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Basal and prismatic slips induced by thermoelastic stresses during the growth of 4H-SiC are investigated by using the finite element method (FEM) and considering factors such as the crystal diameter, temperature, and off-axis angle. It is found that with the increase of the crystal diameter from 6 to 8 inches, the prismatic slip more likely occurs, leading to a higher density of basal plane dislocations (BPDs). However, the basal slip hardly changes. The temperature difference, rather than the growth temperature, is the primary factor contributing to the increase in the slip stresses. The stresses of the basal slip are significantly affected by a small off-axis angle, whereas those of the prismatic slip are not unaffected until the off-axis angle reaches 30 degrees. The mechanism for the decrease of the density of BPDs along the growth direction in an 8 inch 4H-SiC crystal is elucidated. We verify that the prismatic slip in an 8 inch 4H-SiC crystal contributes more to the BPD formation than the basal slip. [ABSTRACT FROM AUTHOR]

The primary challenge for preparing SiC crystals during the PVT process is the fractures, especially with the increase in diameter (≥8 inches). In this study, the elastic–plastic behaviors of the azimuthal component (σφφ) of primary stress causing SiC crystal fractures have been investigated to research the fracture mechanism. It is concluded that the plastic deformations caused by prismatic plane slips contribute positively to σφφ. Besides, the magnitude of the plastic component of σφφ is determined by the magnitude of resolved shear stresses (RSS) on each prismatic slip system over the same period, according to the Alexander–Haasen (AH) model. Further, the evolution of the magnitude of RSS (‖RSS‖) during the cooling process has been simulated, and the effects of the experimental conditions on the elastic–plastic behaviors of σφφ have been investigated qualitatively. Control experiments of SiC crystal growth have been carried out simultaneously, and our conclusions have been verified by the experimental results. Lastly, the maximum ‖RSS‖ can be a criterion for the fracture of SiC crystal, giving a critical value near 30 MPa under our experimental conditions. The analysis of the relation between the growth conditions and fractures guides the growth of perfect 8-inch SiC crystals. [ABSTRACT FROM AUTHOR]

Basal plane dislocations (BPDs) in 4H-SiC are the main reason for the degradation of bipolar devices. In the experiment, the distribution of 4-fold symmetry BPDs is observed in the etch pit density of the 4H-SiC wafer, which is inconsistent with the phenomenon of the distribution of 6-fold symmetry BPDs because of the hexagonal structure of 4H-SiC. To explain the distribution of 4-fold symmetry BPDs in the grown crystal, 3D modeling of BPDs in 4H-SiC crystals grown by the PVT method has been performed. The results show that the adoption of 4-degree off-axis seed crystals that are widely used in the industry caused the distribution of 4-fold symmetry BPDs. Moreover, the distribution of BPDs is 6-fold symmetry in on-axis grown 4H-SiC single crystals; with the increase of the off-angle, the distribution of BPDs gradually changes from 6-fold to 4-fold symmetry, and the maximum value of the BPD density is at the periphery. In the end, the strategy of growing 4H-SiC crystals with large-size seed crystals has been proposed to reduce the BPD density in the wafer and improve the quality of the substrate. The calculation results shows that the use of 220 mm seed crystals can reduce the BPD density by 15% compared with 200 mm seed crystals. [ABSTRACT FROM AUTHOR]

Top-seeded solution growth (TSSG) is a crucial technique for producing high-quality SiC crystals, with the quality of the crystal being significantly influenced by the temperature, flow, and carbon concentration in the solution. A global numerical simulation has been performed to investigate the effects of solution height and crystal rotation in SiC crystal growth. The simulation results indicate that as the solution height increases, there are two distinct flow patterns: single-vortex pattern and double-vortex pattern. Because of the change in the flow pattern, the flow field beneath the seed crystal and free surface will undergo a significant change. The varying effects of seed crystal rotation are also demonstrated under different solution height scenarios. Increasing the rotational speed of the seed crystal will enhance the stability of the solution flow field and crystal growth rate for the single-vortex pattern. Increasing the rotational speed or solution height appropriately is beneficial for enhancing the crystal growth rate in the double-vortex pattern. Excessively high rotational speeds or solution heights, however, will reduce the rate of crystal growth. [ABSTRACT FROM AUTHOR]

This paper focuses on the generation and transformation of defects associated with subsurface damages (SSDs) in seed crystals during the physical vapor transport (PVT) growth of 4H-SiC crystals. SSDs in the 4H-SiC seed crystal were first revealed and labeled through photo-chemical etching. After 30 min of PVT growth on the 4H-SiC seed crystal, we found that ridge-like substances with a height ranging from 0.2 to 1.5 μm were formed in the region above the SSDs in the 4H-SiC seed crystal. Raman spectra analysis indicated that these ridge-like substances were 4H-SiC under tensile strain. We then continued the PVT growth to obtain a 4H-SiC boule and carried out a wafering process to obtain 4H-SiC single-crystal wafers. For the bottom wafer, above the 4H-SiC seed wafer, the full width at a half maximum (FWHM) of the rocking curves of the region above the SSDs of the seed wafer was higher than that in the other regions, indicating that the SSDs degrade the crystalline quality of 4H-SiC single crystal. The average value of the FWHM of the rocking curves of the top wafer became lower than that of the bottom wafer, indicating that the effect of SSDs gradually recovers. Molten-KOH etching indicated that SSDs in the 4H-SiC seed crystal give rise to the formation of low-angular grain boundaries (LAGBs) that consist of a wall of threading edge dislocations (TEDs) in 4H-SiC single crystals. [ABSTRACT FROM AUTHOR]

