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Silicon carbide (SiC) has large refractive index, wide bandgap, and strong material-based second- and third-order nonlinearities. Thus, in recent years, SiC has attracted considerable interests in quantum and nonlinear integrated photonics [1] – [3] with potential applications within broadband nonlinear light sources, including photon-pair sources, supercontinuum generation, and frequency combs. Optical parametric oscillation (OPO) is regarded as a promising way to produce new frequencies and an important tool in generation of coherent light sources, such as frequency combs. In this work, we experimentally demonstrate a Kerr-nonlinearity based dual continuous-wave(CW) pumped OPO in a 4H-SiC-on-insulator (4H-SiCOI) microring resonator.

Contribution to conference. Abstract from the 47thMicro and Nano Engineering Conference 2021, Turin,20/09/2021-23/09/2021.

This study investigated the fabrication of porous fluorescent SiC using a constant voltage-controlled anodic oxidation process. The application of a high, constant voltage resulted in a spatial distinction between the porous structures formed inside the fluorescent SiC substrates, due to the different etching rates at the terrace and the large step bunches. Large, dendritic porous structures were formed as the etching process continued and the porous layer thickened. Under the conditions of low hydrofluoric acid (HF) concentration, the uniformity of the dendritic porous structures through the entire porous layer was considerably improved compared with the conditions of high HF concentration. The resulting large uniform structure offered a sizable surface area, and promoted the penetration of atomic layer-deposited (ALD) Al2O3 films (ALD&ndash, Al2O3). The emission intensity in the porous fluorescent SiC was confirmed via photoluminescence (PL) measurements to be significantly improved by a factor of 128 after ALD passivation. With surface passivation, there was a clear blueshift in the emission wavelength, owing to the effective suppression of the non-radiative recombination rate in the porous structures. Furthermore, the spatial uniformity of emitted light was examined via PL mapping using three different excitation lasers, which resulted in the observation of uniform and distinctive emissions in the fluorescent SiC bulk and porous areas.

Deploying wireless objects or devices is a fundamental basis for many network-based applications. The objects could be smart meters in a smart gird, sensors or actuators in a WSN, or IoT things. After the physical deployment of those devices, a network address allocation becomes another essential procedure to enable network communications among the devices for device controls or message delivery purposes. This paper gives a review on several notable address assignment mechanisms by describing the key technique of each of these proposed approaches. The advantages as well as weaknesses are also introduced and a brief comparison is also given in this paper. The review provides a valuable reference in making further improvement of distributed address allocations and a meaningful reference for the relevant applications in the topics of smart grid, sensor networks, and Internet of things.

The excitation power and temperature dependences of photoluminescence (PL) emission in 6H polytype of silicon carbide are investigated extensively. A sublinear power-function dependence of the donor-acceptor pair emission intensity on the excitation power is explained by a rate-equation model. A very low power exponent $(k=0.3)$ in a power-law dependence of PL intensity on the excitation power of $\mathrm{B}$-$\mathrm{N}$ codoped 6H-$\mathrm{Si}\mathrm{C}$ at room temperature indicates that three-particle Auger recombination is the main carrier recombination pathway. Auger recombination in an $\mathrm{Al}$-$\mathrm{N}$ codoped $\mathrm{Si}\mathrm{C}$ does not manifest as strongly as that of the $\mathrm{B}$-$\mathrm{N}$ codoped sample due to high density of ionized impurities which capture the nonequilibrium carriers faster. The ionized impurities form localized potential wells due to their random distribution, which is revealed by a blue shift of the PL band with increasing excitation intensity (approximately 16 meV per decade) and with decreasing temperature. Low-temperature Hall-effect measurement of the $\mathrm{Al}$-$\mathrm{N}$ codoped sample confirms the high density of ionized impurities and significantly reduced ionization energy of dopant states by approximately 53 meV due to the high dopant densities. These results could lead to realization of tunable $\mathrm{Si}\mathrm{C}$-based light sources in severe operating conditions.

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We investigated the effects of different growth facets of 6H-SiC and different voltage waveforms on the porous structure and luminescence properties. The structure formed on the surface after anodic etching significantly changed because of the difference in the growth plane, whereas dendritic and columnar pores were observed inside the Si- and C-face samples. These large porous structures were shown to promote the penetration depth of the atomic-layer-deposited Al2O3 films, and a recorded passivation depth of 30 μm layer was confirmed in C-face porous SiC. From the results using a fluorescence microscope and photoluminescence spectra measurement, it was concluded that the pulsed-voltage etching was preferable for fabricating uniform porous structures compared with the constant-voltage etching. However, the enhancement of the luminescence intensity needs to be further improved to realize high luminescent efficiency in porous fluorescent SiC.

