Modification of polarization field in III-nitride semiconductors

III族氮化物半导体在短波长高亮度发光二极管、高功率激光器、高灵敏度光探测器、以及高温大功率电子器件等方面有着广泛的应用前景。不同于传统的III-V族化合物半导体，纤锌矿结构的III族氮化物半导体具有极强的自发极化和压电极化效应。极化效应在III族氮化物的应用中起着双刃的作用，既有其危害处也有其得利处。对III族氮化物半导体中的极化场加以调控，避其短扬其长，是人们渴望深入了解的课题。本论文围绕III族氮化物半导体的极化效应和极化场调控，结合第一性原理计算方法、MOVPE生长技术、材料的结构和性能测试，着重从理论设计和MOVPE外延生长两方面开展了系统的研究，主要取得如下研究成果：首次提出并构建...III-nitride semiconductors are very promising materials for their applications in optoelectronic devices (both emitters and detectors) and high power/temperature electronic devices. Being non-centro-symmetric and high degree ionicity, wurtzite III-nitrides exhibit strong spontaneous and piezoelectric polarization effects, which influence carrier distributions, electric fields, and consequently a w...学位：工学博士院系专业：物理与机电工程学院物理学系_微电子学与固体电子学学号：B20042401

Emission Mechanism of High Al-content AlGaN Multiple Quantum Wells

紫外LED的发光功率和效率还远不能令人们满意,波长短于300 nm的深紫外LED的发光效率普遍较低。厘清高Al组分Al Ga N多量子阱结构的发光机制将有利于探索改善深紫外LED的发光效率的新途径、新方法。为此,本文通过金属有机气相外延技术外延生长了表面平整、界面清晰可辨且陡峭的高Al组分AlGa N多量子阱结构材料,并对其进行变温光致发光谱测试,结合数值计算,深入探讨了Al Ga N量子阱的发光机制。研究表明,量子阱中具有很强的局域化效应,其发光和局域激子的跳跃息息相关,而发光的猝灭则与局域激子的解局域以及位错引起的非辐射复合有关。The quantum efficiency of deep UV light emitting diodes( LED) drops dramatically with the increasing of Al content. Understanding the emission mechanism of high Al-content Al Ga N multiple quantum wells( MQW) is the one of the most important objects for improving the quantum efficiency of deep UV LED. In this work,high Al-content Al Ga N MQW structure with atomically flat hetero-interfaces was grown and characterized by photoluminescence( PL) measurements at different temperatures. The results indicate that there is a strong exciton-localization effect in the MQW structure and the emission is closely related to the hopping of the excitons. Due to the exciton delocalization and nonradiative recombination at defects,the PL intensity is strongly quenched at high temperatures.“973”国家重点基础研究发展计划(2012CB619300);; “863”国家高技术研究发展计划(2014AA032608);; 国家自然科学基金(U1405253;61227009;11204254;11404271);; 福建省自然科学基金(2015J01028)资助项

DEVELOPMENT OF NANO-SCALE CHARACTERIZATIN TECHNIQUES BY AUGER ELECTRON SPECTROSCOPY

随着纳米结构材料的广泛应用,新型微纳尺度表征技术成为纳米科学技术发展的重要途径。本文基于局域电子信息全面性的思想,从俄歇电子能谱的原理出发,理论推导出俄歇价电子能谱的简明表述方式,确定俄歇价电子能谱与微观电子结构信息的内在联系和物理意义,建立了俄歇电子能谱探测微区一系列宏观参量的新技术。其中应力测量技术的空间分辨率可优于20nm,为微纳尺度力学测量的发展提供了重要的方法;非接触性的局域电学性质测量技术,超越了传统电学测量方法的思想框架,实现了无外场驱动的电荷密度分布、电场分布等本征电学性质表征、以及半导体异质结构整个空间区域的能带构造;结构相的测定技术,使纳米微区材料的晶体结构相识别成为可能;半导体微区导电类型测定技术,延续了非接触性电学测量的优点,并且能够灵活地探测分析复杂光电器件结构中不同区域的导电类型分布。通过实际应用于侧向外延GaN不同区域、AlxGa1-xN/GaN超晶格量子阱结构、ZnO纳米颗粒等纳米尺度复杂体系的微区宏观性质探测,获得应力/应变、电荷密度/电场、结构相以及导电类型及其分布等结果,验证了所建立的测量技术的有效性和可靠性。Inspired by the rapid progresses and wide applications of nanostructured materials,novel nano-scale characterization techniques have attract much attention in nanoscience.Based on the concept of full information of local electron,we initiate with the principle of Auger electron spectrum,simplify the theoretical expression spectrum,reveal the intrinsic relationship between the valence-band Auger electron spectrum and the microscopic electronic structures,and develop a couple of novel nano-scale detection techniques for several important physical parameters.1) A technique for local strain measurement is achieved with a spatial resolution better 20nm,which provides an effective method for the investigations of mechanical properties in nano-scale;2) A non-contact probing of local charge and electric field exempts from the influence of external field and enables construction of energy band for semiconductor heterostructures,which is beyond the conventional frame of electrical measurement;3) A technique for structural phase identification is developed to distinguish local structures in nano-structural materials;4) A technique for determination of conductivity type in semiconductor is able to apply to the local type detection in complex structures of optoelectronic devices.Practical applications of these novel techniques have been carried out on nano and complex structures,such as epitaxial-lateral-overgrowth GaN,AlxGa1-xN/GaN superlattice,ZnO nanoparticle,and so on.A series of precise results and interesting phenomena about strain,charge concentration,electric field,structural phase,conductivity type,and their distributions have been obtained in these structures,which provided an objective evaluation for the solidity and effectiveness of these techniques

