【作者】 王虎；

【导师】 陈长清；

【作者基本信息】 华中科技大学 ， 光电信息工程， 2013， 博士

【摘要】 紫外波段的AlGaN发光器件对于白光照明、空气和水的净化、消毒杀菌、高密度存储等领域意义重大，因此对AlGaN发光器件的研究成为当下人们关注的焦点。目前生长AlGaN材料普遍使用的衬底是蓝宝石，材料中的穿透位错通常在1010-1012cm-2量级，这严重影响着AlGaN基发光器件的量子效率。经过多年的探索，现在普遍认为的一个解决方案是在蓝宝石衬底上制备高质量的AlN薄膜作为AlGaN器件的模板，在此模板上可以获得高质量无裂纹的AlGaN材料。因此，如何在蓝宝石衬底上制备高质量的AlN模板已经成为AlGaN器件发展的关键一步。目前，由于量子点的独特性能，研究者发现通过在有源区中引入量子点的途径也可以提高器件的量子效率。量子点的尺寸接近于电子的波尔半径，电子的运动被限制在量子点内部，因此载流子的复合概率变大。量子点所表现出的各种量子特性和光学非线性，无论是在基本物理方面还是在器件应用方面（包括激光器、单光子光源和量子计算等）都有巨大的研究价值。本论文的第一部分工作详细介绍了金属有机物化学气相沉积（MOCVD）生长AlN模板的研究。首先采用低温成核层技术和脉冲原子层外延（PALE）技术相结合的方法生长AlN材料，讨论了影响AlN晶体质量和表面形貌的各种因素，研究了生长条件对于生长模式影响的根本原因，从而解决AlN生长中所面临的难题。文中主要研究了衬底表面处理工艺、低温成核层工艺（包括生长温度、厚度以及V/III）和PALE生长工艺（包括生长温度、V/III和生长速率）对于AlN材料的影响。我们发现衬底在不同的处理工艺下，AlN和衬底之间的失配应力的释放机制有所不同。通过氮化处理，可以有效提高晶体的取向性并获得Al极性的AlN材料。通过低温成核层工艺的研究，我们获得了（002）面摇摆曲线半高宽（FWHM）为63arcsec，（102）面半高宽为1106arcsec的样品，其表面完全愈合，没有发现坑（pits）的存在。在成核层的基础上，通过PALE AlN层的生长研究，我们获得了表面无裂纹，厚度达636nm的AlN外延层。在本论文的第二部分工作，主要介绍了量子点生长的研究工作。首先，在AlN模板上研究了GaN量子点的生长工艺。试验中分别采用了S-K（Stranski-Krastanov）生长模式和Ga droplets epitaxy的方法制备GaN量子点。在S-K生长模式中，研究了生长时间、反应物流量、生长压强和生长温度对GaN量子点形貌的影响。虽然由于生长速率太高无法获得GaN量子点，但实验结果表明如果生长厚度能够精确控制的话，通过生长工艺的优化可以在S-K模式下获得GaN量子点。在Ga droplets epitaxy方法制备GaN量子点过程中，则讨论了各步生长工艺对于量子点的影响，初步实现了控制GaN量子点尺寸、密度和质量的生长条件。量子点横向尺寸在100nm以内，纵向尺寸在10nm以内，密度在108cm-2到1010cm-2量级间可控，并在310nm处观测到光致发光（PL）峰。然后在Ga droplets epitaxy方法形成的GaN量子点的基础上，研究了量子点caplayer的生长工艺，在合适的生长条件下获得了表面平整的AlNcaplayer。最后，在P-GaN模板上通过Ga droplets epitaxy的方法实现了GaN量子点的制备，并研究其生长工艺对于量子点形貌的影响。然后，我们在GaN模板上通过S-K方法制备了InGaN量子点，试验中通过生长温度、生长速率和In组分等因素控制InGaN量子点的尺寸和密度，获得了横向尺寸在20-80nm，纵向尺寸在2-15nm，密度在1010cm-2量级的InGaN量子点。更多还原