We propose a silicon strip waveguide structure with alumina thin-film coating in-between the core and the cladding for group-velocity dispersion tailoring. By carefully designing the core dimension and the coating thickness, a spectrally-flattened near-zero anomalous group-velocity dispersion within the telecom spectral range is obtained, which is predicted to significantly broaden the bandwidth of four-wave mixing. We validate this by characterizing the wavelength conversion in a waveguide sample by atomic layer deposition technology, which to our best knowledge is the first experimental demonstration of the proposed structure. Due to the alumina thin-film coating, the wavelength conversion bandwidth reaches $58\sim\mathrm{nm}$, an increase by a factor of 1.3 compared to the corresponding structure without coating. This method can also be applied to other material platforms and applications requiring accurate group-velocity dispersion control.

AbstarctWe report for the first time a NUV light to white light conversion in a N-B co-doped 6H-SiC (fluorescent SiC) layer containing a hybrid structure. The surface of fluorescent SiC sample contains porous structures fabricated by anodic oxidation method. After passivation by 20 nm thick Al2O3, the photoluminescence intensity from the porous layer was significant enhanced by a factor of more than 12. Using a porous layer of moderate thickness (~10 µm), high-quality white light emission was realized by combining the independent emissions of blue-green emission from the porous layer and yellow emission from the bulk fluorescent SiC layer. A high color rendering index of 81.1 has been achieved. Photoluminescence spectra in porous layers fabricated in both commercial n-type and lab grown N-B co-doped 6H-SiC show two emission peaks centered approximately at 460 nm and 530 nm. Such blue-green emission phenomenon can be attributed to neutral oxygen vacancies and interface C-related surface defects generated dring anodic oxidation process. Porous fluorescent SiC can offer a great flexibility in color rendering by changing the thickness of porous layer and bulk fluorescent layer. Such a novel approach opens a new perspective for the development of high performance and rare-earth element free white light emitting materials.

As a promising new class of near-infrared light emitters, GaAsBi laser diodes (LDs) are considered to have a high energy efficiency and an insensitive temperature dependence of the band gap. In this paper, we realize the longest ever reported lasing wavelength up to 1.142 μm at room temperature in GaAsBi0.058/GaAs quantum well LDs grown by molecular beam epitaxy. The output power is up to 127 mW at 300 K under pulsed mode. We also demonstrate continuous wave mode operation up to 273 K for the first time. The temperature coefficient of the GaAsBi/GaAs LD is 0.26 nm/K in the temperature range of 77–350 K, lower than that of both InGaAsP/InP and InGaAs/GaAs LDs. The characteristic temperature is extracted to be 139 K in the temperature range of 77–225 K and decreases to 79 K at 225–350 K.

Silver (Ag) nanoparticles (NPs) were deposited on the surface of bulk Nitrogen-Boron co-doped 6H silicon carbide (SiC), and the Ag NPs were observed to induce localized surface plasmons (LSP) resonances on the SiC substrate, which was expected to improve the internal quantum efficiency (IQE) of the emissions of the donor-acceptor pairs of the SiC substrate. Room-temperature measurements of photoluminescence (PL), transmittance and time-resolved photoluminescence (TRPL) were applied to characterize the LSP resonances. Through the finite-difference time-domain (FDTD) simulation of the LSP resonance of an Ag nanoparticle on the SiC substrate, it is predicted that when the diameter of the cross section on the xy plane of the Ag nanoparticle is greater than 225 nm, the LSP starts to enhance the PL intensity. With implementation of a 3rd order exponential decay fitting model to the TRPL results, it is found that the average minority carrier lifetime of the SiC substrate decreased.

In this letter, an improved domain decomposition (DD) finite-difference time-domain (FDTD) method based on the weighted Laguerre polynomials (WLPs) is proposed to simulate far-field super-resolution focusing of time reversal (TR) waves. The unconditionally stable WLP-FDTD method is very suitable for solving this multiscale problem involving special microstructures in a subwavelength array. The derived higher order perfectly matched layer with auxiliary differential equations can be placed very close to walls, and thus the simulation area can be reduced accordingly. Moreover, the reverse Cuthill–Mckee scheme for matrix bandwidth compression is employed to improve the efficiency of DD-WLP-FDTD. A numerical example of TR wave propagation is included to validate the accuracy and efficiency of the improved method.

