Stress related effects of GaN based semiconductor heterostructures

GaN基半导体作为光电子材料领域极为重要的材料，其异质结构在器件开发领域得到十分广泛的应用，目前，影响其未来发展的有几大关键性难题，本质上都与应力场有关，深受大家关注且亟待解决。本论文通过实验研究和计算模拟，全面深入地考察了GaN基半导体异质结构中应力场的相关效应，分析其复杂性质、阐明其物理机制，进而讨论这些效应对GaN基半导体电学和光学性质的作用。在基础研究手段上，我们利用金属有机物化学汽相外延技术制备GaN基异质结构，如侧向外延GaN和AlGaN/GaN系统的异质结构；采用包括电子显微镜、俄歇电子能谱、阴极荧光光谱等技术，表征异质结构的各项化学、物理性质。首先提出了电子信息的思想和“俄歇谱...GaN-based semiconductor has been one of the most important and potential optoelectronic materials，the heterostructure of which plays the dominant role in the fabrication of new functional devices. However, several critical problems that have significantly restricted the further development of its advanced applications are principally related to its stress field. The research in this thesis aimed t...学位：理学博士院系专业：物理与机电工程学院物理学系_凝聚态物理学号：B20022400

Defects in ⅢNitrides Epilayers

【中文摘要】 采用光荧光和阴极荧光方法 ,对 Ga N外延层中的黄色和蓝色发光进行测量分析 ;同时 ,采用原子力显微镜、扫描电镜及其能谱测量外延层中的缺陷。结果表明 ,黄色和蓝色发光与残留杂质有关。采用第一原理计算结果显示 ,残留 C、O杂质、本征缺陷等是黄色和蓝色的可能物理起源。采用原子力显微镜、扫描电镜、透射电镜及其能谱对 Ga N/Al Ga N异质结中的纳米管进行观测 ,了解了纳米管的形貌。结果表明 ,构成纳米管的小面可能是外延过程中表面吸附引起的 ;计算结果显示 ,纳米管形貌变化与 Ga N/Al Ga N界面处晶格失配应力有关。采用透射电镜观察外延层中沉积物及其周围位错的结构表明 ,沉积物附近应力的存在是位错产生的主要原因 【英文摘要】 Blue and yellow luminescence bands in undoped GaN epilayers were investigated and related to main residual C and O impurities by photoluminescence, which are suggested to be attributable to the electron transitions from O N states to V Ga states and between the inner levels of the C N O N complex, respectively, according to ab initio local density functional calculations. Larger nanopipes in undoped GaN/AlGaN hetero epilayers were imaged as dodecagonal pyramidal indentations, using atomic fo...国家重点基础研究发展规划项目 (批准号 :001CB610505 );国家自然科学基金 (批准号 :69976023、90206030、10134030 );福建省自然 科学基金 (批准号 :A0020001);教育部部分资助项

Abruptness Improvement of the Interfaces of AlGaN/GaN Superlattices by Cancelling Asymmetric Diffusion

973 program [2012CB619301, 2011CB925600]; "863" program [2011AA03A111]; FRFCU [2012121011, 2011121042]; National Natural Science Foundation [61204101, 61227009, 90921002]; Science and Technology Program of Fujian and Xiamen of ChinaInterfacial abruptness plays a critical role in affecting the quantum confinement effect in heterostructures. Here, we accurately determine the inter-diffusion depth across the AlGaN/GaN interfaces and propose a simple blocking scheme to effectively improve the superlattice abruptness. It is found that the Al diffusion depth at the upper and lower interfaces of the AlGaN barrier appears considerably asymmetric. Such difference leads to the gradient interfacial region and the asymmetric quantum well shape. A pair of ultra-thin blocking layers is introduced to the GaN/AlGaN interface to block the Al downward diffusion. After the blocking treatment, the interfacial abruptness is improved and the light emission intensity from the superlattice can be effectively enhanced. (C) 2013 The Japan Society of Applied Physic

