Research and Fabrication of UV SAM 4H-SiC APDs with Low Breakdown Voltage and Its p-type Ohmic Contacts

紫外微弱光信号和单光子信号的探测主要应用于激光诱导荧光性生物报警系统、非线性光线隐蔽通讯、非破坏性物质分析、高能物理、光时域反射和空气污染超高灵敏度探测等领域，它要求探测器具有高量子效率、低暗电流、低的过剩噪声和可见盲等特性，4H-SiC雪崩光电探测器（APD）是惟一能够满足这些要求的器件。 近年来，国际上已有研究小组对4H-SiCAPDs进行制备和研究，但所设计的APD结构较为简单，一般由PN结或者PIN结构成，不能有效地解决吸收层厚度对高量子效率、快响应速率和低击穿电压之间相互限制的矛盾；而已报道的分离吸收层与倍增层（SAM）结构4H-SiCAPDs的击穿电压过大；另外，对于金属与p型4...Low-level and single photon ultraviolet (UV) signal detections are mainly used in laser-induced fluorescence biological-agent detection, non-line-of-sight covert communica- tions, non-destructive material analysis, high energy physics, optical time domain reflectometer, ultra-high sensitivity for air contamination detection, and so on. 4H-SiC APD is the only promising UV detector that satisfies lo...学位：理学博士院系专业：物理与机电工程学院物理学系_凝聚态物理学号：B20042401

Photoluminescence of Multilayer InAs Quantum Dots

采用MBE设备生长了多层InAs/GaAs量子点结构,测量了其变温光致发光谱和时间分辨光致发光谱。结果表明多层量子点结构有利于减小发光峰的半高宽,并且可以提高发光峰半高宽和发光寿命的温度稳定性。实验发现,加InGaAs盖层后,量子点发光峰的半高宽进一步减小,最小达到23.6 meV,并且发光峰出现红移。原因可能在于InGaAs盖层减小了InAs岛所受的应力,阻止了In组分的偏析,提高了InAs量子点尺寸分布的均匀性和质量,导致载流子在不同量子点中的迁移效应减弱。Multilayer InAs/GaAs quantum dots structures were grown by molecular-beam epitaxy(MBE).The steady-state and time-resolved photoluminescence of the samples were measured at various temperatures.Results showed that multilayer structures could not only narrow the photoluminescence FWHM(full width at the half maximum) but enhance the stability of the photoluminescence lifetime and FWHM.As for the quantum dots with InGaAs cap layer,the photoluminescent spectra became narrower(the narrowest FWHM was only 23.6meV) and the photoluminescent wavelength became longer.The possible reason for the above phenomena was that the InGaAs cap layer could both release the strains in InAs islands and inhibit segregation of In components,resulting in the weaker migration among different quantum dots

Research and Analysis on Absorption Coefficient of 4H-SiC at Ultraviolet Wavelength

基于已报道的4H-SIC材料在紫外波段(325—390nM)吸收系数的测定,结合经验公式,采用外推和多项式拟合方法分析4H-SIC材料在200—400nM紫外波段的吸收系数,并得到4H-SIC材料的吸收系数与波长的关系式。对4H-SIC吸收系数的分析研究将作为4H-SIC光电探测器结构设计的一个重要依据。Based on the previous reports on the absorption coefficients of 4H-SiC at 325—390nm,the extrapolation and polynomial fitting methods for analysis of the absorption coefficients of 4H-SiC at 200—400nm was established.And the relationship between the absorption coefficient and the wavelength was obtained.福建省自然科学基金项目资助(No.2009J05151);厦门市科技计划项目(No.350z20031076)资

A study of p-type Ohmic contact for 4H-SiC avalanche photodetector

对4H-SiC雪崩光电探测器的Ti/Al/Au p型欧姆接触进行了详细的研究。通过线性传输线模型(LTLM)测得经930℃退火后欧姆接触的最小比接触电阻为5.4×10~(-4)Ωcm~2。分别用扫描电子显微镜(SEM)、俄歇电子能谱(AES)、X射线光电子能谱(XPS)和X射线衍射谱(XRD)对退火前后的表面形貌、金属之间以及金-半接触界面之间相互反应及扩散情况进行测试与分析,发现了影响欧姆接触性能的主要原冈。对采用此欧姆接触制备的4H-SiC雪崩光电探测器进行测试,发现器件的击穿电压约为-55 V,此时其p型电极处的电压降仅为0.82 mV,可以满足4H-SiC雪崩光电探测器在高压下工作的需要。The p-type Ohmic contact of Ti/Al/Au multiple metal alloy for 4H-SiC avalanche photodetector(APD)was investigated and the lowest specific contact resistance of 5.4×10~(-4)Ωcm~2 was achieved by the linear transmission line method(LTLM).The scanning elec- tron microscope(SEM),Auger electron spectroscopy(AES),X-ray photoelectron spectroscopy (XPS)and Panalytical X'pert PRO X-ray diffraction(XRD)were measured to analyze the contact morphology,chemical composition and the phase formation of the samples before and after annealing.In addition,the electrical properties of 4H-SiC APDs with the same p-type Ohmic contact were also measured.Near the breakdown voltage of about-55 V,the voltage descent at p electrode was as low as 0.82 mV,which showed that the Ohmic contact can satisfy the requirement of 4H-SiC APD

