A self-powered sensitive ultraviolet photodetector based on epitaxial graphene on silicon carbide

A self-powered graphene-based photodetector with high performance is particularly useful for device miniaturization and to save energy.Here,we report a graphene/silicon carbide(SiC)-based self-powered ultraviolet photodetector that exhibits a current responsivity of 7.4 m A/W with a response frequency of over a megahertz under 325-nm laser irradiation.The built-in photovoltage of the photodetector is about four orders of magnitude higher than previously reported results for similar devices.These favorable properties are ascribed to the ingenious device design using the combined advantages of graphene and SiC,two terminal electrodes,and asymmetric light irradiation on one of the electrodes.Importantly,the photon energy is larger than the band gap of SiC.This self-powered photodetector is compatible with modern semiconductor technology and shows potential for applications in ultraviolet imaging and graphene-based integrated circuits.     

应用方位反向技术提取反射镜零重力面形

为了预估碳化硅反射镜在空间零重力环境下的面形精度,本文开展了在地面环境下利用方位反向技术提取碳化硅反射镜零重力面形的研究。首先,介绍了方位反向技术提取零重力面形的理论依据;其次,利用有限元分析软件,分析了方位反向对反射镜面形的影响;然后,按照试验流程,先后检测了反射镜在0°和180°状态的面形精度,计算两次检测数据的平均值,得到了反射镜零重力面形。结果表明:反射镜地面零重力面形误差RMS值为12.3 nm,能够满足设计指标要求。最后,对数据可信度进行了分析,确认了试验数据真实可信。该结果预示了反射镜在空间零重力环境下的面形精度,对反射镜光学加工与装调有重要的指导意义。     

SiC表面C 1s谱最优拟合参数的研究

提出了一种新的,用未限定拟合峰位置、半高宽和峰面积的X射线光电子谱拟合方法,研究了拟合峰的数目、函数类型及背景对SiC表面C 1s谱拟合结果的影响,并与样品表面宽扫描X射线光电子谱和红外掠反射吸收谱相对照,确定了SiC表面C 1s谱的最优拟合参数,获得了与文献中数值相同的 C 1s束缚能. 为SiC及其他材料表面元素窄扫描X射线光电子谱的拟合和化学态结构的鉴定奠定了基础. 关键词： SiC X射线光电子谱 C 1s谱     

长条型SiC反射镜轻量化及支撑结构的设计

从满足空间光学遥感器反射镜在复杂工况下综合面形误差要求的角度出发,介绍了长条型反射镜柔性支撑结构材料的选择,讨论了反射镜轻量化及柔性支撑结构的设计方法,采用有限元法进行了工程分析及多次迭代优化,设计出了一种在不同重力方向下引入面形误差变化量RMS值小于λ/40(λ=632.8nm)的反射镜柔性支撑结构。检测实验证明,各项指标均满足设计要求。     

Defect reduction in sublimation grown SiC bulk crystals

For several years the major focus of material issues in SiC substrates was laid on the reduction of macroscopic defects like polytype inclusions, low angle grain boundaries and micropipes. Although significant improvements have been achieved, there are still shortcomings in material quality that have to be overcome. Since it is clear that dislocations are the main reason for degradation in power devices the prevailing attention has shifted to that field of material research. The aim of our work was to investigate the mechanisms that affect the generation of macroscopic and microscopic defects during sublimation growth. Intense studies were utilized on dislocation and stacking fault formation. For this reason we systematically varied parameters of the growth process and applied several methods for the characterization to evaluate material properties most precisely, e.g. KOH-defect-etching, X-ray-diffraction, electron microscopy and optical microscopy. The investigations were accompanied by failure analysis of devices of the Schottky type. We found out that for the improvement of substrate quality emphasis has to be laid on the reduction of thermoelastic stress in the growing crystal. From results of numerical calculations we were able to derive moderate growth conditions with reduced temperature gradients prevailing during the growth process. As a consequence we succeeded in decreasing the defect concentration. The best value so far achieved for the sum of both BPD and TED was 7×10³ cm⁻².     

Circular and rectangular via holes formed in SiC via using ArF based UV excimer laser

Circular via holes with diameters of 10, 25, 50 and 70 μm and rectangular via holes with dimensions of 10 μm × 100 μm, 20 μm × 100 μm and 30 μm × 100 μm and drilled depths between 105 and 110 μm were formed in 300 μm thick bulk 4H-SiC substrates by Ar/F₂ based UV laser drilling (λ = 193 nm) with a pulse width of ∼30 ns and a pulse frequency of 100 Hz. The drilling rate was linearly proportional to the fluence of the laser, however, the rate decreased for the larger via holes. The laser drilling produces much higher etch rates (229-870 μm/min) than conventional dry etching (0.2-1.3 μm/min) and the via entry can be tapered to facilitate subsequent metallization.     

Effect of magnetic field on electrocodeposition behavior of Ni–SiC composites

In this paper, an external magnetic field was applied in the electrodeposition of Ni–SiC composites, and its effects on surface morphology, SiC content, and crystal orientation were examined. It was found that the magnetic field modified the surface morphology and the orientation of the composites and significantly increased the SiC content. The phenomenon can be attributed to the change of charge transfer reactions and the mass transport process through the micromagnetohydrodynamic effect.     

耐高温碳化硅纤维的制备与性能

采用聚硅碳硅烷（PSCS）与乙酰丙酮铝反应，合成出聚铝碳硅烷（PACS）陶瓷先驱体聚合物.经熔融纺丝、空气不熔化、烧成与高温烧结等工艺， 制备性能优异的耐高温碳化硅纤维SiC(Al).经29Si MAS NMR、 XRD、 Raman谱、AES与SEM等一系列分析表明，该纤维的化学组成和结构与普通碳化硅纤维显著不同，具有近化学计量比组成，氧、游离碳以及SixCyOz相的含量大大低于普通碳化硅纤维，这是其高温稳定的主要原因.在制备过程中铝作为烧结助剂起到了使纤维致密化与抑制晶粒快速增长的作用.     

沿[1 ■00]方向升华法生长6H-SiC单晶

本文采用升华法沿着垂直于c轴方向的[1 ■00]方向生长6H-SiC单晶。利用光学显微镜对晶体表面及腐蚀后的晶片进行观察,发现沿[1 ■00]方向生长出的单晶与传统方法沿[0001]方向生长单晶有很多的不同之处,多型对于籽晶的继承性非常强,但是在生长过程中多型夹杂不会发生,该方法生长的晶体中没有发现螺位错(微管)缺陷。     

超轻量化SiC反射镜有限元分析及应用

对超轻量化SiC反射镜进行了有限元分析。设计了超轻量化SiC反射镜的镜体结构。采用MSC.Nastran分析软件对其进行了有限元工程分析。分析结果表明,可满足SiC反射镜面形精度的要求和轻量化的要求。介绍了一种SiC反射镜无镜框支撑结构。