency by 44% and 3.3 times higher photoluminescence intensity were also observed from it. Cathodoluminescence emission at 435 nm was measured from c-plane multiple quantum wells (MQWs), whereas negligible emissions were detected from semi-polar sidewall facets. A core-shell-like MQWs were formed on all facets, hopefully lowering concentration of non-radiative surface recombination centers and reducing leakage current paths. This study provides an attractive platform for micro-LEDs by using sapphire nano-membrane.
关键词： internal quantum efficiency,photoluminescence,threading dislocation density,micro-LED,sapphire nano-membrane,core-shell-like,cathodoluminescence
更新于2025-09-23 15:21:01
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Numerical Modelling on Modified Directional Solidification Process of Multi-crystalline Silicon Growth for Photovoltaic Applications
摘要： A transient global model was used to investigate the effect of bottom grooved furnace upon the directional solidification (DS) process of multi-crystalline silicon (mc-Si). The numerical simulation assumed geometry is perfect 2D axis-symmetry. The temperature distribution, crystal-melt (c-m) interface, thermal stress and dislocation density have been simulated. The modified heat exchanger block system was used for controlling the temperature gradient at the bottom of the crucible. The obtained result shows convex shape of the c-m interface. The von Mises stress and dislocation density were reduced while using the bottom grooved furnace. This work was carried out in the different grooves of radius 30 and 60 mm of the heat exchanger block of the DS furnace.
关键词： Directional solidification,Dislocation density,Thermal stress,Silicon,Solar cells,Numerical simulation
更新于2025-09-16 10:30:52
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Dislocation density-based study of grain refinement induced by laser shock peening
摘要： Laser shock peening (LSP) is an innovative surface processing technique. Grain re?nement induced by LSP has been proved to be feasible to improve the surface properties of materials and prolong the service life of metallic components. The three-dimensional ?nite element model, which incorporates a dislocation density-based constitutive model and the temporal-spatial distribution of laser shock wave, was adopted to simulate the process of grain re?nement induced by LSP. The predicted dislocation cell sizes, dimple fabrications induced by the repetitive LSP of copper are in good agreement with experimental results, which con?rms the validity of the dislocation density-based three-dimensional ?nite element model. The e?ects of laser spot overlap ratio and laser power density (peak laser shock wave pressure) on LSP-induced grain re?nement were investigated in detail based on the numerical simulations of multiple LSP of copper and CP-Ti.
关键词： Laser shock peening,Dislocation density evolution,Cell size,Grain re?nement
更新于2025-09-11 14:15:04
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Structural, vibrational, Hirshfeld surfaces and optical studies of nonlinear optical organic imidazolium L-tartrate single crystal
摘要： Imidazolium L-tartrate (IMLT) single crystal was grown using solution growth technique. The grown crystal belongs to monoclinic crystal structure with space group P21. Intermolecular interactions of IMLT is executed by the Hirshfeld surface analysis. The structure of the grown crystal was stabilized by an extensive network of O–H···O, N–H···O and O–H hydrogen bonds. The vibrational modes are assigned based on potential energy distribution (PED). 13C and 1H NMR spectra were recorded to interpret the environment of the molecular structure. The HOMO-LUMO energy gap shows that the molecular chemical stability is high for the IMLT molecule. The Mulliken charge distribution confirms that the highest value is noted in C17, whereas the lowest value is obtained in C10 atom. The natural bond orbital (NBO) analysis has been computed to find out the electron delocalization and conjugative interactions. The bonding and anti-bonding orbitals are performed using density of states (DOS) spectrum. From photoconductivity measurement, the dark current is seen to be less than photocurrent. The etching analysis was done on (0 0 1) plane of IMLT crystal and rectangular etch pits are observed.
关键词： ICT,Dislocation density,Photosensitivity,OPDOS,Hirshfeld surfaces
更新于2025-09-10 09:29:36
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Defects and their reduction in Ge selective epitaxy and coalescence layer on Si with semicylindrical voids on SiO<formula><tex>$_{2}$</tex></formula> masks
摘要： Formation of semicylindrical voids on SiO2 masks in Ge layers selectively grown on Si has positive impacts for reduction of threading dislocation density (TDD). Semicylindrical voids are formed through selective epitaxial growth (SEG) and coalescence of SEG Ge layers. A cross-sectional transmission electron microscope (TEM) observation reveals that a threading dislocation (TD) is terminated at a semicylindrical void, resulting in the reduction of TDD. The semicylindrical voids also contribute to the suppression of two-dimensional defects generated at the coalesced interfaces between the SEG Ge layers, which were widely observed in previous reports. Plan-view TEM observations reveal that there are TDs inclined to be parallel to the semicylindrical voids, and plan-view TEM observations show a large (4 μm × 4 μm) TD-free area in the Ge layer with the semicylindrical voids.
关键词： silicon photonics,threading dislocation density,germanium (Ge),semiconductor epitaxial layers,Epitaxial growth
更新于2025-09-10 09:29:36
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Molecular Dynamics Simulation on B3-GaN Thin Films under Nanoindentation
摘要： The B3-GaN thin film was investigated by performing large-scale molecular dynamics (MD) simulation of nanoindentation. Its plastic behavior and the corresponding mechanism were studied. Based on the analysis on indentation curve, dislocation density, and orientation dependence, it was found that the indentation depths of inceptive plasticity on (001), (110), and (111) planes were consistent with the Schmid law. The microstructure evolutions during the nanoindentation under different conditions were focused, and two formation mechanisms of prismatic loop were proposed. The “lasso”-like mechanism was similar to that in the previous research, where a shear loop can translate into a prismatic loop by cross-slip; and the extended “lasso”-like mechanism was not found to be reported. Our simulation showed that the two screw components of a shear loop will glide on another loop until they encounter each other and eventually produce a prismatic dislocation loop.
关键词： anisotropy,dislocation density,prismatic loops,B3-GaN,molecular dynamics
更新于2025-09-09 09:28:46