In this paper, an efficient domain decomposition (DD) technique is originally introduced into the unconditionally stable Crank–Nicolson finite-difference time-domain (CN-FDTD) method for analyzing the extraordinary optical transmission (EOT) phenomenon of periodic metallic gratings. Being caused by the evanescent waves propagating along the metal-dielectric interface in the visible and near infrared regions, the dispersion of the considered metal in this case is expressed by the Drude model and solved with a generalized auxiliary differential equation (ADE) technique. The periodic boundary condition is applied to the two-dimensional periodic metallic grating structures due to their periodicity. Then, the standard unsplit-field perfectly matched layer is derived as the absorbing boundary condition for CN-FDTD based on the ADE concept. In DD structures, the whole computational domain is divided into several subdomains to reduce the matrix size and save calculating time. Furthermore, the reverse Cuthill–Mckee scheme for the lower–upper decomposition is applied to the subdomain matrices individually to improve the efficiency of DD-CN-FDTD. Finally, two numerical examples are calculated and the physical mechanism of the EOT phenomenon is investigated. The results from the proposed method demonstrate its accuracy and efficiency for the nanostructures.

In this paper, the Newmark-Beta algorithm is introduced into the finite-difference time-domain (FDTD) method in dispersion media, resulting in an unconditionally stable method for periodic metallic grating analysis. The proposed method eliminates the Courant-Friedrich-Levy constraint and improves the simulation efficiency for multiscale problems. The dispersion of the metal, which is caused by the evanescent waves propagating along the interface between the metal and dielectric materials in the visible and near-infrared regions, is solved with a generalized auxiliary differential equation (ADE) technique. The extraordinary optical transmission through a periodic metallic grating with different number and different size of the perpendicular bump is also investigated. Compared with the traditional ADE-FDTD method and ADE alternating-direction-implicit FDTD method, the results from the proposed method show its accuracy and efficiency.

We demonstrate enhanced four-wave mixing (FWM) in high-quality factor, high-confinement 4H-SiC microring resonators via continuous-wave FWM. With the large power buildup effect of the microring resonator, −21.7 dBFWM conversion efficiency is achieved with 79 mW pump power. Thanks to the strong light confinement in SiC-on-insulator (SiCOI) waveguides with submicrometer cross-sectional dimensions, a high nonlinear parameter wγ of 7.4±0.9 W−1 m−1 is obtained, from which the nonlinear refractive index (n2) of 4H-SiC is estimated to be (6.0±0.6)×10−19 m2/W at the telecom wavelengths. Besides, we are able to engineer the dispersion of a SiCOI waveguide to achieve 3 dB FWM conversion bandwidth of more than 130 nm. This work represents a step toward enabling all-optical signal processing functionalities using highly nonlinear SiCOI waveguides.

We experimentally demonstrate a photon-pair source, based on continuous-wave pumped spontaneous four-wave mixing in a silicon microring resonator, which efficiently generates photon pairs with high coincidence counts, high brightness, and high coincidence-to-accidental ratio at multiple resonance wavelengths matching a standard International Telecommunication Union (ITU) frequency grid. The signal-idler joint spectral intensity is measured with a very high resolution of 2pm over multiple wavelengths by an optical spectrum analyzer through probe-swept stimulated four-wave mixing, allowing an accurate quantification of the spectral correlation. Strong spectral correlation and uniform degree of quantum correlation are observed from the source, and the measured amount of spectral modes agrees well with that obtained by unheralded second-order correlation measurements.

High concentrations of aluminum (Al) and nitrogen (N) dopants of 6H SiC have been achieved by a fast sublimation growth process. The Al–N co-doped 6H-SiC layer exhibits a strong light-blue photoluminescence emission at low temperatures due to emissions from DI centers and donor acceptor pairs (DAP). The photoluminescence quenching mechanisms of those emissions are different. The decrease of free carrier capture cross-section as temperature increases according to the cascade capture process causes quenching of the photoluminescence emission form DI centers. Emission from Al–N DAP centers exhibits an exponential quenching with activation energy of (95 ± 10) meV. This is attributed to a competing hole capture by non-radiative defect in a multiphonon emission process.