Separate Absorption and Multiplication 4H-SiC Ultraviolet Avalanche Photodetector

设计和制备了吸收层和倍增层分开的4H-SiC穿通型雪崩紫外光电探测器.设计器件的倍增层和吸收层厚度分别为0.25和1μm.采用multiplejunctionter mination extension(MJTE)方法减少器件的电流集边效应和器件表面电场.对器件的暗电流、光电流和光谱响应进行了测量.器件在55V的低击穿电压下获得了一个高的增益(>104);穿通前器件暗电流约为10pA数量级;0V偏压下器件光谱响应的紫外可见比大于103.光谱响应的峰值波长随反向偏压的增大而向短波方向移动,在击穿电压附近光谱响应的峰值波长移到210nm,此波长远远小于在0V时的响应峰值.结果显示器件在紫外光探测中具有优良的性能.A 4H-SiC avalanche photodetector(APD)with separate absorption and multiplication layers was designed and fabricated.The thicknesses of the absorption and multiplication epilayers were designed as 0.25 and 1μm,respectively.A multiple junction termination extension(MJTE)was used to eliminate the electric field crowding effect at the edge and to reduce the surface electric field.Dark current,photocurrent,and spectral responsivity were measured.High gain(>104)was achieved at a low breakdown voltage,and the dark current was on the order of about 10pA before device was punched through.The ratio of responsivity at 260nm to that at 380nm was higher than 103.A new phenomenon was observed in its spectral responsivity.The response wavelength peak shifted to shorter wavelength as the reverse bias was increased.Near breakdown voltage the peak of the response wavelength was located at 210nm,which was shorter than that at 0V.These results show that the samples have good performance for ultraviolet detection

内外激励作用下的复合行星轮系均载特性分析

当前针对周转轮系均载问题的研究，侧重分析单个激励变化下的均载行为，缺乏调查内外激励共同变化时的均载机理，以致在众多影响轮系均载的激励因素中，难以找出决定均载行为的关键激励，从而高效提升轮系均载性能。为研究这一问题，提出并建立了均载性能的多因素分析模型，将复合行星轮系“平移-扭转”动力学模型与正交试验法相结合，计算不同激励配置下的动态均载系数；采用信噪比和方差分析法，量化和比较各激励对均载系数的影响权值，找出并优化决定均载的关键激励。计算结果表明，内部激励对均载性能的影响远大于外部激励，适当增加轴承间隙可以提升均载性能，减小中心构件的传递误差能最为高效地提升均载性能

Third-order nonlinear optical response of silicon nanostructures dispersed in organic solvent under 1064 nm and 532 nm laser excitations

Silicon nanostructures are dispersed into an organic solvent and the third order optical properties of the system are studied by z-scan technique under 1064 nm and 532 nm excitations. The experiment results show that the silicon nanostructures exhibit self-focus and saturable absorption with both excitation wavelengths. Nonlinear absorption results suggest that a new optical bleaching band exists under 532 nm excitation, and a two-step mechanism is tentatively put forward to explain the saturable absorption under 1064 nm excitation. (c) 2006 Elsevier B.V. All rights reserved

Surface damage of inductively coupled plasma etched SiC on different work pressure

采用CF4/O2作为刻蚀气体,对不同工作压强下ICP刻蚀SiC材料的刻蚀速率以及随之引入的刻蚀损伤进行了研究.结果表明,随着工作压强的增加,ICP刻蚀S iC材料的速率先缓慢增加,然后急剧降低.通过XPS光电子能谱分析发现刻蚀后样品表面的F、O含量均有所增加,表面污染加剧,刻蚀引入的损伤随着工作压强的增加而增加.4H silicon carbide(SiC) was dry etched in an inductively coupled plasma(ICP) system,using CF4/O2 gas mixtures.Etch rate and surface damage induced by ICP etching have been investigated as a function of the work pressure.We found that the etch rate of SiC initially increased slightly and then decreased rapidly with the increase of work pressure.It was also observed that the F and O radical concentration on the etched surface,which was obtained by X-ray photoelectron spectroscopy measurements,increased.The surface damage induced by ICP etching increased with the work pressure