Quantitatively Exploring the Effect of a Triangular Electrode on Performance Enhancement in a 4H-SiC Metal-Semiconductor-Metal Ultraviolet Photodetector

A model of novel triangular electrode metal-semiconductor-metal(TEMSM)and conventional electrode metal-semiconductor-metal(CEMSM)detectors is established by utilizing the ISE-TCAD simulator.By comparing the simulated results of TEMSM and CEMSM with experimental data,the model validity is verified and the TEMSM detector shows a superiority of a 113%photocurrent increase of 25.4 nA and similar low dark current of 3.16 pA at 30 V bias over the CEMSM device.Furthermore,the electrode angleα,width W and spacing S are optimized to obtain the enhanced device features including high UV−to-visible rejection ratio and large responsivity,etc.Under 30 V bias,the maximum UV-to-visible rejection ratio,comparable responsivity and external quantum efficiency at 310 nm are 13049,0.1712 A/W and 68.48%for a TEMSM detector with device parameters ofα=60°,W=3μm and S=4μm,respectively.

聚多巴胺磁分子印迹材料制备及其在食用油中黄曲霉毒素B富集中的应用

目的建立了基于聚多巴胺磁性分子印迹聚合物吸附富集食用油中黄曲霉毒素B的方法。方法以多巴胺为功能单体和交联剂,5,7-二甲氧基香豆素为模拟模板分子,一步法在Fe_(3)O_(4) NPs表面制备磁分子印迹聚合物。采用透射电子显微镜和红外光谱仪对该分子印迹材料形态和结构进行表征,研究了其对两种黄曲霉毒素B吸附性能。最终以该印迹材料作为分散固相萃取剂,对影响黄曲霉毒素B吸附的条件进行了优化。结果该分子印迹材料对两种黄曲霉毒素B的吸附模式符合Langmuir理论,对黄曲霉毒素B_(1)和黄曲霉毒素B_(2)最大吸附容量分别为0.460和0.047 mg/g。在最佳萃取条件[材料用量(10 mg)、溶液pH(7)、超声时间(5 min)和1 mL(解吸2次,每次0.5 mL)3%乙酸/乙腈作为解析液]下,结合配有大体积流通池的超高效液相色谱-荧光检测法定量检测,黄曲霉毒素B_(1)和黄曲霉毒素B_(2)浓度分别在0.005~0.500 ng/mL(r=0.9989)和0.001~0.100 ng/mL(r=0.9992)范围内与对应的峰面积呈现良好的线性相关性,检出限分别为0.0024和0.00038 ng/mL,食用油样品加标回收率为93.2%~104.0%,相对标准偏差5.8%~7.7%,且可重复使用至少7次。结论该吸附富集方法具有快速、低廉、选择性高、稳定性好等特点,适用于食用油中黄曲霉毒素B的前处理。

Effects of gate-buffer combined with a p-type spacer structure on silicon carbide metal semiconductor field-effect transistors

An improved structure of silicon carbide metal-semiconductor field-effect transistors （MESFET） is proposed for high power microwave applications. Numerical models for the physical and electrical mechanisms of the device are presented, and the static and dynamic electrical performances are analysed. By comparison with the conventional structure, the proposed structure exhibits a superior frequency response while possessing better DC characteristics. A p-type spacer layer, inserted between the oxide and the channel, is shown to suppress the surface trap effect and improve the distribution of the electric field at the gate edge. Meanwhile, a lightly doped n-type buffer layer under the gate reduces depletion in the channel, resulting in an increase in the output current and a reduction in the gate-capacitance. The structural parameter dependences of the device performance are discussed, and an optimized design is obtained. The results show that the maximum saturation current density of 325 mA/mm is yielded, compared with 182 mA/mm for conventional MESFETs under the condition that the breakdown voltage of the proposed MESFET is larger than that of the conventional MESFET, leading to an increase of 79% in the output power density. In addition, improvements of 27% cut-off frequency and 28% maximum oscillation frequency are achieved compared with a conventional MESFET, respectively.

An Analytical Model of SiGe Heterojunction Bipolar Transistors on SOI Substrate for Large Current Situations

The large current effect of silicon germanium heterojunction bipolar transistors fabricated on thin silicon-on-insulator is included in the model.As the current is two-dimensional,the injection for large current is vertical plus horizontal and is quite different from that of the bulk device.Critical parameters modeling the large current,such as the collector injection width,the hole density and the corresponding potential in the injection region,are discussed,and the influence to the transit time is also analyzed.

The Theoretical Investigation and Analysis of High-Performance ZnO Double-Gate Double-Layer Insulator Thin-Film Transistors

A novel structure of a ZnO thin-film transistor with a double-gate and double-layer insulator is proposed to improve device performance.Compared with the conventional ZnO thin-film transistor structure,the novel thinfilm transistor has a higher on-state current,steeper sub-threshold characteristics and a lower threshold voltage,owing to the double-gate and high-k dielectric.Based on two-dimensional simulation,the potential channel distribution and the reasons for the improvement in performance are investigated.

A new type of Wilkinson dual-frequency power divider with symmetrical transmission line stubs

To realize equal power splitting at two arbitrary gigahertz-frequencies, this paper presents a new type of Wilkinson dual frequency power divider, consisting of three-section transmission lines and a series RLC(resistor, inductor and capacitor)circuit. By equating the [ABCD] matrix of the proposed circuit to that of the quarter-wave impedance transformer, coupled with even/odd mode analyses, the design equations of the proposed network are derived. For verification, two dual-frequency power dividers with dual-band operating frequencies at 0.6 GHz and 3.0 GHz, and 3.8 GHz and 10 GHz respectively are designed and simulated. Simulation results show that the dual-band ratio of the proposed power divider can be as large as 5. Comparisons of the simulation results at X-band and S-band with different power dividers indicate that the proposed dual-band power divider performs better under the scenario of the upper operating frequency extending to X-band.

New 4H silicon carbide metal semiconductor field-effect transistor with a buffer layer between the gate and the channel layer

A new 4H silicon carbide metal semiconductor field-effect transistor （4H-SiC MESFET） structure with a buffer layer between the gate and the channel layer is proposed in this paper for high power microwave applications. The physics-based analytical models for calculating the performance of the proposed device are obtained by solving one- and two-dimensional Poisson＇s equations. In the models, we take into account not only two regions under the gate but also a third high field region between the gate and the drain which is usually omitted. The direct-current and the alternating- current performances for the proposed 4H-SiC MESFET with a buffer layer of 0.2 ~tm are calculated. The calculated results are in good agreement with the experimental data. The current is larger than that of the conventional structure. The cutoff frequency （fT） and the maximum oscillation frequency （fmax） are 20.4 GHz and 101.6 GHz, respectively, which are higher than 7.8 GHz and 45.3 GHz of the conventional structure. Therefore, the proposed 4H-SiC MESFET structure has better power and microwave performances than the conventional structure.