The Dynamic and Kinetic Behavior of InN Growth on In-polar Surface

采用第一性原理模拟计算方法,从原子层面出发,了解Inn的生长动力学行为.通过计算n和In原子于不同覆盖度下In极性表面的TOP、H3以及T4位置上的形成能和扩散势垒,了解沉积原子的相互作用和成核.结果表明,In原子比n原子更容易在干净的In极性表面吸附、粘接,并通过扩散找到稳定位置,形成一个较致密的双In原子层.模拟计算了n和In原子在双In原子层和三In原子层表面的扩散,结果显示,在稳定的双In原子层上,n原子将通过垂直扩散穿过顶部In原子层,并在两In原子层表面之间横向扩散,形成纤锌矿结构的Inn材料;然而,In原子虽然可形成三In原子层或In滴,其上沉积的n原子也仅能垂直扩散穿过顶部In原子层,长成新的Inn分子层,与Inn基底间存在双In原子层或更厚的In薄膜,形成不完整的纤锌矿结构Inn薄膜.在此基础上,我们提出一新的Inn外延两步生长法,以在生长过程中尽量保持表面只存在双In原子层结构,为高质量Inn薄膜的外延提供理论依据.We try to understand the growth kinetic behavior of InN film at the the atomic level,using the first principles simulation method.By calculating the formation energies and barriers of N and In atoms at top,h3,and t4 site under different coverages,the interreaction and nucleation behaviors of the deposition atoms were known.The results showed that In atoms are more favourite to adsorb at a stable site on In polar surface by adhesion and diffusion,and form a compact In bilayer.Furthermore,the diffusion of N and In atoms were simulated on the In bilayer and trilayer.The results revealed that the N atoms will diffuse vertically into the top In layer of the stable In bilayer,and then form a wurtzite InN layer by lateral diffusion inside the In bilayer.Although an In trilayer or droplet can exist during the epitaxy,N atoms also can only penetrate into the top In layer,leading to a In bilayer or thick In film between deposited InN layer and the InN substrate,and an incomplete wurtzite InN film formed.On the basis of above results,we porpose a two-step growth method for InN epitaxy by keeping the In bilayer to achieve high quality InN film.国家重点基础研究发展计划(973)项目(2011CB925600;2012CB619301);国家自然科学基金项目(90921002;60827004;61076084

Electronic Structures of Zinc-Blende GaN (001) Surface

采用混合基表示的第一原理赝势方法 ,计算了闪锌矿结构的 Ga N(0 0 1) (1× 1)干净表面的电子结构 .分析了得到的各原子分态密度、面电荷密度分布以及表面能带结构等性质 ,比较了 Ga N(0 0 1)的 Ga端表面和 N端表面两种情况 .结果显示 ,闪锌矿 Ga N(0 0 1)的 Ga端表面比 N端表面更稳定 ,这两种 (1× 1)表面都是金属特性 .此外 ,还讨论了次表面层原子的性质国家高技术研究发展计划 ( 86 3-715 -0 10 -0 0 2 2 );; 国家自然科学基金( 6 9976 0 2 3);; 福建省自然科学基金( A0 0 2 0 0 1)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

Accurate Color Tuning of Firefly Chromophore by Modulation of Local Polarization Electrostatic Fields

Foundation for Science and Technology of Portugal [PTDC/FIS/73578/2006]Although many microenvironmental factors contribute to the color shift of light emission from the firefly chromophore, the dominant one is the local electrostatic field. This opens up the possibility of accurate color tuning the bioluminescent absorption and emission by adjusting the local charged residues. With this aim, the optical response of oxyluciferin for different electrostatic fields is computed by using time-dependent density-functional theory. We find that the wavelength shift is correlated to the projection of the electrostatic field on the molecular plane, and that the fluorescent intensity of the second excitation peak can be effectively enhanced or suppressed (+/- 30%) by field modulation. A model is formulated by correlating the shift in the spectral maxima with the projection of the local electrostatic field on the molecular plane. This method provides a predictable determination of the structural modifications leading to a particular color shift and/or fluorescent efficiency enhancement

Full Color Modulation of Firefly Luciferase through Engineering with Unified Stark Effect

973 program [2012CB619301, 2011CB925600]; "863" program [2011AA03A111]; FRFCU [2012121011, 2011121042]; NNSF of China [61204101]The firefly luciferase has been a unique marking tool used in various bioimaging techniques. Extensive color modulation is strongly required to meet special marking demands; however, intentional and accurate wavelength tuning has yet to be achieved. Here, we demonstrate that the color shift of the firefly chromophore (OxyLH(2)-1) by internal and external fields can be described as a unified Stark shift. Electrostatic microenvironmental effects on fluorescent spectroscopy are modeled in vacuo through effective electric fields by using time-dependent density functional theory. A complete visible fluorescence spectrum of firefly chromophore is depicted, which enables one to control the emission in a specific color. As an application, the widely observed pH-correlated color shift is proved to be associated with the local Stark field generated by the trace water ions (vicinal hydronium and hydroxide ions) at active sites close to the OxyLH(2)-1

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

Extraordinary N atom tunneling in formation of InN shell layer on GaN nanorod m-plane sidewall

We report the extraordinary tunneling process that finds the lower cohesive energy route for stablizing InN shell layer on m-plane sidewall of GaN nanorod. The [0001] orientated GaN nanorod array is grown on sapphire substrate patterned with Ga nanoparticle by metal-organic vapor deposition method, based on which the simulation structures of c-plane top surface and m-plane sidewall surface is constructed for the first-principles calculations. The results show that the introduction of In wetting monolayer could effectively lower the cohesive energy of adalayers on non-polar GaN surfaces. Most importantly, it is revealed that there exists an extraordinary tunneling process in which the N atoms will drag out the In wetting atoms and tunnel through to form stable InN shell layer on the nanorod sidewall