GaN／Al2O3（0001）的匹配机制及氮化的作用

在Al2O3(0001）衬底上用MOCDVD方法进行了GaN的外延生长，通过X射线衍射（同步辐射源）研究了GaN和Al2O3(0001）的匹配关系。结果表明，经充分氮化的衬底上，GaN以单一的匹配方式沿[0001]方向生长：在Al2O3(0001）衬底未经氮化或氮化不充分时，不同程度地出现了其它三种绕<11-20>晶带轴倾斜一定角度的匹配位向。指出了GaN/Al2O3(0001）的几种匹配方式的晶体学规律。GaN绕<11-20>晶带轴倾斜的匹配方式是其外延生长过程中降低和Al2O3(0001）的晶格失配、释放界面应变的重要机制之一。     

带有AlN插入层的GaN薄膜的结构及应变研究

利用金属有机化学汽相沉积（MOCVD）法在硅衬底上生长具有AlN插入层的GaN外延膜，采用高分辨X射线衍射（HRXRD）和卢瑟福背散射/沟道（RBS/Channeling）技术研究分析其结构和应变性质。从RBS<0001>沟道谱可知，该外延膜具有良好的结晶品质，χ_min=2.5%。利用不同方位角上XRD摇摆曲线测量，可得出GaN（0001）面与Si（111）面之间的夹角β=1.379°。通过对GaN（0002）和GaN（1015）衍射面的θ-2θ扫描，可以得出GaN外延膜在垂直方向和水平方向的平均弹性应变分别为-0.10%±0.02%和0.69%±0.09%。通过对{1010}面内非对称<1213>轴RBS角扫描可得出由弹性应变引起的四方畸变e_T在近表面处为0.35%±0.02%。外延膜弹性性质表明GaN膜在水平方向具有张应力(e∥>0)、在垂直方向具有压应力(e^⊥<0)，印证了XRD的结果。四方畸变是深度敏感的，通过对不同深度的四方畸变计算可知，AlN插入层下面的GaN外延膜弹性应变释放速度比AlN层上面的GaN层弹性应变释放快，说明AlN层的插入缓解了应变释放速度。     

硅上异质外延氧化铝的X射线测试分析

高剂量X射线粉末衍射测试说明升高温度有利于γ－Al2O3/Si外延生长，单晶衍射法证明应用低压CVD和高真空外延技术在我们的实验室生长出γ－Al2O3/Siuj单晶薄膜。它们的结晶关系是（100）γ－Al2O3/／Si，[010]γ－Al2O3//[010]Si。     

AlGaN/GaN异质结构的X射线衍射研究

在(0001)取向的蓝宝石(α-A12O3)基片上用金属有机物化学气相沉积(MOCVD)方法生长了势垒层厚度为1000A的Al0．22Ga0．78N／GaN异质结构,利用高分辨X射线衍射(HRXRD)技术测量了样品的对称反射(0002)和非对称反射(1014)的倒易空间Mapping(RSM)。结果表明,样品势垒层的内部微结构与应变状态和下层i-GaN的微结构与应变状态互相关联。样品势垒层的微应变已经发生弛豫,而且具有一种“非常规”应变弛豫状态,这种弛豫状态的来源可能与n-AIGaN的内部缺陷以及i-GaN／α-Al2O3界面应变弛豫状态有关。掠入射X射线衍射研究表明样品内部的应变是不均匀的,由表层的横向压应变状态过渡到下层的张应变状态,与根据倒易空间Mapping分析得到的结果一致。     

立方相GaN外延层的X射线四圆衍射分析

本采用多功能四圆X射线衍射仪测绘出立方相GaN/GaAs(001）外延层的极图和倒易空间mapping，研究了六角相GaN和立方相微孪晶的取向、晶粒形状和极性等特征。结果表明外延层中片状六角相与立方相之间的取向关系为：（111）／／（0001）、＜112＞／／＜1010＞。由于（111）Ga面的外延速度远高于{111}N面，导致较多六角相和立方相微孪晶在[110]或[110]方向上的（111）Ga面和(111)Ga面上形成，而在[110]或[110]方向上六角相和立方相微孪晶含量较低。外延层中立方相微孪晶的含量明显低于六角相，表明六角相的形成可以更有效的释放局部应力集中。     

GaN核辐射探测器材料与器件研究进展

文章介绍GaN材料作为核探测器的潜在优势和国内外的研究状况，并概要综述GaN材料外延的主要技术、特点及其最新发展。通过模拟计算，总结了使用GaN制备核探测器对材料的基本要求。同时，根据目前的研究现状，提出了在GaN材料生长和器件制作方面存在的主要技术问题及其解决方向。     

中频磁控溅射制备GaN薄膜

采用中频磁控溅射技术,以金属Ga为靶材料,在si(111)衬底上形成了GaN薄膜,研究了溅射压强、衬底温度等对GaN薄膜结构和成分的影响.发现沉积气压为0.4～1.0 Pa时,薄膜呈GaN(002)取向,气压大于1.0 Pa和小于0.4 Pa时,用X射线衍射方法难以观察到GaN(002)的衍射峰.X射线能谱分析表明在最佳实验条件下制备的GaN薄膜的元素比Ga∶N为1∶1.     

