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

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

多层InAs量子点的光致发光研究

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23．6meV，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