Silicon carbide (SiC) exhibits promising material properties for nonlinear integrated optics. We report on a SiC-on-insulator platform based on crystalline 4H-SiC and demonstrate high-confinement SiC microring resonators with sub-micron waveguide cross-sectional dimensions. The Q factor of SiC microring resonators in such a sub-micron waveguide dimension is improved by a factor of six after surface roughness reduction by applying a wet oxidation process. We achieve a high Q factor (73,000) for such devices and show engineerable dispersion from normal to anomalous dispersion by controlling the waveguide cross-sectional dimension, which paves the way toward nonlinear applications in SiC microring resonators.

The excitation-dependent photoluminescence quantum yield (PL-QY) of strong n-type nitrogen-boron codoped 6H fluorescent silicon carbide (f-SiC) at room temperature is experimentally determined for the first time. The PL-QY measurements are realized by an integrating sphere system based on a classical two-measurement approach. In particular, in accordance to the difference between our in-lab setup and the standard setup of the two-measurement approach, we have technically modified the experimental design, the data processing algorithm, and the estimation of relative uncertainty. The measured highest PL-QY of f-SiC samples is found to reach above 30%. We compare the PL-QYs at a certain excitation power of all f-SiC samples by considering their intrinsic defect densities. Finally, the evolution of the excitation power-dependent PL-QY of f-SiC is attributed to both band-to-band and impurity-assisted Auger recombination.

A new boron-induced deeper acceptor level (D*-center) different from the D-center in nitrogen-boron co-doped 6H fluorescent silicon carbide (f-SiC) is revealed by measuring the temperature-dependent photoluminescence (PL). The D*-center is correlated to the dominate donor-acceptor-pair (DAP) recombination at low temperature ranges in f-SiC with a PL peak around 1.90 eV. A hole-trap with an energy level that lies between the D*-center and the D-center is predicted to exist in the f-SiC samples. A two-step thermal ionization involving the hole-trap is proposed to explain the evolution of both D*-center and D-center related temperature-dependent DAP recombination.

We generate correlated photon pairs in an all-pass silicon microring resonator using continuous-wave pumped spontaneous four-wave mixing and we characterize in detail the optical bistability in the non-classical single-photon regime. Special attention is given to the resonance-locked method by balancing the pump-induced heating and the active off-chip cooling, leading to stable operation of the photon-pair source. The maximal coincidence rate of 20.53 ± 0.34 Hz, maximal coincidence-to-accidental ratio of 654 ± 125, and minimal zero-delayed heralded second-order correlation of 0.14 ± 0.09 are achieved. The wavelengths of photon pairs remain unchanged at different pump power, indicating that our source is more compatible with the common communication systems than those using conventional on-resonance strategies, that tunes the pump wavelength. This work not only experimentally validates the nonclassical bistability behaviors, but also puts forward a simple method of pump-resonance matching for high-quality performance.

An intense and broadband photoluminescence emission is demonstrated in a bio-compatible film produced by thermal annealing of poly(acrylic acid) (PAA). The annealing process enhances the emission intensity from weakly emitting sub-luminophores of C–O and C=O functional groups by a factor of more than two orders of magnitude. The emission property can be sensitively tuned by the annealing temperature, duration, the PAA solution preparation conditions such as solvent type and solvent:PAA ratio. The strong luminescence is attributed to the formation of rigid molecular structure due to aggregation and crosslinking. FTIR measurements show that the aggregation and crosslinking processes subdue nonradiative recombination pathways.

A higher-order PML is proposed for the WLP-FDTD method.The parameter values in the higher-order PML are optimized by MOGA.The higher-order PML is efficient in terms of absorbing performance.The WLP-FDTD method is employed to analyze the TR wave propagation problem. Derived from a stretched coordinate formulation, a higher-order complex frequency shifted (CFS) perfectly matched layer (PML) is proposed for the unconditionally stable finite-difference time-domain (FDTD) method based on weighted Laguerre polynomials (WLPs). The higher-order PML is implemented with an auxiliary differential equation (ADE) approach. In order to further improve absorbing performance, the parameter values of stretching functions in the higher-order PML are optimized by the multi-objective genetic algorithm (MOGA). The optimal solutions can be chosen from the Pareto front for trading-off between two independent objectives. It is shown in a numerical test that the higher-order PML is efficient in terms of attenuating propagating waves and reducing late time reflections. Moreover, the higher-order PML can be placed very close to the wall when analyzing the channel characteristics of time reversal (TR) waves in a multipath indoor environment. Numerical examples of TR wave propagation demonstrate the availability of the proposed method.

