Breakdown voltage analysis of Al0.25Ga0.75N/GaN high electron mobility transistors with partial silicon doping in the AlGaN layer

In this paper,two-dimensional electron gas（2DEG） regions in AlGaN/GaN high electron mobility transistors（HEMTs） are realized by doping partial silicon into the AlGaN layer for the first time.A new electric field peak is introduced along the interface between the AlGaN and GaN buffer by the electric field modulation effect due to partial silicon positive charge.The high electric field near the gate for the complete silicon doping structure is effectively decreased,which makes the surface electric field uniform.The high electric field peak near the drain results from the potential difference between the surface and the depletion regions.Simulated breakdown curves that are the same as the test results are obtained for the first time by introducing an acceptor-like trap into the N-type GaN buffer.The proposed structure with partial silicon doping is better than the structure with complete silicon doping and conventional structures with the electric field plate near the drain.The breakdown voltage is improved from 296 V for the conventional structure to 400 V for the proposed one resulting from the uniform surface electric field.     

A novel Si-based photodetector with flat-top and steep-edge spectral response

To meet the requirement of the dense wavelength-division-multiplexed (DWDM) system and optoelectronic integrated circuit, we design a Si-Based InGaAs photodetector, which is fabricated by bonding InGaAs/InP photodetector on a Si-Based dielectric film Fabry–Perot filter. The photodetector can exhibit an extremely good flat-top and steep-edge spectral response through designing the structure of Si-Based dielectric film Fabry–Perot filter. The simulation result of phtodetector demonstrates that the spectral response linewidth, ?at-top and steep-edge characteristics of these photodetectors are suitable to be used in 50 GHz, 100 GHz, 200 GHz DWDM system.     

Growth,characterization and upconversion properties of erbium-doped potassium lithium tantalate niobate single crystals under 975 nm laser excitation

Potassium lithium tantalate niobate single crystals doped with erbium ions are grown by top-seeded solution growth method. The crystals are characterized by X-ray diffraction and differential thermal analysis. The refractive indices of the crystal are measured using ellipsometry method and fitted by Sellmeier equation. The as-grown crystals are tetragonal phase tungsten bronze-type structure with Curie temperature of 271.3 °C. Characteristic Er^3 + absorption bands are observed from 350 to 1100 nm in ultraviolet–visible-near infrared absorption spectra. These crystals emit brightly green and red upconversion fluorescence under 975 nm LD laser excitation, and the steady state upconversion spectra are obtained at room temperature. The red emission intensity increases as the erbium ions concentration increases in crystals. Processes of excited state absorption and energy transfer are responsible for upconversion luminescence. The emission intensities are quadratic dependences on pump power from pump power dependence analyses and deduction of transition rate equation model.     

Fabrication and luminescence behavior of phosphate glass ceramics co-doped with Er3+ and Yb3+

Transparent phosphate glass ceramics co-doped with Er³⁺ and Yb³⁺ in the system P₂O₅Li₂OCaF₂TiO₂ were successfully synthesized by melt-quenching and subsequent heating. Formation of the nanocrystals was confirmed by X-ray powder diffraction. Judd–Ofelt analyses of Er³⁺ ions in the precursor glasses and glass ceramics were performed to evaluate the intensity parameters Ω_2,4,6. Under 975 nm excitation, intense upconversion (UC) and infrared emission (1545 nm) were observed in the glass ceramics by efficient energy transfer from Yb³⁺ to Er³⁺. The luminescence processes were explained and the emission cross section was calculated by Fuchtbauer–Ladenburg (F–L) formula. The results confirm the potential applications of Er³⁺/Yb³⁺ co-doped glass ceramics as laser and fiber amplifier media.     

