InGaN/GaN多量子阱热退火的拉曼光谱和荧光光谱

通过拉曼光谱及荧光光谱测量研究了采用低压金属有机化学沉积(MOCVD)方法生长的InGaN／GaN多量子阱高温快速热退火处理对量子阱光学性质的影响。观测到退火后InGaN／GaN量子阱的拉曼光谱E2,A1(LO)模式的峰位置出现了红移,而且该振动峰的半高宽也有微小变化。温度升高退火效果更明显。退火使量子阱内应力部分消除,同时In,Ga原子扩散出现相分离使拉曼谱表现出变化。在常温和低温下的光荧光谱表明,退火处理的量子阱发光主峰都出现了红移;而且低温退火出现红移,退火温度升高相对低温退火出现蓝移;同时在低温荧光光谱里看到经过退火处理后原发光峰中主峰旁边弱的峰消失了。讨论了退火对多量子阱光学性质的影响。     

InGaN/GaN多量子阱蓝色发光二极管的实验与模拟分析

分别采用量子阱模型和量子点模型对蓝色InGaN/GaN多量子阱发光二极管电学和光学特性进行模拟,并和实验测量结果进行了比对,结果发现,量子点模型的引入,很好地解决了I-V和电致发光二方面的实验与理论模型间符合程度不好的问题.同时,在I-V曲线特性模拟中发现,在量子点理论模型的基础上,只有考虑到载流子的非平衡量子传输效应,才能得到和实验相接近的I-V曲线,揭示着在InGaN/GaN 多量子阱发光二极管电输运特性中,载流子的非 关键词： InGaN/GaN 发光二极管 数值模拟 量子点模型     

利用C-V法研究GaN基蓝光LED的多量子阱结构

利用C-V测量法研究了GaN基高亮度蓝光发光二极管的InGaN/GaN多量子阱结构(MQWs),通过样品的C-V曲线及对应的杂质浓度分布曲线得出MQWs的结构特性.实验结果表明:MQWs为5个周期的InGaN/GaN多量子阱.室温下InGaN阱层的平均阱宽为2.00nm,阱层的平均杂质浓度为7.12×1018 cm-3,GaN垒层的平均垒宽为12.32nm,垒层的平均杂质浓度为0.82×1018 cm-3.温度降低,InGaN阱宽变窄,杂质浓度增大,而GaN垒宽变宽,杂质浓度降低.     

金属有机化学气相沉积外延技术生长GaN基半导体发光二极管和激光二极管(Ⅱ)

如今，InGaN／GaN基量子阱发光二极管已经商业化，而且InGaN／GaN基量子阱激光二极管已实现连续波室温运转，使用寿命超过10000小时，虽然如此，但还没有完全搞清楚这些器件的发光机理．试验中通常使用连续输出He-Cd激光器（325nm）作光源，或者使用20—50mA注入电流来研究In—GaN量子阱样品或发光二极管光学性质，本文上篇研究了量子阱厚度与发光二极管发光功率的关系，lnGaN和GaN之间的晶格失配产生压电场，从而导致量子束缚斯塔克效应，而量子束缚斯塔克效应强     

影响GaN基蓝光LED能带结构与光谱特性关系的仿真研究

本文采用Silvaco TCAD软件对GaN基InGaN/GaN量子阱蓝光发光二极管(LED)的光谱特性进行了仿真研究。研究结果表明:光谱会随着注入电压的增加而产生蓝移现象,并出现0.365μm处的紫外光发光峰;发光效率在正向电流较小时增长很快,随着正向电流进一步增加而逐渐趋于饱和;随着量子阱中In组分和量子阱阱层厚度的增加,发光光谱出现红移现象,并且发光效率下降。仿真结果对GaN基InGaN/GaN量子阱结构蓝光LED的设计和优化提供一定的依据。     

荧光法测定半导体禁带宽度

光学带隙或禁带宽度是半导体材料的一个重要特征参数.本文以3个具有代表性的InGaN/GaN多量子阱结构作为研究对象,深入探讨了荧光法测定某个目标温度下InGaN阱层的光学带隙所需要满足的测试条件.由于InGaN阱层是一种多元合金且受到来自GaN垒层的应力作用,所以该阱层中不仅存在着杂质/缺陷相关的非辐射中心,也存在着组分起伏诱发的局域势起伏以及极化场诱发的量子限制斯塔克效应.因此,为了获得目标温度下InGaN阱层的较为精确的光学带隙,提出了荧光测量至少应满足的测试条件,即必须消除该目标温度下非辐射中心、局域中心以及量子限制斯塔克效应对辐射过程的影响.     