The influence of thickness of atomic layer deposited Al2O3 films on nanotextured fluorescent 6H-SiC passivation is investigated. The passivation effect on the light emission has been characterized by photoluminescence and time-resolved photoluminescence at room temperature. The results show that 20nm thickness of Al2O3 layer is favorable to observe a large photoluminescence enhancement (25.9%) and long carrier lifetime (0.86ms). This is a strong indication for an interface hydrogenation that takes place during post-thermal annealing. These result show that an Al2O3 layer could serve as passivation in fluorescent SiC based white LEDs applications.

In this paper, we proposed a 2×2 imaging Multi-Input Multi-Output (MIMO)-Visible Light Communication (VLC) system by employing Space Balanced Coding (SBC) based on two RGB LEDs and integrated PIN array reception. We experimentally demonstrated 1.4-Gbit/s VLC transmission at a distance of 2.5 m. The proposed imaging system not only overcomes the limitation of bandwidth existing in LEDs, but also can reject the second-order nonlinearity distortion. It turned out to be very promising to use integrated antennas in the VLC system in the future.

A series of single-phase Ca9Ln(PO4)7:Eu2+,Mn2+ (Ln = Gd, La, Lu) phosphors with enhanced quantum yields were successfully developed through a topochemical reduction reaction strategy by using elemental aluminum as the reducing agent. Changes were observed both in the spectral shapes and photoluminescence intensities. New broadband emission covering the whole red region and centered at 630 nm from the remote Al reduced Ca9Ln(PO4)7:Eu2+ phosphors was observed, and their PL intensity was found to be greatly enhanced. The remote Al reduced Ca9Gd(PO4)7:Eu2+ reaches 4.3 times higher PL than the phosphors prepared by the traditional reduction method under CO atmosphere with the optimal Eu2+ dopant content. Finally, enhanced white-light emissions were gradually obtained by co-doping Eu2+ and Mn2+ in Ca9Ln(PO4)7, and the PLQY value is raised from extremely low to 61.6%. The mechanism for the changes of luminescence behavior was studied and discussed. This research also provides an enlightening reference for the preparation and development of high efficiency single-phase white light emitting phosphors.

We realize silicon carbide-on-insulator platform based on crystalline 4H SiC and demonstrate high confinement SiC resonators with sub-micron waveguide cross-sectional dimension. The obtained Q (57,000) is the highest Q reported for SiC microring resonators.

We derive full-vectorial nonlinear propagation equations of dual-pumped four-wave mixing in straight waveguides, which are valid in characterizing the one-to-six wavelength multicasting. Special attention is paid to the resulting idler wavelengths and their conversion efficiency, which enables the optimization of the experimental designs, including the incident wavelength and the power of pumps and signal. We validate the model by comparing the numerical simulation to the experimental measurement in a silicon-on-insulator waveguide, for the first time to our best knowledge, and achieve a good agreement. We further derive the general form of the proposed model for the case of using multiple,pumps, which holds a potential to numerically predict the performance of complex wavelength multicasting, and essentially guide the waveguide designs.

In this Letter, we propose a new method for auto-focusing and reconstruction without defocus noise in optical scanning holography. By using a connected domain (CD) to calculate the area of different domains, which are labeled by a connected component, the focus distance can be found via the smallest area of each CD. Meanwhile, the sectional images without defocus noise can also be reconstructed based on the labeled domains. The effectiveness of this method has been verified with a simulation and experiments.

miRNAs are a class of noncoding RNAs important in posttranscriptional repressors and involved in the regulation of almost every biological process by base paring with target genes through sequence in their seed regions. Genetic variations in the seed regions have vital effects on gene expression, phenotypic variation, and disease susceptibility in humans. The distribution pattern of genetic variation in miRNA seed regions might be related to miRNA function and is worth paying more attention to. We here employed computational analyses to explore the clustering pattern and functional effect of SNPs in human miRNA seed regions. A total of 1879 SNPs were mapped to 1226 human miRNA seed regions. We found that miRNAs with SNPs in their seed region are significantly enriched in miRNA clusters. We also found that SNPs in clustered miRNA seed regions have a lower functional effect than have SNPs in nonclustered miRNA seed regions. Additionally, we found that clustered miRNAs with SNPs in seed regions are involved in more pathways. Overall, our results demonstrate that SNPs in clustered miRNA seed regions can take part in more intricate and complex gene-regulating networks with lower functional cost by functional complementarity. Moreover, our results also broaden current knowledge on the genetic variation in human miRNA seed regions.

