【作者】 王泽岩；

【导师】 黄柏标；

【作者基本信息】 山东大学 ， 材料物理与化学， 2009， 博士

【摘要】 材料科学的发展是人类文明发展的标志,从人类诞生到现在先后经历了石器时代、青铜时代、铁器时代,而现在人们进入了以半导体材料为基础的电子信息时代。随着科学技术的飞速发展和人类文明的不断进步,人们对材料应用与需求标准越来越高,目前传统的半导体材料已经渐渐不能满足人们的需要,探索和研究具有更好性能的新材料成为材料科学发展的重点。宽禁带半导体材料是一种具有优良性质,能够应用于制作大功率、高温、高频器件,并且能够实现更高集成度的半导体材料,是人类社会在未来一段时间内最具应用前景和研究意义的材料之一。而伴随着上世纪80年代,纳米技术与纳米材料的出现,人们发现材料的性能不仅仅取决于材料本身的化学组分,还与其微观结构与聚集状态密切相关。材料的微观结构及其聚集状态又受到材料的制备过程、制备工艺的影响。因此,对材料的生长过程、形貌、结构等宏观参数进行微结构调控,通过研究这些宏观参数对材料本身的原子结构、电子分布等微观参数的影响,从而改进材料的物理性能,对材料科学的发展以及材料在实际生活中的应用具有及其重要的意义。在本论文中,我们选取两种非常重要的宽禁带半导体材料:ZnO和GaN,作为研究对象。采用化学工程、能带理论等方法作为研究、制备和设计ZnO和GaN材料的手段。针对目前人们对ZnO和GaN材料制备过程、实际应用中遇到的一些关键问题,对制备过程——微观结构——物理性质之间的关系进行研究,从而实现对材料的微结构和性能的调控,并结合理论计算的研究对实验过程与结果进行解释和验证,探索材料的性能——结构——过程之间的基本规律,为实现材料的规模化生产提供指导和理论依据。在第一章中,简单介绍了半导体材料的分类、几种重要的物理性质以及影响半导体材料性能的因素。并简单的介绍了宽禁带半导体,特别是ZnO和GaN材料的晶体结构、发展现状、物理性质及应用情况。在第二章中,采用水热法,通过在反应溶液中加入表面活性剂制备了氧化锌纳米棒和FTO导电玻璃衬底上取向排列的ZnO纳米棒阵列。通过XRD、SEM、UV-vis分光光度计、PL等对ZnO纳米棒及纳米棒阵列的形貌、结构、光学性质等进行了表征,并对其发光机理进行了系统的研究。通过在反应溶液中添加PVA和PEG作为表面活性剂,可以有效抑制ZnO沿（100）和（101）方向的生长,降低ZnO生长过程中出现的团聚现象,并且使ZnO的带边发光峰消失,出现新的紫光发射峰。通过PVA表面活性剂的添加,氧化锌纳米棒阵列的取向性相对于未添加任何表面活性剂的样品有了明显的改善。氧化锌纳米棒阵列的透过率也大幅提高。同添加PVA表面活性剂生长的氧化锌纳米棒一样,PVA的加入使得原有的氧化锌带边发射峰消失,而在紫光区域产生新的发射峰。为了研究其发光机理,我们对所生长的氧化锌纳米棒阵列进行了一系列不同气氛下的退火处理。另外,我们还对氧化锌纳米棒阵列的光催化性能进行了研究。在第三章中,采用共沉淀法成功制备了氧化锌/氧化铟纳米异质p-n节光催化材料。通过系统的研究退火温度、反应物的初始浓度以及Zn/In比例对所制备的样品的光催化活性的影响,我们得到了制备该体系的最佳条件:Zn/In=1:1,Zn²⁺的初始浓度为20mM,退火温度为800℃。通过各种表征手段,对氧化锌/氧化铟异质结纳米材料的结构、形貌、界面结构进行了研究。通过研究该体系不同样品的光催化效果,并研究造成不同光催化效果的原因,讨论了其能带结构及载流子在光催化反应中的传输过程,探索了该体系地光催化机理。最重要的是,通过制备氧化锌/氧化铟纳米异质结光催化材料,成功验证了异质结或p-n节对光催化活性的影响,并对今后结合半导体的能带理论,通过设计能带结构制备具有特殊用途的可见光响应的高效光催化材料提供了基础,对光催化材料的发展具有重要的意义。在第四章中,采用碳热法制备了氮化镓以及氧化锌/氮化镓固溶体纳米材料。通过改变反应原料中活性炭的比例,制备了一系列不同的样品,研究了利用碳热法制备的氮化镓、氧化锌/氮化镓固溶体材料的结构、形貌以及生长过程。在碳热法制备纳米材料的过程中初始原料中C的比例对材料的生长过程以及形貌会产生重要的影响。通过一系列的测试表征对碳热法制备氮化镓、氧化锌/氮化镓材料的生长机理进行了探究。通过试验结果分析,我们发现碳热法是一种对材料的形貌、结构进行调控的简单有效的制备方法。但利用碳热法制备的氮化镓以及氧化锌/氮化镓材料的物理性质以及晶体结构对称性方面的研究仍需要进一步深入的研究。在第五章中,采用碳热还原氨化法制备了Mn/C共掺杂的氮化镓纳米材料。在不同的C/Ga比例情况下制备的Mn/C共掺杂氮化镓材料具有不同的形貌。通过XPS分析了样品中Mn和C元素的含量及成键状态,证明了Mn和C成功掺入了氮化镓晶格。室温磁性的研究表明,Mn/C共掺杂的氮化镓纳米材料比单纯Mn掺杂的氮化镓材料的饱和磁化强度高大约40倍,并且样品的饱和磁化强度随着C/Ga比例的升高而稳步增加。这提供了一种通过调节初始原料中C/Ga比例,对氮化镓的形貌及其铁磁性质进行控制的方法。结合密度泛函理论计算,研究了Mn原子和C原子在氮化镓晶格内的占据位置,并且讨论了Mn/C共掺氮化镓体系的磁性。计算结果表明Mn和C共同掺入氮化镓晶格时,Mn优先占据Ga的位置,C优先占据N的位置,并且当Mn和C共同掺入氮化镓晶格时,能够大大提高Mn原子的掺入量。磁性方面,C的共掺杂能大大提高体系的铁磁性,并有效抑制向反铁磁态的转变。在第六章中,采用碳热法制备了Fe、Ni掺杂的氮化镓纳米材料。研究了其不同组分下制备的样品的结构、形貌以及磁学性质。我们发现通过改变初始原料中C的比例,样品的形貌会相应改变。同时,样品的磁性也会相应的变化。在第七章,对本论文的工作进行了总结,并对现有研究工作存在的问题进行了分析与讨论。同时,针对目前的工作存在的问题,对未来的研究工作进行了规划与展望。总之,半导体材料,特别是宽禁带半导体材料对人类未来的发展和科学水平的提高具有非常重要的意义。在本论文中,我们通过研究ZnO和GaN基系列材料制备过程——微观结构——材料性能之间的关系,实现了对ZnO和GaN基系列材料的微结构与性能的调控,探索了材料制备过程中性能——结构——过程之间的基本规律,这对于改善和提高ZnO和GaN材料的性能以及实现材料的规模化应用具有非常重要的理论指导意义。更多还原

【Abstract】 The development of material science is a symbol of human civilization.During the thousand years of human history,we experienced Anthropolithic Age,Bronze Age and Iron Age.Now we have entered the Information Age based on semiconductor materials and devices.With the rapid development of science and technology, people’s demands on materials are increasing.So it is very important to explore and study new materials with superior properties.Wide band-gap semiconductor is one of them,which used to fabricate high power,high frequency and high temperature devices for future electronic devices.Since the discovery of nanomaterials in the 80s of 20^th century,people began to realize that the properties of materials are not only determined by the chemical compositions,but also have close relationship with the microstructures and aggregating states of materials.While the microstructures and aggregating states are affected by the synthetic procedure,techniques