三元系和四元系GaN基量子阱结构的显微结构

GaN基量子阱是光电子器件如发光二极管、激光二极管的核心结构。实验表明,采用InGaN/GaN三元和AlInGaN/GaN四元两种不同量子阱结构的激光二极管的发光性质和发光效率有明显差别,研究了这两种不同量子阱结构的显微特征。利用原子力显微镜表征了样品的(001)面;通过高分辨X射线衍射对两种量子阱结构的(002)面作ω/2θ扫描测得其卫星峰并分析了两种不同量子阱结构的界面质量;利用X射线衍射对InGaN/GaN和AlInGaN/GaN这两种量子阱的(002)、(101)、(102)、(103)、(104)、(105)和(201)面做ω扫描,进而得到其摇摆曲线。最后利用PL谱研究了它们的光学性能。通过这些显微结构的分析和研究,揭示了InGaN/GaN三元和AlInGaN/GaN四元两种不同量子阱结构宏观性质不同的结构因素。     

InGaN/GaN多量子阱结构发光二极管发光机理转变的低频电流噪声表征

本文对InGaN/GaN多量子阱结构发光二极管开启后的电流噪声进行了测试, 结合低频电流噪声的特点和载流子之间的复合机理, 研究了低频电流噪声功率谱密度与发光二极管发光转变机理之间的关系. 结论表明, 当电流从0.1 mA到10 mA逐渐增大的过程中, InGaN/GaN发光二极管的电流噪声行为从产生-复合噪声逐渐接近于低频1/f噪声, 载流子的复合机理从非辐射复合过渡为电子与空穴之间载流子数的辐射复合, 并具有标准1/f噪声的趋势, 此时多量子阱中的电子和空穴之间的复合趋向于稳定. 本文的结论提供了一种表征InGaN/GaN多量子阱发光二极管发光机理转变的有效方法, 为进一步研究发光二极管中载流子的复合机理、优化和设计发光二极管、提高其发光量子效率提供理论依据.     

引入n型InGaN/GaN超晶格层提高量子阱特性研究

利用金属有机物化学气相淀积技术在蓝宝石衬底上生长了InGaN/GaN量子阱结构. 研究了引入n型InGaN薄层或InGaN/GaN超晶格层的量子阱特性,结果表明通过引入n型InGaN薄层或InGaN/GaN超晶格层缓解了量子阱有源区中的应力,改善了多量子阱表面形貌,减少了V型缺陷密度,而且提高了多量子阱的光致发光强度,从而也改进了LED的发光效率. 关键词： InGaN/GaN多量子阱 原子力显微镜 X射线双晶衍射 光致发光     

In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱性质的影响

利用x射线三轴晶衍射和光致发光谱研究了生长参数In源流量与Ⅲ族流量之比对InGaN/GaN多量子阱结构缺陷(如位错密度和界面粗糙度)和光致发光的影响.通过对（0002）对称和（1012）非对称联动扫描的每一个卫星峰的ω扫描，分别测量出了多量子阱的螺位错和刃位错平均密度，而界面粗糙度则由（0002）对称衍射的卫星峰半高全宽随级数的变化得出.试验发现多量子阱中的位错密度特别是刃位错密度和界面粗糙度随In源流量与Ⅲ族源流量比值的增加而增加，导致室温下光致发光性质的降低，从而也证明了刃位错在InGaN/GaN 关键词： x射线三轴晶衍射 界面粗糙度 位错 InGaN/GaN多量子阱     

SETUP AND APPLICATION OF SCANNING NEAR-FIELD OPTICAL MICROSCOPY

The research on the setup and application of scanning near-field optical microscopy (SNOM) performed in our laboratory is reviewed in this report. We have constructed a versatile low temperature scanning near-field optical microscope with the capability of near-field imaging and spectroscopy, operating at liquid nitrogen temperature. A special designed coaxial double lens was used to introduce the illumination beam through a 200μm fiber; the detected optical signal was transmitted via a fiber tip to an avalanche photon detector. The performance test shows the stability of the new design. The shear force image and optical image of a standard sample are shown. A system of SNOM working at room temperature and atmosphere was used to characterize semiconductors and bio-molecular samples. It revealed the unique features of semiconductor microdisks in the near-field that is significantly different from that of far-field. The effects of different geographic microstructures on the near-field light distribution of InGaP, GaN, and InGaN multi-quantum-well microdisk were observed.     

Theoretical near-field optical properties of branched plasmonic nanoparticle networks

Extended branched networks of single-nanoparticle chains have recently been self-assembled from colloidal suspensions. In particular, gold nanoparticle linear chains and complex chain networks have revealed unique signatures of plasmon modes in their extinction spectra. In this Letter, we investigate theoretically their near-field optical properties and show that a real space mapping of these modes can be achieved with a photon scanning tunneling microscope setup. A distinct subwavelength patterning of the optical near-field gives rise to well-resolved photon scanning tunneling microscope images that can be used to identify the network segments able to efficiently carry optical energy.     

Neutron,photon and proton energy spectra at high altitude measured using a phoswich-type neutron detector

Neutron energy spectrum from 7 to 180 MeV, photon energy spectrum from 4 to 50 MeV and proton energy spectrum from 94 to 145 MeV were measured simultaneously using a phoswich-type neutron detector with particle discrimination methods at atmospheric depth of 249 g/cm², a vertical cut-off rigidity of 10.2 GV and at a heliocentric potential of 312 MV. We compared our results with other measured and calculated particle energy spectra. Our measured results give a large, sharp neutron peak around 70 MeV, although Bonner balls show a broad peak around 100 MeV due to low energy resolution. The measured photon and proton spectra are between the calculated energy spectra. This onboard study provides the first experimental neutron energy spectrum over 10 MeV with a high-energy resolution.     