分子束外延生长ZnO薄膜的XAFS研究

利用同步辐射广延X射线吸收精细结构(EXAFS),研究在不同条件下分子束外延制备的ZnO薄膜,如分别在蓝宝石(0001)、Si(100)衬底上,生长温度为200℃或300℃下得到样品的局域结构。发现这些ZnO薄膜的EXAFS函数(k^2x(k))谱形状相似,说明各个样品都具有较为相近的基本局域结构。对生长温度为200℃的ZnO／Al2O3(0001)和ZnO／Si(100)样品,其Zn-O第一配位峰的无序度仃。分别为0．0054A^2和0．0080A^2,当生长温度从200℃提高到300℃时,ZnO／Al2O3(0001)样品的Zn-O第一配位峰的无序度仃。降为0．0039A^2。结果表明衬底与ZnO的晶格失配度和生长温度对ZnO薄膜的配位数、Zn-O键长影响不大,但较小的晶格失配度和较高的生长温度下得到的ZnO薄膜局域有序性较高;且样品的局域结构越有序,相应的配位峰幅度也越高。     

分子束外延生长ZnO薄膜及性能研究

用分子束外延（MBE）和氧气氛方法，并改变束源炉和衬底生长温度，在Si(100)衬底上，采用Zn作缓冲层以解决ZnO层与衬底间的晶格失配问题，生长得到ZnO薄膜。在ZnO/Zn/Si(100)薄膜样品的X射线衍射（XRD）谱中，观测到ZnO的（100）、（200）、（101）和（103）等衍射峰；用原子力显微镜（AFM）观测ZnO薄膜的表面形貌，为直径约80－90mm的量子点，表明已得到具有纳米结构的ZnO薄膜。用同步辐射EXAFS技术研究了ZnO薄膜的局域结构，得到有关的几个结构参数。     

NSRL在半导体表面结构的光电子衍射研究

利用角分辨光电发射精细结构(ARPEFS)技术研究了GaAs(001)面,验证了Biegelsen提出的钙双层模型的正确性。拟合结果显示,最外层构成二聚体的两个钙原子沿[110]方向移动聚拢,偏离体材料格位8.3%。同时最外层的钙原子向内收缩2.1%。利用X射线光电子衍射(XPD)实验技术研究了硫钝化方法处理过的GaAs(001)表面结构,确定了钝化的硫原子位于第一层钙原子的桥位上。与钙原子成键的键长为3.62?、键角为61.2°。使用与能量和角度有关的光电子衍射技术并结合多重散射团簇模型计算对Al2O3衬底上生长的GaN单晶薄膜表面的极化性质进行了研究,确定了该GaN表面极性为钙在最外层的正极化性。     

Investigations on the effect of 100 MeV Ni ions irradiated chloride vapour phase epitaxy (Cl-VPE) grown GaN epilayers

Gallium nitride (GaN) epilayers have been grown by chloride vapour phase epitaxy (Cl-VPE) technique and the grown GaN layers were irradiated with 100 MeV Ni ions at the fluences of 5 × 10¹² and 2 × 10¹³ ions/cm². The pristine and 100 MeV Ni ions irradiated GaN samples were characterized using X-ray diffraction (XRD), UV-visible transmittance spectrum, photoluminescence (PL) and atomic force microscopy (AFM) analysis. XRD results indicate the presence of gallium oxide phases after Ni ion irradiation, increase in the FWHM and decrease in the intensity of the GaN (0 0 0 2) peak with increasing ion fluences. The UV-visible transmittance spectrum and PL measurements show decrease in the band gap value after irradiation. AFM images show the nanocluster formation upon irradiation and the roughness value of GaN increases with increasing ion fluences.     

Structural and optical study of irradiation effect in GaN epilayers induced by 308 MeV Xe ions

Wurtzite GaN epilayers irradiated at room temperature with 308 MeV ¹²⁹Xe³⁵⁺ ions to fluences of 1 × 10¹³ and 3 × 10¹³ cm⁻² have been studied by contact mode atomic force microscopy (AFM), high-resolution X-ray diffraction (HRXRD), micro-Raman scattering and photoluminescence (PL) spectroscopy. The AFM images showed that the surface of GaN films was etched efficiently due to the Xe ion irradiation. The initial step-terrace structure on GaN surface was eliminated completely at a fluence of 3 × 10¹³ cm⁻². HRXRD and Raman results indicated that the Xe ion irradiation led to a homogenous lattice expansion throughout the entire ∼3 μm-thick GaN films. The lattice expansion as well as the biaxial compressive stress of the films was increasing with the increase of ion fluence. PL measurements showed that a dominant yellow luminescence band in the as-grown GaN films disappeared, but a blue and a green luminescence bands were produced after irradiation. Based on these results, the strong electronic excitation effect of 308 MeV Xe ions in GaN is discussed.     