This paper presents a method to identify the axial location of targets in an optical scanning holography (OSH) system. By combining time reversal (TR) technique with the multiple signal classification (MUSIC) method in OSH, axial location can be detected with high resolution. Both simulation and experimental work have been carried out to verify the feasibility of the proposed work.

We have investigated the use of nanopillar structures on high indium content InGaN amber multiple quantum well (MQW) samples to enhance the emission efficiency. A significant emission enhancement was observed which can be attributed to the enhancement of internal quantum efficiency and light extraction efficiency. The size-dependent strain relaxation effect was characterized by photoluminescence, Raman spectroscopy and time-resolved photoluminescence measurements. In addition, the light extraction efficiency of different MQW samples was studied by finite-different time-domain simulations. Compared to the as-grown sample, the nanopillar amber MQW sample with a diameter of 300 nm has demonstrated an emission enhancement by a factor of 23.8.

E1/E2 defects are the typical negative-U centers in n-type 6H silicon carbide (SiC). They are the main contributors to non-radiative recombination, which limits the carrier lifetime. In this study, two fluorescent 6H silicon carbide (f-SiC) samples and one bulk substrate were characterized via time-resolved photoluminescence (TRPL) and static photoluminescence (PL) measurements, where all the samples were nitrogen-boron co-doped 6H n-type. The existence of E1/E2 defects, which caused the diminution of the internal quantum efficiency (IQE) and luminescence intensity of each sample, was confirmed by applying a carrier dynamics model based on negative-U centers. The carrier dynamics simulation reveals that the density of the E1/E2 defects in bulk 6H SiC is two orders of magnitude higher than that of the f-SiC sample, causing much lower PL intensity in the bulk substrate compared to the two f-SiC samples. The IQE of the two f-SiC samples was extracted from the corresponding TRPL results, where the contrast between their IQE was further confirmed by the related PL measurement results. The slight difference in IQE between the two f-SiC samples was attributed to slightly different E1/E2 defect concentrations. On the other hand, by implementing a steady-state donor-acceptor-pair (DAP) recombination calculation, it was found that the f-SiC sample with lower IQE had a higher DAP transition probability due to the higher doping level. This prompted further optimizations in the f-SiC crystal growth conditions in order to decrease the E1/E2 defects while maintaining the correct doping parameters.

A localized surface plasma coupled LED with modulation bandwidth of 152MHz which was enhanced by 1.65 times relative to grid LED was fabricated for high-speed VLC system, while the light power increased by 1.67 times.

To achieve photon-pair generation scaling, we optimize the quality factor of microring resonators for efficient continuous-wave-pumped spontaneous four-wave mixing. Numerical studies indicate that a high intrinsic quality factor makes high pair rate and pair brightness possible, in which the maximums take place under overcoupling and critical-coupling conditions, respectively. We fabricate six all-pass-type microring resonator samples on a silicon-on-insulator chip involving gap width as the only degree of freedom. The signal count rate, pair brightness, and coincidence rate of all the samples are characterized, which are then compared with the modified simulations by taking the detector saturation and nonlinear loss into account. Being experimentally validated for the first time to the best of our knowledge, this work explicitly demonstrates that reducing the round-trip loss in a ring cavity and designing the corresponding optimized gap width are more effective to generate high-rate or high-brightness photon pairs than the conventional strategy of simply increasing the quality factor. (C) 2018 Chinese Laser Press

This paper presents our laboratory results of growing a new type of compound semiconductor crystal, i.e. fluorescent silicon carbide (f-SiC), by using liquid solution phase epitaxial (LPE) technology. This new type of f-SiC based white LEDs (WLEDs) represents higher luminous efficiency, better light quality and longer lifespan, compared to the current yellow phosphor based white LEDs. Liquid phase epitaxy technology is able to yield a high crystalline quality in terms of structural perfection owing to the fact that it is a near equilibrium process. In addition, the technological equipment required for LPE is relatively inexpensive. The fundamental backgrounds for LPE growth of Al-doped 4H-SiC are first introduced and elaborated by new thermodynamic and crystal growth models. Based on theoretical analyses, the new designed experimental apparatus is then constructed. The experimental results are presented and discussed. Since operational temperature of LPE growth is much lower than that currently used in physical vapour transport (PVT) process, it is expected to save the energy consumption for SiC crystal growth.