The shape of the self-activated cathodoluminescence band in ZnS: Cl crystals

The shape of the self-activated (SA) cathodoluminescence (CL) band of ZnS: Cl crystals was measured at temperatures in the range from liquid nitrogen to room temperature. Around the SA CL band maximum the shape is Gaussian. For the low and high energy regions of the band the shape becomes exponential. These results are discussed in terms of the Dow and Redfield [1] internal electric microfield model for exponential edges. The shape parameters for the ZnS self-activated cathodoluminescence band are given in table 1. A spectral correction procedure was employed to obtain the spectra in absolute terms (photons emitted per second in a constant bandwidth resolution interval) from the raw count-rate spectra and the vital importance of this correction is emphasised. When the temperature is decreased, as usually reported, the peak of the uncorrected self-activated band shifts to lower energies. The peak of the corrected band however shifts in the opposite direction, i.e., to higher energies. This corrected change is in agreement with that of the edge emission band, that it is in agreement with the increase in the width of the forbidden energy gap with decreasing temperature in ZnS (table 2). The temperature dependence of the blue-silver (B-Ag_I) and the red-tin (R-Sn) impurity bands in cubic structure ZnS were also investigated. It was found that the uncorrected and corrected B-Ag_I peak energy decreases whilst that of the R-Sn band increases as the temperature is reduced.     

近三相点氮分子固体的低温红外吸收特性研究

利用自主研制的低温液体/固体制备系统制备出了均匀、透光性好的氮分子固体冰层, 测量了其近三相点的红外吸收谱, 在频率2222–2439 cm^-1处观察到了一个宽的吸收带, 且最强峰位位于2288 cm^-1.基于非谐振子模型计算了氮分子的振动频率, 解释了实验中得到的固体中氮分子的红外吸收带主要由氮分子的基频振动及基频振动与转动耦合引起.     

Temperature dependence of aluminum nitride reflectance spectra in vacuum ultraviolet region

Temperature dependence of optical reflectance spectra in vacuum ultraviolet region for aluminum nitride has been measured on high-quality single crystal with synchrotron radiation. The dominant structure due to the interband transition is observed at photon energy around 7.7 eV. With decreasing temperature, the energy position of the dominant structure in the reflectance spectra shifts towards higher energy. The experimental data has been fitted to the Bose-Einstein expression and the obtained parameter related to the strength of the electron-phonon interactions is much smaller than that for the peak at 6.2 eV, suggesting that the higher-lying interband transition energy decreases more slowly with increasing temperature in aluminum nitride (AlN).     

一种聚噻吩(Pt)衍生物在液氮条件下的电致发光性能

成功地试制了用一种聚噻吩（Pt)衍生物作发光活性物质的发光二极管,报导了该元件在液氮（－200℃）中的电致发光特性。     

Free excitons at room temperature in cadmium telluride : A photoelectrochemical evidence

Photoelectrochemical experiments with n-type cadmium telluride electrodes are reported. When the semiconductor samples are sufficiently pure and exhibit a low free carrier concentration, the photocurrent vs. photon energy characteristic, at fixed potential, presents an intense and narrow peak which may be correlated to the excitonic absorption of CdTe. A forbidden gap energy value is deduced E_g = 1.475 eV at room temperature.     

Resonant Raman scattering in germanium

We have studied the spectral dependence of the first order Raman scattering cross section of Ge at room and liquid nitrogen temperatures in the energy region containing the E₁ and E₁ + Δ₁ optical gaps. This region was covered by a fine mesh of points obtained from the discrete lines of three gas lasers and a cw continuously tunable dye laser. Only one resonant peak was observed, as opposed to the two peaks that characterise the absorption and reflection spectra in this region. The shape of this resonance peak can be explained as due to the changes in the electronic polarizability produced by phonon-induced wave function mixing of the spin-orbit split Λ valence band doublet. The observed temperature shift in the resonant energy is much smaller than the one predicted from the known shifts of the optical gaps with temperature. Furthermore the resonant peak at room temperature appears shifted to higher energies when compared with the theoretical peak calculated from the room temperature optical constants. The resonant Raman peak appears to shift with increasing temperature by the full thermal expansion effect plus only a fraction of the electron-phonon interaction shift seen in the optical constants.     

Modifying optical properties of ZnO nanowires via strain-gradient

We conduct systematical cathodolumiuescence study on red-shift of near-band-edge emission energy in elastic bent ZnO nanowires with diameters within the exciton diffusion length （- 200 nm） in liquid nitrogen temperature （81 K）. By charactering the emission spectra of the nanowires with different; local curvatures, we find a linear relationship between strain-gradient and the red-shift of near-band-edge emission photon energy, an elastic strain-gradient effect in semiconductor similar to the famous flexoelectric effect in liquid crystals. Our results provide a new route to understand the inhomogeneous strain effect on the energy bands and optical properties of semiconductors and should be useful for designing advanced nano-optoelectronic devices.