Si衬底MOCVD生长GaN/InGaN多量子阱缺陷TEM研究

用透射电子显微镜对Si衬底生长GaN/InGaN多量子阱材料进行横断面测试,在衬底和缓冲层区域进行高分辨电子显微成像(HRTEM)、电子衍射衬度成像、选区电子衍射成像,在量子阱附近区域进行了双束近似电子衍衬像对其位错特性进行研究;用场发射扫描电子显微镜对饱和KoH溶液腐蚀前后材料成像.结果发现,AIN缓冲层具有多孔结构,高温GaN层位错平均密度达108cm-2,同扫描电子显微镜得到的六角腐蚀坑密度一致,量子阱以下发现大量位错发生90°弯曲,而使穿过量子阱位错密度大大降低.在线位错中,以刃位错居多,其次是混合位错,所观察区域几乎未见螺位错.     

Si衬底GaN基多量子阱外延材料的TEM研究

本文采用高分辨透射电子显微技术对在Si衬底生长的GaN基多量子阱外延材料的位错特征、外延层与衬底的晶体取向关系及界面的结晶形态等微观结构进行了分析和研究.结果表明:Si衬底生长的GaN与衬底有一定的取向关系;材料在MQW附近的穿透位错密度达108 cm-2量级,且多数为刃型位错;样品A的多量子阱下方可见平行于界面方向的...     

Si衬底InGaN/GaN多量子阱LED外延材料的微结构

用透射电子显微镜(TEM)和X射线双晶衍射仪(DCXRD)对在Si(111)衬底上生长的InGaN/GaN多量子阱(MQW)LED外延材料的微结构进行了观察和分析.从TEM高分辨像观察到,在Si和AlN界面处未形成SixNy非晶层,在GaN/AlN界面附近的GaN上有堆垛层错存在,多量子阱的阱(InGaN)和垒(GaN)界面明锐、厚度均匀;TEM和DCXRD进一步分析表明MQW附近n型GaN的位错密度为10acm-2量级,其中多数为b=1/3〈112-0〉的刃位错.     

Si衬底InGaN/GaN多量子阱LED外延材料的微结构

用透射电子显微镜(TEM)和X射线双晶衍射仪(DCXRD)对在Si(111)衬底上生长的InGaN/GaN多量子阱(MQW)LED外延材料的微结构进行了观察和分析.从TEM高分辨像观察到,在Si和AlN界面处未形成SixNy非晶层,在GaN/AlN界面附近的GaN上有堆垛层错存在,多量子阱的阱(InGaN)和垒(GaN)界面明锐、厚度均匀;TEM和DCXRD进一步分析表明MQW附近n型GaN的位错密度为10acm-2量级,其中多数为b=1/3〈112-0〉的刃位错.     

InGaN/GaN多量子阱纳米线发光二极管制备及研究

用SiO2纳米图形层作为模板在以蓝宝石为衬底的n-GaN单晶层上制备了InGaN/GaN多量子阱纳米线,并成功实现了其发光二极管器件(LED).场发射扫描电子显微镜(FESEM)的测量结果表明,InGaN/GaN多量子阱纳米线具有光滑的表面形貌和三角形的剖面结构.室温下阴极射线荧光谱(CL)的测试发现了位于461 nm...     

超晶格插入层对Si基上GaN薄膜位错密度的影响

为了降低MOCVD外延生长Si基GaN的缺陷密度,尝试引入超品格插入层.界面突变的超晶格插入层能有效地阻挡由缓冲层延伸出来的位错.即使超晶格本身也产生位错,但位错的产生率比阻挡率低,所以超晶格总体起阻挡作用,可以减少后续生长的 HT-GaN(高温氮化镓)的位错密度.研究了超晶格厚度对 HT-GaN 的位错密度的影响.比较了超晶格厚度不同的3个样品,并采用高分辨双晶X射线衍射(DCXRD)对CaN进行结晶质量的分析,分别用 H3PO4 H2SO4 混合溶液和熔融 KOH 对样品进行腐蚀并用扫描电子显微镜(SEM)对腐蚀的样品进行观察.用 H3PO4 H2SO4 腐蚀过的样品比用KOH 腐蚀过的样品的位错密度大,进一步验证了之前有报道过的 H3PO4 H2SO4 溶液同时腐蚀螺位错和混合位错而 KOH只腐蚀螺位错.分析结果表明.引入适当厚度的超晶格插入层,可以有效地降低后续生长的 GaN 的位错密度.     

