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Materials Challenges in GaN-based Light Emitting Structures

GaN 基发光结构的材料挑战

基本信息

批准号：
EP/E035167/1
负责人：
Colin Humphreys
金额：
$ 173.56万
依托单位：
University of Cambridge
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2006
资助国家：
英国
起止时间：
2006 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FE035167%2F1
关键词：
Materials Challenges GaN based Light

项目摘要

Gallium nitride (GaN) is an amazing material that can emit brilliant light. GaN light emitting diodes (LEDs) first became available about ten years ago, and are already used in a wide range of applications, including interior lighting in cars, buses and planes; traffic lights, large full-colour displays and backlighting in mobile phones. GaN blue lasers are about to be sold for next-generation DVD players, in which the DVDs will contain up to ten times the amount of music or pictures as existing DVDs. Looking to the future, GaN may make possible high-quality, high efficiency white lighting which will produce major energy savings. Another exciting development could be high-efficiency deep ultra-violet LEDs for water purification, particularly in the developing world.Unfortunately, we are currently unable to make the high-efficiency white lighting and deep-UV LEDs referred to above because there are some key scientific problems that remain to be solved. To successfully surmount these challenges requires a detailed understanding of the complex processes involved in the fabrication of the light emitting regions of the LED. These consist of thin layers of an alloy called InGaN, which are sandwiched between thicker layers of GaN to make structures called quantum wells. These quantum wells are 50,000 times thinner than a human hair. We must also understand the processes that limit light emission and optimise the electrical conductivity of the many other semiconductor layers in an LED. Following on our highly successful work on GaN of the last five years which has put us into an internationally competitive position, we have put together a team of leading researchers from different universities and industry to attack the critical factors that limit the performance of GaN-based LEDs.One key limitation to our understanding is the reason why GaN blue LEDs emit brilliant light even though they are full of defects called dislocations that should quench the light emission arising from the quantum wells. This is hotly debated and in 2005 two major international conferences had special sessions devoted to discussing this topic. Our theory is that the light-emitting InGaN quantum wells have atomic scale thickness fluctuations on a nanometre lateral scale, and thus the light emission is mainly localised in tiny nanometre-scale regions away from the dislocations. However, this localisation is much weaker for UV LEDs, and so unfortunately dislocations strongly quench the light emission in these devices.A major thrust of our research is to understand how the electrical carriers whose interaction is responsible for the light emission are localised, and kept away from defects which would otherwise quench the light emission, and then to optimise this localisation. This may be achieved by engineering the growth of the quantum wells. To understand the quantum wells we will not only examine the light they emit, but use microscopes that allow us to visualise objects far smaller than the wavelength of light to image detailed, atomic-scale variations within the light emitting regions. Quantum structures made from GaN also have strong internal electric fields which can reduce the light emission. We will use specialist microscopy techniques to measure these fields, and study ways of reducing them.Another focus is to develop new methods of reducing the density of defects in crystals called dislocations. Additionally, we will study the electrical properties of the GaN material which surrounds the quantum wells in an LED, in order to understand what defects prevent electrical conduction and reduce their occurrence. Our research involves crystal growers, electron microscopists, experts in optical and electrical characterisation techniques, theoretical and experimental physicists, chemists, and materials scientists. Only this type of integrated approach can solve the challenging problems in GaN-based technology.

氮化镓（GaN）是一种令人惊叹的材料，可以发出明亮的光。GaN发光二极管（LED）在大约10年前首次上市，并且已经被广泛应用，包括汽车、公共汽车和飞机的内部照明;交通信号灯、大型全彩显示器和移动的手机的背光。GaN蓝色激光器将用于下一代DVD播放器，其中DVD包含的音乐或图片数量将是现有DVD的十倍。展望未来，GaN可能使高质量、高效率的白色照明成为可能，这将节省大量能源。另一个令人兴奋的发展可能是用于水净化的高效深紫外LED，特别是在发展中国家。不幸的是，我们目前无法制造上面提到的高效白色照明和深紫外LED，因为还有一些关键的科学问题有待解决。为了成功克服这些挑战，需要详细了解LED发光区域制造中涉及的复杂工艺。这些由一种叫做InGaN的合金薄层组成，它夹在较厚的GaN层之间，形成称为量子威尔斯的结构。这些量子威尔斯比人的头发细5万倍。我们还必须了解限制发光和优化LED中许多其他半导体层导电性的过程。在过去五年中，我们在GaN方面的工作非常成功，使我们处于国际竞争地位，我们已经召集了一个由来自不同大学和行业的领先研究人员组成的团队，以解决限制GaN性能的关键因素，我们理解的一个关键限制是为什么GaN蓝色LED发出明亮的光，即使它们充满了称为位错的缺陷。这将抑制从量子威尔斯产生的光发射。这是一个激烈的辩论，2005年，两个主要的国际会议举行了专门讨论这一主题的特别会议。我们的理论是，发光InGaN量子威尔斯在纳米横向尺度上具有原子尺度的厚度波动，因此发光主要局限于远离位错的微小纳米尺度区域。然而，这种局部化对于UV LED来说要弱得多，因此不幸的是，位错强烈地淬灭了这些器件中的光发射。我们研究的一个主要目标是了解相互作用负责光发射的电载流子是如何局部化的，并且远离否则会淬灭光发射的缺陷，然后优化这种局部化。这可以通过设计量子威尔斯的生长来实现。为了理解量子威尔斯，我们不仅要检查它们发出的光，还要使用显微镜，使我们能够可视化远小于光波长的物体，以成像发光区域内详细的原子级变化。由GaN制成的量子结构也具有强的内部电场，这可以减少光发射。我们将使用专业的显微镜技术来测量这些场，并研究减少它们的方法。另一个重点是开发减少晶体中称为位错的缺陷密度的新方法。此外，我们还将研究LED中量子威尔斯周围GaN材料的电学特性，以了解哪些缺陷会阻止导电并减少其发生。我们的研究涉及晶体生长者，电子显微镜，光学和电学表征技术专家，理论和实验物理学家，化学家和材料科学家。只有这种类型的集成方法才能解决GaN基技术中的挑战性问题。