【Abstract】 AlGaN based emitting devices have been attracting considerable attention because ofits significant application in the ultraviolet field such as white light illumination, air andwater purification, sterilization, high-density storage. The common substrate for growingAlGaN materials is sapphire. The quantum efficiency of AlGaN based emitting devices issignificantly affected by the high density of dislocation like1010-1012cm-2in materialsgrowing on sapphire substrates. After years of exploration, one of the recognized solutionsis growing high quality AlN templates for AlGaN devices on sapphire substrates. ThickAlGaN films without crack can be obtained on these AlN templates. Growing high qualityAlN templates on sapphire substrates has been a key step for AlGaN devices. In nowadays,researchers are inserting quantum dots into the active layer of AlGaN devices to increasethe quantum efficiency due to its specific performance. The scale of quantum dots isrelated to Bohr radius of the electron, the movement of electrons is confined in quantumdots, and the recombination prlbility of carrier increases. The investigation of growingquantum dots is valuable in both basic physics research and device applications (includelasers, single optical sources, quantum calculation).The first part of this dissertation describes the investigation of AlN templates viametalorganic chemical vapor deposition (MOCVD) in detail. A combined growthtechnical, a low temperature nucleation layer and pulsed atom layer epitaxy (PALE), hasbeen applied for growing AlN materials firstly. The effects of growth conditions on thequality of AlN films and also AlN growth mode are investigated to solve the problems ingrowing AlN films. The effects of pretreatment of sapphire substrates, low temperaturenucleation layer growth conditions (include growth temperature, layer thickness, V/III),and PALE growth conditions (include growth temperature, V/III, and growth rate) on AlNfilms are mainly studied. With different pretreatment conditions, different strain relaxationmechanisms induced by the lattice mismatch of AlN and sapphire are observed. Thenitridation pretreatment eliminates the misoriented crystals and the resulted AlN is Al-face.By optimizing the growth conditions of AlN films, samples with (002) full width of halfmaximum (FWHM) of52arcsec and (102) FWHM of1106arcsec are obtained. Thesamples are coalescence completely without any pits. Based on the nucleation layer, a 636nm thick AlN layer without cracks is obtained through PALE growth technical.The second part of this dissertation describes the investigation of growing quantumdots. The growth of GaN quantum dots on AlN templates is investigated firstly. Thegrowth methods of GaN quantum dots include S-K (Stranski-Krastanov) growth mode andGa droplets epitaxy. The effects of the growth condition such as growth time, flux, reactorpressure, and growth temperature on the morphology of GaN quantum dots areinvestigated in S-K growth mode. GaN quantum dots are not achieved during ourexperiments due to the high growth rate. However, the results show that GaN quantumdots could be realized by S-K growth mode if the growth thickness of GaN quantum dotscould be controlled. During the experiments of Ga droplets epitaxy, the effects of eachgrowth process on the GaN quantum dots are investigated. Based on the experiments, thesize, density, and quality of GaN quantum dots are controlled by the growth conditions.The horizontal and vertical size of quantum dots are less than100nm and10nm with adensity varied between108cm-2and1010cm-2. An emission peak at310nm is observed inPL spectrum. Then, the growth conditions of caplayer are investigated on Ga dropletsepitaxy quantum dots. Samples with flat AlN caplayer are obtained under optimalconditions. GaN quantum dots are also grown on P-GaN templates through Ga dropletsepitaxy. The effects of growth conditions on the morphology of GaN quantum dots areinvestigated.At last, the growth of InGaN quantum dots on GaN templates is investigated via S-Kgrowth mode. The size and density of InGaN quantum dots are controlled by the growthconditions such as growth temperature, growth rate, and In content. InGaN quantum dotswith20-80nm wide,2-15nm high, and density of1010cm-2are obtained.更多还原