6H-SiC衬底上采用不同厚度AlN缓冲层对GaN外延层的影响

采用不同厚度AlN作为缓冲层在6H-SiC衬底上生长了GaN外延层,并利用X射线衍射,拉曼散射和透射电子显微镜等对GaN性质进行了研究。AlN缓冲层的应变状态对GaN的晶体质量和表面形貌有很大影响。较厚的AlN缓冲层会导致GaN表面出现裂纹,而太薄的AlN缓冲层会导致GaN层较高的位错密度,从而恶化器件性能。分析了GaN产生裂纹和高位错密度的机制,并采用较优厚度（100nm）的AlN缓冲层生长出高质量的GaN外延层。     

采用Ga(In,As)P异变缓冲层的GaP/Si衬底上InAs量子阱

本工作在GaP/Si衬底上基于In0.83Al0.17As异变缓冲层实现了InAs/In0.83Al0.17As量子阱的生长.研究了GaxIn1-xP和GaAsyP1-y递变缓冲层对量子阱结构材料性能的影响.采用GaxIn1-xP组分渐变缓冲层的样品X射线衍射倒易空间衍射峰展宽更小,表明样品中的失配位错更少.两个样品均...     

基于图形化蓝宝石衬底的HB-LED研究进展

为了制作高亮度LED,需要在图形化蓝宝石衬底上生长GaN材料。通过光刻在平坦蓝宝石衬底上制作掩膜图形,通过刻蚀将图形转移到蓝宝石衬底,得到图形化蓝宝石衬底。在图形化蓝宝石衬底上进行GaN的侧向外延生长,并做后续处理,就制成了基于图形化蓝宝石衬底的高亮度LED。图形化蓝宝石衬底上GaN的侧向外延生长使得外延材料的位错密度从1010 cm-2降低到107 cm-2,这减少了发生非辐射复合的载流子,多量子阱发射更多的光子,LED的内量子效率提高。此外,图形化蓝宝石衬底能够有效散射从多量子阱射出的光线,使得出射光射到逃离区的几率更大,从而提高光萃取率。内量子效率和光萃取率的提高大大改善了LED的光电特性。     

分子束外延HgCdTe薄膜位错密度的研究

本文报道在晶格失配ＧａＡｓ衬底上分子束外延ＨｇＣｄＴｅ薄膜的位错密度研究结果．用位错腐蚀坑密度（ＥＰＤ）、Ｘ射线双晶衍射以及透射电子显微镜方法,对ＣｄＴｅ缓冲层以及ＨｇＣｄＴｅ薄膜的位错密度、其纵向分布及与工艺条件的相关关系进行了评价、分析．研究发现退火可以有效地降低ＨｇＣｄＴｅ薄膜的位错密度．     

Application of nano-diffraction to local atomic distribution function analysis of amorphous materials

A method is proposed for the local atomic distribution function analysis of amorphous materials. This method is based on local halo-electron diffraction intensity analysis with nano-sized electron probes as small as 25 to approximately 3 nm, taking advantage of the intensity recording with imaging plate. Nanodiffraction and selected area electron diffraction (SAED) patterns from an amorphous SiNx (x approximately 4/3) thin film were taken using a conventional transmission electron microscope operated at 200 kV and recorded on imaging plates. An intensity correction to omit inelastic intensity was made using electron energy-loss spectroscopy. When a beam-convergence angle is larger than 1 x 10(-3) rad, the Wiener-filter deconvolution method becomes helpful in producing atomic pair distribution functions (PDFs) from the nano-diffraction intensity profiles that are more similar to the PDF from the SAED intensity. This technique was applied to the analysis of local amorphous structures of SiO2 layers formed by an oxygen-ion implantation into single crystal SiC.     

Synthesis and Properties of Mg-doped ZnO Nanobelts

The chemical vapor deposition(CVD)growth method is applicable to produce high-yield single-crystalline ZnO nanobelts.The Mg-doped ZnO nanobelts with a smooth surface have been successfully synthesized.The morphology,microstructure and optical properties of the ZnO nanobelts were analyzed by X-ray diffraction(XRD),scanning electron microscope(SEM),transmission electron microscope(TEM),selective area electron diffraction(SAED),energy dispersive X-ray spectroscopy(EDS)and photoluminescence(PL)spectroscopy.Resu...     

竹叶状ZnS纳米带的生成与表征

通过无催化物理热蒸发ZnS粉末的方法成功地制备了一种新颖的竹叶状ZnS纳米带。X射线衍射分析和扫描电镜透射电子显微镜,用来对ZnS生长物进行表征,检测显示,所制得的竹叶状纳米带的厚度50～100nm,度宽500～600nm,长度数十微米。透射电镜和选区电子衍射花样表明,制备的纳米带是单晶六角纤锌矿结构。样品的光学性能显示在424nm处有一个强烈的蓝光发射,这种发射是由于氧空位和其他表面态造成的。同时对纳米带的生长机制作了论述。     

Synthesis and photoluminescence properties of Mn-doped ZnS nanobelts

Mn-doped ZnS nanobelts have been prepared through a thermal evaporation method at 1100℃. The synthesized nanobelts are characterized with X-ray diffraction （XRD）, scanning electron microscopy （SEM）, selected area electron diffraction （SAED）, high-resolution transmission electron microscopy （HRTEM）, and photoluminescence （PL） spectroscopy. The results show that the nanobelts have an uniform single-crystal hexagonal wurtzite structure and grow along [0001 ] direction. Room-temperature photoluminescence reveals that the intrinsic PL of the nanobelts disappears and a new PL peak of the Mn-doped ZnS nanobelts emerges at 575 nm.     