and engineering,etc.So it is important to investigate the influences of the macroscopic state,such as synthetic procedure, morphology,structure,etc,on the intrinsic structures and electron distributions to improve the physical properties of materials.It is also important to the development of materials science and practical applications.In this thesis,we chose zinc oxide and gallium nitride,which are two of the most important wide band-gap semiconductors,as the objective of our studies.We took chemical engineering and band-gap theory as the theoretical foundation on the synthesis and designing of ZnO and GaN materials.By systematically investigation of the relationship on synthetic procedures,microstructures and physical properties of ZnO and GaN to point against the key problems and hot spots on the scientific research and practical applications,we successfully modulated the microstructures and improved the physical properties of these materials.And our results have been further verified by theoretical calculations.We explored the basic rule on the relationship of procedure,structure and properties of ZnO and GaN,and provided an experimental sample and a theoretical foundation for large scale practical applications.In chapter one,we briefly introduced the categories,physical properties and development of semiconductor materials.And we also discussed the factors which can affect the properties of materials.Some basic information about ZnO and GaN are also presented.In chapter two,we synthesized ZnO nanorods and highly oriented ZnO nanorod arrays on FTO substrate by a simple hydrothermal method with PVA or PEG surfactant in the reaction.We performed X-ray diffractions,scanning electron microscopy,UV-vis spectra,photoluminescence,etc.to investigate the structures, morphologies and optical properties of our samples.We found that the addition of PVA or PEG as surfactant during the hydrothermal process can modulate the growth procedure and morphologies of ZnO materials.The growth along（100） and（101） directions can be prohibited and the agglomeration of ZnO nanorods can be reduced. Furthermore,the addition of surfactant can change the photoluminescence properties of ZnO materials,the intrinsic emission in UV region disappeared,and a new emission at visible violet region appeared.For the highly oriented ZnO nanorod arrays,the directions and the optical transmission of the ZnO nanorod arrays can be greatly improved by adding PVA as surfactant during the hydrothermal process.We investigated the growth process and the photoluminescence properties of ZnO nanorod arrays.The photoluminescence mechanism for the arrays was obtained by performing a series of annealing treatment under different atmospheres. Photocatalysis properties of the ZnO nanorod arrays were also studied.In chapter three,we designed and synthesized ZnO/In₂O₃ p-n hetero-nanostructures by co-precipitation method.We systematically investigated the influence of Zn/In in the starting materials,annealing temperatures,concentration of the precursor solutions on the compositions of our samples and the photocatalytic properties.According to our experimental analysis,the optimized condition for ZnO/In₂O₃ hetero-compositions are Zn/In=1:1 with the starting Zn²⁺ concentration of 20 mM,annealing under 800℃.We investigated the structures,morphologies and the interface of the heteronanostructure by various means.And the interface and the energy band structure of the ZnO/In₂O₃ composite were also investigated.The ZnO/In₂O₃ heteronanostructures are proven to be efficient in the separation of the photogenerated hole-electron pairs and have a high