Study on the fitting model of AlN by ellipsometric spectroscopy

采用椭圆偏振光谱对MOCVD生长的AlN薄膜在波长430~850 nm的光学参数进行了测量.通过建立不同的物理和色散模型,分别考察了薄膜表面和界面的椭偏效应.拟合结果表明,AlN薄膜的物理模型在引入表面层后,两类色散模型拟合的数据均与椭偏光谱实验数据吻合得很好.进一步考虑界面层所拟合的结果显示,界面层对Lorentz色散模型的影响较小,并且,其拟合所得AlN薄膜厚度与扫描电镜所测厚度一致,因此,认为仅含表面层的Lorentz色散模型更简单实用.The optical parameters of AlN film,which was grown by MOCVD system,were measured by spectroscopic ellipsometry in the wavelength range of 430~850nm.Through the establishment of different physical and dispersion models,The effects of the surface and interface on spectroscopic ellipsometry were inspected.The results indicate that after the introduction of surface,the fitting data of two dispersion model all have a good agreement with the SE experimental data.Further results of considering the interface layer show that the effect of interface layer for Lorentz dispersion model is smaller,and,the fitting thickness of AlN film is consistent with the SEM result.Therefore,the Lorentz dispersion model with only surface layer is more simple and practical for AlN film.“863”计划资助项目(2006AA03A110);; 基础科研资助项目(A1420060155);; 国家自然科学基金资助项目(60336020);; 厦门市科技计划资助项目(3502Z20063001

The optical constants of GaN film investigated by spectroscopic ellipsometry

采用椭圆偏振光谱法,在1.5~6.5 eV光谱范围研究了纤锌矿结构GaN外延薄膜.通过物理模型建立和光谱拟合得到了GaN外延薄膜的厚度和光学常数.所得厚度值与扫描电子显微镜测量的结果相差仅为0.4%.表明所采用的模型和Cauchy吸收色散表式适用于GaN薄膜.进一步采用四相逐点拟合算法得到更全面更准确的GaN薄膜光学常数.A wurtzite GaN thin film was investigated by spectroscopic ellipsometry(SE) in the spectrum range of 1.5~6.5eV.The thickness and optical constants were obtained by building physical structure model and spectral fitting.The difference of the thickness obtained by SE and by scanning electron microscope(SEM) is only 0.4%,which shows that the model and Cauchy absorbent formula are suitable to study the properties of GaN.Furthermore,the four-phase point-by-point fitting model was used to obtain the optical constants in more accuracy.“863”计划资助项目(2006AA03A110);; 基础科研资助项目(A1420060155);; 国家自然科学基金资助项目(60336020);; 厦门市科技计划资助项目(3502Z20063001

Numerical Solution of the Space Fractional Differential Equation

考虑空间分数阶微分方程(即在一个标准的扩散-对流方程中,用分数阶导数代替空间二阶导数),给出了该分数阶微分方程的显式和隐式有限差分格式。并证明了显式格式条件稳定和条件收敛,而隐式格式则是无条件稳定和无条件收敛。In this paper,a space fractional differential equation is considered.The equation is obtained from the advection-diffusion equation by replacing the second order derivative in space by a fractional derivative in space of order.The finite difference approximation for this equation is presented.The stability and convergence of the finite difference approximation are analyzed.国家自然科学基金资助项目(10271098

High Al Content AlGaN Based LED Functional Structures

采用金属有机物气相外延(MOVPE)技术在C面蓝宝石衬底上,引入脉冲原子层外延技术,制备了一系列表面平整度较高的高Al组分AlgAn基异质结构外延片.并采用电子束金属蒸镀技术及优化热退火方法,获得了良好的欧姆接触电极,进一步将外延片制备成lEd管芯.通过对量子结构有源层量子阱混晶组分的设计和调整,掌握并实现了主波长260~330nM紫外lEd结构材料的制备.High Al content AlGaN-based ultraviolet light-emitting diode(LED) structures were grown on sapphire substrate by metal organic vapor-phase epitaxy(MOVPE).The pulsed atomic layer epitaxy technology was adopted to improve the crystal quality.Ohmic contacts for the LED devices were obtained by optimizing the annealing conditions.The UV-LEDs with different wavelength(from 260 nm to 330 nm) were achieved by tuning the Al content.国家自然科学基金项目(60827004;90921002);国家重点基础研究发展计划(973)项目(2011CB301905

X-ray reflectivity and atomic force microscopy studies of MOCVD grown AlxGa1-xN/GaN superlattice structures

The grazing incidence X-ray reflectivity (GIXR) technique and atomic force microscopy (AFM) were exploited to obtain an accurate evaluation of the surfaces and interfaces for metalorganic chemical vapor deposition grown Al xGa1-xN/GaN superlattice structures. The X-ray diffraction results have been combined with reflectivity data to evaluate the layer thickness and Al mole fraction in the AlGaN layer. The presence of a smooth interface is responsible for the observation of intensity oscillation in GIXR, which is well correlated to step flow observation in AFM images of the surface. The structure with a low Al mole fraction (x = 0.25) and thin well width has a rather smooth surface for the Rrms of AFM data value is 0.45 nm. ? 2011 Chinese Institute of Electronics

Development of high Al content structural Ⅲ nitrides and their applications in deep UV-LED

随着高gA组分Ⅲ族氮化物相关研究的日趋深入和生长技术的日益成熟,人们逐渐将研究重心转向具有更宽带隙的高Al组分Ⅲ族氮化物。该材料常温下带隙宽至6.2 EV,可覆盖短至210 nM的深紫外波长范围,具有耐高温、抗辐射、波长易调控等独特优点,因而是制备紫外发光器件的理想材料。目前,高Al组分Ⅲ族氮化物材料质量不高,所制备的深紫外lEd发光器件仍存在内量子效率、载流子注入效率和沿C轴方向正面出光效率较低的难题,因而制约了高效紫外发光器件的制备。本文着重介绍了近年来在高Al组分Ⅲ族氮化物生长动力学方面的研究进展,总结和梳理了量子结构设计、内电场调控以及晶体场调控等方面的相关研究,以期实现高质量深紫外lEd的制备。Along with the extensive investigations and growth technology maturation on high Ga content III-nitrides,researchers have moved their focus onto high Al content III-nitrides.Given a wider band gap up to 6.2 eV at room temperature,covering UV-light area as short as 210 nm,as well as other advantages of III-nitrides,high Al content III-nitrides are ideal materials for the fabrication of UV-light emitting devices.At present,there are certain challenges in the fabrication of UV-light emitting devices with high internal quantum efficiency,carrier injection efficiency and light-extraction efficiency due to the low quality materials.In this work,the progress on growth kinetics of high Al content III-nitrides in recent years has been reviewed comprehensively,and the corresponding researches in quantum structure design,internal electric field modification and crystalline field modification have been overviewed and analyzed.This review is expected to be informative for the fabrication of deep UV-LEDs.“973”规划项目(2012CB619301、2011CB25600); “863”计划项目(2011AA03A111); 国家自然科学基金项目(61227009、90921002); 中央高校基本科研业务费专项资金资助项目(2012121014、CXB2011029); 福建省自然科学基金计划项目(2012J01024