Light-emitting silicon carbide is emerging as an environment-friendly wavelength converter in the application of light-emitting diode based white light source for two main reasons. Firstly, SiC has very good thermal conductivity and therefore a good substrate for GaN growth in addition to the small lattice mismatch. Secondly, SiC material is abundant, containing no rear-earth element material as commercial phosphors. In this paper, fabrication of porous SiC is introduced, and their morphology and photoluminescence are characterized. Additionally, the carrier lifetime of the porous SiC is measured by time-resolved photoluminescence. The ultrashort decay time in the order of ∼70 ps indicates porous SiC is very promising for the application in the ultrafast visible light communications.

We derive from Maxwell's equations full-vectorial nonlinear propagation equations of four-wave mixing valid in straight semiconductor-on-insulator waveguides. Special attention is given to the resulting effective mode area, which takes a convenient form known from studies in photonic crystal fibers, but has not been introduced in the context of integrated waveguides. We show that the difference between our full-vectorial effective mode area and the scalar equivalent often referred to in the literature may lead to mistakes when evaluating the nonlinear refractive index and optimizing designs of new waveguides. We verify the results of our derivation by comparing it to experimental measurements in a silicon-on-insulator waveguide, taking tolerances on fabrication parameters into account. (C) 2017 Optical Society of America

We numerically demonstrate dispersion tailoring of a silicon strip waveguide employing Titania-Alumina thin-film coating using a finite-difference mode solver. The proposed structure exhibits spectrally-flattened near-zero anomalous dispersion within the telecom wavelength range. We also numerically predict the wavelength conversion efficiency for degenerate four-wave mixing, and obtain a 3 dB bandwidth of 80 nm.

Genome-wide association studies (GWAS) reveal numerous schizophrenia (SCZ)-associated single-nucleotide polymorphisms (SNPs); however, functional characterizations of the risk variants remain to be established. Using data from 108 SCZ GWAS loci, we performed systematic miRNA binding site screening of 128 SCZ-associated SNPs and found that 2 out of 3 SNPs located in the 3'UTR were predicted to alter 3 miRNAs' binding sites in 2 target genes. Of the identified SNPs, the most genome-wide significant SNP rs4702 (A/G) in the FURIN 3'UTR, previously identified as an SCZ-associated cis-expression quantitative trait loci (downregulated by the risk G allele), is located in the binding site of miR-338-3p in the presence of the risk G allele. Allele-specific downregulation of FURIN by miR-338-3p was validated with a luciferase reporter assay. Furthermore, we demonstrated that miR-338-3p-mediated FURIN inhibition reduced brain-derived neurotrophic factor (BDNF) maturation and secretion in human embryonic kidney 293T cells. Our data reveal that schizophrenia-associated rs4702 G allele-specific downregulation of FURIN by miR-338-3p reduces mature BDNF production. These data help elucidate the mechanism of genetic predisposition toward schizophrenia or other neurodevelopmental diseases.

Two n-type 6H fluorescent SiC (f-SiC) samples have been characterized using thermally stimulated luminescence (TSL) spectroscopy, where the dominant carriers recombination regime has been found via the numerical simulations.

We demonstrate ultrafast nonlinear absorption induced by strong, single-cycle THz fields in bulk, lightly doped 4H silicon carbide. A combination of Zener tunneling and intraband transitions makes the effect as at least as fast as the excitation pulse. The sub-picosecond recovery time makes the observed response the fastest nonlinear modulation scheme for THz signals reported so far.