photocatalytic activities based on our systematic analysis.And the designing of the semiconductor heteronanostructures is regarded as a potential way in the development of future photocatalysts for particular applications.In chapter four,we synthesized GaN and ZnO@GaN solid solution nanomaterials by carbothermal nitridation method.By changing the initial Ga/C or Zn/C ratios in the starting materials,we synthesized a series of different samples.We investigated the structures,morphologies and growth process of GaN and ZnO@GaN materials.As we found,charcoal in the starting materials plays an important roles in controlling the morphologies of GaN and ZnO@GaN nanomaterials during the carbothermal nitridation procedure.We proposed a plausible growth mechanism of these nanomaterials based on our experimental data.According to our studies,we regarded carbothermal nitridation method a simple but effective way to modulate the morphologies of GaN and ZnO@GaN nanomaterials.Further investigations on the crystalline symmetry of ZnO@GaN solid solution nano-composites are under progress.In chapter five,we synthesized Mn/C codoped GaN nanomaterials by carbothermal nitridation method using charcoal as the carbon source.The bonding states of Mn and C atoms,characterized by XPS,confirm the doping of both Mn and C atoms into the GaN lattice.Nanostructures such as zigzag nanowires,nanoscrews, and hexagonal nanocones can be produced by controlling the reaction time and the C/Ga molar ratio in the starting mixture.Room-temperature magnetization measurements show that the saturation magnetization of Mn/C codoped GaN can be greater than the Mn doped GaN by a factor up to～40 and increases steadily with increasing Ga/C molar ratio in the starting mixture at a rate of～0.023 emu/g per C/Ga molar ratio.Further investigations are necessary to learn how to control the morphology and the ferromagnetism of Mn doped GaN more precisely.Our DFT calculations support the experimentally deduce suggestion that carbon doping in GaN favors the N sites over the Ga sites,Mn/C codoping strongly enhances the preference of FM coupling over the AFM coupling between the two doped Mn sites.Further investigations are necessary to learn how to control the morphology and the ferromagnetism of Mn doped GaN more precisely.In chapter six,we synthesized Fe,Ni doped GaN nanomaterials by the same carbothermal nitridation method.We characterized the structures,morphologies and ferromagnetic properties by various means.We found the saturation magnetization and the coercive force of Fe doped GaN and Ni doped GaN varied a lot with the change of Ga/C ratios in the starting materials.Further investigations are needed to learn the origins and relationship of the magnetic properties and the Ga/C ratios.In chapter seven,we summarized our work and discussed the problems remained to be solved.At last,we made a plan for the future work and looked forward to the futurity.Material science is one of the most important parts of natural science,and has profound influence on both the development of human civilization and the exploration of science.In this thesis,we investigated the relationship of synthetic procedures, microstructures,and physical properties of ZnO and GaN based nanomaterials,and modulated the microstructures to improve their properties.Our studies on the microstructure modulation and properties characterization of ZnO and GaN based nanomaterials are proven to be an important and efficient way to improve the properties these nanomaterials.And it is also important for the practical applications of ZnO and GaN based nanomaterials in the future.更多还原