Synthesis and Raman spectra of hammer-shaped ZnO nanostructures via thermal evaporation growth

Hammer-shaped ZnO nanostructures were synthesized on silicon substrate via a simple thermal evaporation process without catalysts or additives. Scanning electron microscopy results shows that ordered ZnO nanohammers grow from the Si substrate. Transmission electron microscopy and selected area electron diffraction analysis indicate that a single nanohammer is a single crystal and grows along (0001) direction. X-ray diffraction patterns for prepared samples are consistent with a wurtzite ZnO structure. The effect of temperature on Raman scattering of single crystal ZnO nanohammers in the temperature range from 83 to 523 K was determined. Temperature-dependent Raman spectra of E₂(high frequency or hf) exhibit phonon frequency redshift and linewidth broadening with increasing temperature, which can be explained by a model taking into account contributions of thermal expansion and anharmonic phonon processes. Results show that decay into three phonons is the probable channel for the E₂(hf) mode.     

控制定向聚集水热合成制备多种形貌的纳米钛酸锶

通过聚乙烯醇（PVA）辅助的水热合成方法制备出了纳米钛酸锶（SrTiO3）材料。X射线衍射（XRD）证明其结构为立方钙钛矿结构;透射电子显微镜（TEM）观察显示通过控制原料中锶和钛的浓度可以控制合成出具有花状纳米结构、纳米线及纳米线网状结构形貌的纳米SrTiO3材料。选区电子衍射（SAED）和高分辨透射电镜（HRTEM）证明不同形貌的纳米SrTiO3为类单晶结构。研究结果表明反应物中锶和钛的浓度是控制定向聚集合成不同形貌纳米SrTiO3结构的主要因素。     

Contrast enhancement in the phase plate transmission electron microscopy using an objective lens with a long focal length

A new optical condition using an objective lens (OL) of a long focal length (objective mini lens: OM) was tested to enhance image contrast in phase plate transmission electron microscopy (P-TEM). A phase plate was set on the selected area aperture plane where diffraction patterns were formed under the optical condition using the OM. A phase shift by the phase plate was added to the electron waves to visualize phase objects. The application of the OM to the P-TEM should provide higher phase contrast than that obtained by the OL for the phase objects. One of the reasons for the contrast enhancement is that high-angle scattering electron waves which would give the background intensity were not used for image formation due to the large spherical aberration. Another reason is that the cut-on frequency above which the phase shift was added by the phase plate could be smaller using the OL with a long focal length. Experimental results and model calculations showed the contrast enhancement of the biological specimens using the OM.     

纳米晶Pd─Si薄膜析出相的TEM研究

本文利用ＴＥＭ原位加热手段和选区电子衍射分析方法，对纳米晶Ｐｄ－Ｓｉ薄膜在加热过程中析出的相进行了研究。真空蒸发Ｐｄ＿（８０）Ｓｉ＿（２０）合金而得到的纳米晶Ｐｄ－Ｓｉ薄膜，其晶粒尺寸为１０ｎｍ，结构属ｆｃｃ。随着温度的升高，薄膜中晶粒长大，在局部区域有其它相析出。利用选区电子衍射图确定了这些析出相的结构。     

Charge： Glowing in the Dark

Many areas of structure analysis have focused on finding the locations of the atoms. If, instead of the atoms, we knew the positions of the electrons we would in fact know much more, and in most respects knowing where the nuclei are is not important. There is a long history of measurements using precise electron diffraction or X-ray diffraction of the average charge density in materials, but extending beyond to local charge density is, as yet, an unexplored area.     

Characterization of MOVPE-grown (Al, In, Ga) N heterostructures by quantitative analytical electron microscopy

The low pressure metalorganic vapor phase epitaxy growth of wurzite (Al, In, Ga)N heterostructures on sapphire substrates is investigated by quantitative analytical scanning transmission electron microscopy techniques like atomic number (Z-) contrast imaging and convergent beam electron diffraction (CBED). Especially (In, Ga)N quantum wells of different thicknesses as well as superlattices were analyzed with respect to defects, chemical composition variations, interface abruptness and strain (relaxation) effects. The interfaces in In_0.12Ga_0.88N/GaN quantum wells appear to be asymmetric. Additionally, we found composition variations of Δx_In≥0.03 within the InGaN quantum wells. The application of electron diffraction techniques (CBED) yields quantitative information on strain and relaxation effects. For the case of 17 nm thick InGaN quantum wells, we observed relaxation effects which are not present in the investigated thin quantum wells of 2 nm thickness. The experimentally obtained diffraction patterns were compared to simulations in order to get values for strain within the quantum wells. Additionally, the influence of dislocations on the digression of superlattices is investigated.