Stability in a general coupled laser array

For the first time we have presented a method to investigate the stability of quiescent state in a coupled laser array. By introducing tiny perturbation, stability of quiescent state can be known by investigating eigenvalues of coefficient matrix of the corresponding linear differential equations. Only when real parts of the eigenvalues were all negative or zero, the corresponding quiescent state is stable. Two tapes of coupled laser array with loop and linear topological structure were studied respectively. It was found that there were innumerable quiescent states and they could be divided into several types based on phase relation. Some types were stable and others were unstable. Topological structure affects the stability of quiescent state in a coupled laser array.     

103 W in-band dual-end-pumped Ho:YAG laser

An efficient 2?μm in-band pumped Ho:YAG laser was demonstrated. The resonator involves two Ho:YAG crystals, each of which was dual-end-pumped by two orthogonally polarized diode-pumped Tm:YLF lasers. The maximum continuous wave output power of 103?W was achieved, corresponding to a slope efficiency of 67.8% with respect to the incident pump power and an optical-to-optical conversion efficiency of 63.5%. Under Q-switched mode, we obtained 101?W laser output at 30?kHz, corresponding to a slope efficiency of 66.2%. The beam quality or M² factor was found to be less than 2.     

用时间分辨光谱研究红细胞悬液的荧光发射

实验获得了激光照射红细胞悬液的荧光光谱,并分别监测不同荧光峰值波长处强度随时间的衰变过程,测试了其相应的荧光寿命。结果表明,在波长为407nm的激光照射下,红细胞悬液向外发射中心波长分别位于596,628,692nm的荧光光谱,各荧光峰对应衰变过程的平均荧光寿命分别为1.97,13.31,14.58ns。利用荧光强度和吸收率的加和性表示了混合物的总吸收率和总荧光发射强度,通过理论计算获得了红细胞悬液中锌卟啉、原卟啉和其他游离物参与荧光发射的相对含量和相对强度在不同荧光峰位的变化关系,进一步解释了不同峰位处荧光发射强度和平均荧光寿命的变化原因。     

A 3-D numerical heat transfer model for silica aerogels based on the porous secondary nanoparticle aggregate structure

A 3-D finite volume numerical model based on the porous secondary nanoparticle random aggregate structure was developed to predict the total thermal conductivity of silica aerogels. An improved 3-D diffusion-limited cluster–cluster aggregation (DLCA) method was used to generate an approximately real silica aerogel structure. The model includes the effects of the random and irregular nanoparticle aggregate structure for silica aerogels, solid–gas coupling, combined conduction and radiation, nanoparticle and pore sizes, secondary nanoparticle porosity and contact length between adjacent nanoparticles. The results show that the contact length and porosity of the secondary aerogel nanoparticle significantly affect the aerogel microstructure for a give density and, thus, greatly affect the total thermal conductivity of silica aerogels. The present model is fully validated by experimental results and is much better than the model based on a periodic cubic array of full density primary nanoparticles, especially for higher densities. The minimum total thermal conductivity for various silica aerogel microstructures can be well predicted by the present model for various temperatures, pressures and densities.     

An organocatalytic Michael-aldol cascade: formal [3+2] annulation to construct enantioenriched spirocyclic oxindole derivatives

An efficient organocatalytic Michael-aldol cascade reaction for the asymmetric synthesis of spirocyclic oxindole derivatives fused with tetrahydrothiophenes has been developed through a formal [3+2] annulation strategy.     

Advances in the chemical analysis and biological activities of chuanxiong

Chuanxiong Rhizoma (Chuan-Xiong, CX), the dried rhizome of Ligusticum chuanxiong Hort. (Umbelliferae), is one of the most popular plant medicines in the World. Modern research indicates that organic acids, phthalides, alkaloids, polysaccharides, ceramides and cerebrosides are main components responsible for the bioactivities and properties of CX. Because of its complex constituents, multidisciplinary techniques are needed to validate the analytical methods that support CX's use worldwide. In the past two decades, rapid development of technology has advanced many aspects of CX research. The aim of this review is to illustrate the recent advances in the chemical analysis and biological activities of CX, and to highlight new applications and challenges. Emphasis is placed on recent trends and emerging techniques.