Design of Vertical AlGaN-based Ultraviolet LEDs with Distributed Bragg Reflectors-pixed Metal Combined Electrodes

AlgAn基紫外lEdS具有高光子能量和短波长的特点,在诸多领域有着广阔应用前景.结合器件电流分布、温度控制及出光增强等多物理场因素,采用有限元方法设计了一种分布式布拉格反射与小面积金属接触复合三维电极结构的AlgAn基紫外lEdS.计算分析表明,相比于传统垂直结构器件,该器件结构具有高效的电流注入效率、良好的散热水平及较高的出光效率,有望大幅度提高紫外发光器件的光电转换效率.AlGaN-based ultraviolet light-emitting diodes(UV LEDs)enjoy enormous potential for a wide range of applications.However,the efficiency of UV LEDs remains low.In this work,a novel vertical structure with distributed bragg reflectors-pixel metal combined electrodes was designed to improve the performance of ultraviolet LEDs,by utilizing the coupling relationship of multiphysics:current distribution,temperature control,and light extraction.Numerical analysis results indicate that the current distribution,heat dissipation,and light extraction efficiency in such structures are much better than those in the traditional vertical structure UV LED devices.As a result,the output power is expected to be improved by 204%and 664%at the injection current of 20 mA and100mA,respectively.国家重点基础研究发展计划(973计划)(2012CB619301;2011CB25600); 国家高技术研究发展计划(863计划)(2014AA032608); 国家自然科学基金(U1405253;61227009;11204254;11404271

Ethanol assisted formation of aligned MWCNT bundles on nanostructured ZnO surface

In this Letter ZnO surface was used to separate the well-aligned MWCNT bundles from solution phase. This procedure is based on the etching effect of ethanol on the side wall of MWCNTs. Under proper treating temperature, MWCNT bundles might form and suspend in acetonitrile due to the ethanol induced appropriate roughening of the ektexine of the MWCNTs. Among such formed MWCNT bundles, well aligned ones of particular size extracted from the solution phase by their entropy driven selective adsorption on nanostructured ZnO surface of proper morphology. High resolution images by scanning electron microscopy validated these processes. ? 2014 Published by Elsevier B.V

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

The inn epitaxy via controlling in bilayer

The method of In bilayer pre-deposition and penetrated nitridation had been proposed, which had been proven to have many advantages theoretically. To study the growth behavior of this method experimentally, various pulse times of trimethylindium supply were used to get the optimal indium bilayer controlling by metalorganic vapour phase epitaxy. The results revealed that the InN film quality became better as the thickness of the top indium atomic layers was close to bilayer. A following tuning of nitridation process enhanced the quality of InN film further, which means that a moderate, stable, and slow nitridation process by NH3 flow also plays the key role in growing better-quality InN film. Meanwhile, the biaxial strain of InN film was gradually relaxing when the flatness was increasingly improved. ? 2014 Zhou et al.; licensee Springer

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

High Mg effective incorporation in Al-rich AlxGa1-xN by periodic repetition of ultimate V/III ratio conditions

According to first-principles calculations, the solubility of Mg as a substitute for Ga or Al in AlxGa1-XN bulk is limited by large, positive formation enthalpies. In contrast to the bulk case, the formation enthalpies become negative on ALxGa1-xN surface. In addition, the N-rich growth atmosphere can also be favorable to Mg incorporation on the surface by changing the chemical potentials. On the basis of these special features, we proposed a modified surface engineering technique that applies periodical interruptions under an ultimate V/III ratio condition (extremely N-rich), to enhance Mg effective incorporation. By optimizing the interruption conditions (2 nm interruption interval with 2 s interruption time), the enhancement ratio can be up to about 5 in the Al0.99Ga0.01N epilayer. ? 2014 Zheng et al