We have presented the low temperature photoluminescence (PL) measurements of three 6H fluorescent Silicon Carbide (f-SiC) samples. The epilayers of the f-SiC samples were nitrogenboron co-doped and grown by fast sublimation growth process (FSGP) method on the bulk 6H SiC substrates. The doping concentrations of the f-SiC epilayers were determined by secondary ion mass spectroscopy (SIMS) showing strong n-type, strong p-type and slight p-type extrinsic semiconductor doping of each epilayer. The PL intensity of one commercial 6H bulk SiC (TanKeBlue Ltd.) was also measured and applied as the reference. The PL was excited by a diode laser source with wavelength of 405 nm and power of 5 mW. The temperature of the PLmeasurement was ranged from 25K to 300K when the liquid nitrogen cryostat was used, while lower temperature from 5K was achieved when the cryostat with liquid helium was applied. The anomalous temperature dependences of the PL intensity spectrum of f-SiC samples were found. The PL peak energy’s S-shape dependence on the temperature was observed which was caused by nitrogen induced localization effect. For strong p-type f-SiC, one more PL intensity peak at 5 k wasobserved at wavelength of 520 nm, where this extra PL peak was the result of basal plane dislocation and free-to-acceptor recombination.

A nano-patterning approach on silicon dioxide (SiO2) material, which could be used for the selective growth of III-V nanowires in photovoltaic applications, is demonstrated. In this process, a silicon (Si) stamp with nanopillar structures was first fabricated using electron-beam lithography (EBL) followed by a dry etching process. Afterwards, the Si stamp was employed in nanoimprint lithography (NIL) assisted with a dry etching process to produce nanoholes on the SiO2 layer. The demonstrated approach has advantages such as a high resolution in nanoscale by EBL and good reproducibility by NIL. In addition, high time efficiency can be realized by one-spot electron-beam exposure in the EBL process combined with NIL for mass production. Furthermore, the one-spot exposure enables the scalability of the nanostructures for different application requirements by tuning only the exposure dose. The size variation of the nanostructures resulting from exposure parameters in EBL, the pattern transfer during nanoimprint in NIL, and subsequent etching processes of SiO2 were also studied quantitatively. By this method, a hexagonal arranged hole array in SiO2 with a hole diameter ranging from 45 to 75 nm and a pitch of 600 nm was demonstrated on a four-inch wafer.

Transparent conductive aluminum-doped zinc oxide (AZO) layer was deposited on GaN-based near-ultraviolet (NUV) light emitting epitaxial wafers as current spreading layer by a sputtering process. Efforts were made to improve the electrical properties of AZO in order to produce ohmic contact.

Porous silicon carbide (B–N co-doped SiC) produced by anodic oxidation showed strong photoluminescence (PL) at around 520 nm excited by a 375 nm laser. The porous SiC samples were passivated by atomic layer deposited (ALD) aluminum oxide (Al2O3) films, resulting in a significant enhancement of the PL intensity (up to 689%). The effect of thickness, annealing temperature, annealing duration and precursor purge time on the PL intensity of ALD Al2O3 films was investigated. In order to investigate the penetration depth and passivation effect in porous SiC, the samples were characterized by X-ray photoelectron spectroscopy (XPS) and time-resolved PL. The optimized passivation conditions (20 nm Al2O3 deposited at 160 °C with purge time of 20 s, followed by an annealing for 5 min at 350 °C) for porous SiC were achieved and the results indicate that surface passivation by ALD Al2O3 thin films is a very effective method to enhance the luminescence efficiency of porous SiC.

Van der Waals epitaxy (vdWE) has drawn continuous attention, as it is unlimited by lattice-mismatch between epitaxial layers and substrates. Previous reports on the vdWE of III-nitride thin film were mainly based on two-dimensional (2D) materials by plasma pretreatment or pre-doping of other hexagonal materials. However, it is still a huge challenge for single-crystalline thin film on 2D materials without any other extra treatment or interlayer. Here, we grew high-quality single-crystalline AlN thin film on sapphire substrate with an intrinsic WS2 overlayer (WS2/sapphire) by metal-organic chemical vapor deposition, which had surface roughness and defect density similar to that grown on conventional sapphire substrates. Moreover, an AlGaN-based deep ultraviolet light emitting diode structure on WS2/sapphire was demonstrated. The electroluminescence (EL) performance exhibited strong emissions with a single peak at 283 nm. The wavelength of the single peak only showed a faint peak-position shift with increasing current to 80 mA, which further indicated the high quality and low stress of the AlN thin film. This work provides a promising solution for further deep-ultraviolet (DUV) light emitting electrodes (LEDs) development on 2D materials, as well as other unconventional substrates.