A 4H-SiC single crystal is a substrate material for high-frequency and high-voltage power devices. Dislocation density is a fundamental criterion for evaluating the quality of 4H-SiC single crystals. 4H-SiC single crystals grown by the physical vapor transport (PVT) method generally have high dislocation density. To investigate the effect of nitrogen doping on dislocation proliferation in SiC crystals, the thermal field of the ingot during PVT growth was calculated by COMSOL Multiphysics, and thermal stress was calculated by thermal elastic theory. Finally, the dislocation density of the crystal was calculated based on the Alexander–Haasen model for inhomogeneous nitrogen doping. By comparing the calculation and experimental results, we proposed a possible value of the effective stress to evaluate the effect of a nitrogen dopant on dislocation density, which helps calculate the dislocation density in the n-type SiC. [ABSTRACT FROM AUTHOR]

We use silicon quantum dots (SiQDs) with an average diameter of 2.6 ± 0.5 nm as the light emitting material and fabricate inverted structure light emitting diodes (SiQD-LEDs) with bottom cathodes. ZnO nanoparticles with high electron mobility, a deep valence band edge, and robust features to resist dissolving by the SiQD solvent were used as the electron transport layer. 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC) with high hole transport mobility and a high lowest unoccupied molecular orbital level was used as the hole transport layer. Poly(ethylene imine) (PEI) modified indium-tin oxide (ITO) was used as the low work function (∼3.1 eV) cathode and MoO3/Al as the high work function anode. Electroluminescence of the SiQD-LEDs is mainly from the SiQDs with a peak located at ∼700 nm. The maximum external quantum efficiencies of the SiQD-LEDs are 2.7%. [ABSTRACT FROM AUTHOR]

When silicene is passivated by hydrogen, a bandgap occurs so that it becomes a semiconductor. Analogous to all the other semiconductors, doping is highly desired to realize the potential of hydrogen-passivated silicene (H-silicene). In the framework of density functional theory (DFT), we have studied the doping of H-silicene with boron (B) and phosphorus (P). The concentration of B or P ranges from 1.4% to 12.5%. It is found that the doping of B or P enables the indirect-bandgap H-silicene to be a semiconductor with a direct bandgap. With the increase of the concentration of B or P, both the valence band and the conduction band shift to lower energies, while the bandgap decreases. Both B- and P-doping lead to the decrease of the effective mass of holes and electrons in H-silicene. For both B- and P-doped H-silicene a subband absorption peak may appear, which blueshifts with the increase of the dopant concentration. [ABSTRACT FROM AUTHOR]

We demonstrate a facile method to prepare gelatin/Si nanocrystal composite thin films via a filtration technique using metal hydroxide nanostrands as a sacrificial layer. This film is free-standing and demonstrates fast and reversible detection of amines in water. [ABSTRACT FROM AUTHOR]

A free-standing fluorescent gelatin–Si nanoparticle composite thin film is facilely prepared by means of a filtration technique assisted by porous copper hydroxide nanostrands as a sacrificial layer. The as-prepared gelatin–Si nanoparticle composite film is greatly portable, flexible, transparent and free-standing. The most important advantage is its robust storage stability stored in ambient air, which make it promising for various applications. Meanwhile, a gelatin–Si–Au nanoparticle composite film is also successfully prepared by the formation of Au NPs in a gelatin–Si nanoparticle composite film through the in situ reduction of HAuCl4 at room temperature. The photoluminescence (PL) quenching and blue shift in the peak of the emission spectra occur due to the energy transfer from Si NPs to Au NPs. By varying the amount and size of Au NPs incorporated into the gelatin–Si nanoparticle composite film, the energy transfer efficiency can be controlled. This is a general method to prepare metal–semiconductor hybrid fluorescent nanomaterials, which offers the possibility of tuning the luminescence intensity and wavelength of the emitted light. [ABSTRACT FROM AUTHOR]

We propose a scheme utilizing the double plasmon modes of gold nanorods (GNRs) to efficiently increase the Förster resonant energy transfer (FRET) efficiency and enhance the photoluminescence (PL) of Si quantum dots (Si QDs) nearby. Detailed PL and decay dynamics studies are performed for the hybrid nanostructures composed of metallic nanoparticles (MNPs) coated with a Si QD-absorbed silica shell. Plasmon enhanced FRET between Si QDs has been observed and proposed as the third enhancement mechanism for the plasmon-enhanced photoluminescence in addition to excitation enhancement and emission enhancement mechanisms. A maximum FRET efficiency of 46.3% is obtained, which is enhanced by a factor of 8.7 compared to that of samples without MNPs. The dependence of the energy transfer efficiency and the enhancement of the acceptor emission on the surface plasmon resonance (SPR) wavelength, metal-QD distance and QD ratio is examined. The FRET enhancement mechanism dominates when the coupling of plasmon-donor is much stronger than that of plasmon-acceptor with a high acceptor/donor ratio., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Theoretical understanding of the surface modification of Cl-passivated silicon nanocrystals (Si NCs) is rather limited, in stark contrast to that for H-passivated Si NCs. We now investigate four surface-modification schemes (silanization, alkylation, alkoxylation and aminization) that have been experimentally adopted for Cl-passivated Si NCs in the framework of density functional theory. It is found that aminization most significantly affects the electronic structures of Si NCs by raising the highest occupied molecular orbital (HOMO). The effect of aminization depends on the substituents of amines, rather than the coverage of amine-derived ligands at the NC surface. The lowest unoccupied molecular orbital (LUMO) is more sensitive to the NC size than the HOMO. Only the HOMO is sensitive to surface modification. All the aminization leads to the decrease of the HOMO-LUMO gap despite that the dominant role of quantum confinement effect is maintained in most cases. The current results contribute to the understanding of the optical behavior of Si NCs derived from the surface modification of Cl-passivated ones.