Swelling or erosion on the surface of patterned GaN damaged by heavy ion implantation

Wurtzite undoped GaN epilayers (0 0 0 1) was implanted with 500 keV Au⁺ ions at room temperature under different doses, respectively. Ion implantation was performed through photoresist masks on GaN to produce alternating strips. The experimental results showed that the step height of swelling and decomposition in implanted GaN depended on ion dose and annealing temperature, i.e., damage level and its evolution. This damage evolution is contributed to implantation-induced defect production, and defect migration/accumulation occurred at different levels of displacement per atom. The results suggest that the swelling is due to the formation of porous structures in the amorphous region of implanted GaN. The decomposition of implanted area can be attributed to the disorder saturation and the diffusion of surface amorphous layer.     

中国先进研究堆中子织构谱仪的分辨率和极图窗研究

为计算中国先进研究堆（CARR）中子织构谱仪的分辨率和极图窗,基于倒空间衍射几何的误差分析推导了谱仪分辨率和极图窗的计算公式,并将其应用于CARR中子织构谱仪。结果表明,极图窗近似为狭窄的长方形,其沿β方向的分辨率较高,沿α方向的分辨率随衍射角变化较大。对于特定的衍射角,³He管点探测器的α分辨率为固定值,而二维位置灵敏探测器的α分辨率可根据样品和织构分布的测量需要沿纵向进行分份调整。     

Strain in GaN／Si〈111〉by RBS／Channeling

GaN film grown on Si substrate was characterized by Rutherford backscattering /Channeling(RBS/C).The experimental results show that the thickness of GaN epilayer is about 2.5μm and the GaN film has a good crystalline quality (Xmin=3.3%).By using channeling angular scanning,the 0.35% of average tetragonal distortion in GaN layer is observed.I addition,the depth profiles of strain in GaN film layer reveal that the strain in GaN film nonlinearly decreases with the increase of film thickness,The strain-free thickness(above 2.5μm) of GaN film on Si substrate is far below that(150μm) of GaN film on Sapphire.     

RBS analysis of InGaN/GaN quantum wells for hybrid structures with efficient Förster coupling

There is strong current interest in Förster resonant energy transfer (FRET) from a semiconductor quantum well (QW) to an overlayer of another luminescent material. The FRET process becomes efficient when the two materials are placed at interaction distance of a few nanometres. The additional requirement of large spectral overlap between the energy donor and acceptor can be satisfied by combinations of InGaN/GaN QWs (as donors) and overlayers of either light-emitting polymers or nanocrystalline semiconductor quantum dots (as acceptors), both of which can be tailored to have high absorption in the QW emission region. Here we study a set of custom grown InGaN/GaN single QW samples, in which the GaN cap layer thickness was varied to modulate the FRET rate in hybrid structures. We used high-resolution grazing angle RBS experiments to determine the GaN cap layer thickness, varied from 2 to 12 nm, which controlled the interaction distance between the QW and the coupled luminescent medium in hybrid structures. The very careful experiments and data analysis are discussed in detail, including a consideration of the errors in the final results obtained. An example of the use of the measured thickness values to confirm the dominance of sheet-to-sheet dipole-dipole interactions in QW-polymer hybrid structures is discussed.     

Yellow and red luminescence in Mg-implanted GaN epitaxial films

X-ray diffraction (XRD), attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) and photoluminescence (PL) were applied to study yellow and red luminescence properties of as-grown and Mg-implanted n-type wurtzite GaN films grown on sapphire substrates by metal-organic chemical vapor deposition. The influence of different Mg-implanted fluences on yellow and red luminescence was studied. The as-grown GaN thin films exhibited intense broad yellow emission which reduces drastically after Mg ion implantation. A red luminescence band at approximately 750 nm appears when the Mg implantation fluence is low (10¹³ cm⁻²) whereas a yellow luminescence band suddenly increases at a Mg-implanted fluence of 10¹⁶ cm⁻². The possible reasons of these phenomena are discussed.     

High resolution TEM of high burnup UO2 fuel

High-resolution TEM (HRTEM) observations and nano-area EDX analyses were carried out on small intragranular bubbles in the outer region of high burnup UO₂ pellets. Sample was prepered from the outer region of UO₂ pellet, which had been irradiated to the pellet average burnups of 49 GWd/t in a BWR. HRTEM observations and element analyses were made with a 200 KV cold-type field emission TEM (Hitachi FE-2000) having an ultra-thin window EDX (Noran Voyager). Lattice image and nano-area EDX results indicate the presence of 4-8 nm size Xe-Kr bubbles along with fission products of five metal particles, Mo-Tc-Ru-Rh-Pd. Nano-diffraction patterns from bubbles show two different new patterns besides matrix UO₂. From the Xe/U proportion obtained by nano-area EDX peak and nano-diffraction patterns from bubbles, it was concluded that Xe in the small bubbles was present in a solid or near solid state at very high pressure. Furthermore, from the results of high resolution images and diffractions obtained from recrystallized grains in rim structure region, neighboring recrystallized grains were clarified to be present with high angle grain boundaries.