Ultra energy efficient III-nitride/polymer hybrid white LEDs using nanotechnology

在过去的十年中，iii -氮化物光源的发展取得了巨大的进步，它的出现显著地改变了我们生活的许多方面。来自iii -氮化物家族的材料可以发出整个可见光谱和紫外线（UV）的主要部分的光，非常适合于白光光源。固态照明的发展正在稳步进行，并将导致近乎终极的照明光源，可能基于iii -氮化物材料。这将导致照明概念的根本改变，并有可能导致大量的能源节约，估计到2020年相当于1120亿美元。由于日益严重的全球能源危机和全球变暖的威胁，这种效率的提高变得越来越重要。目前，制造固态照明所需的白光发光二极管（LED）有三种主要方法：(1)由三个LED芯片组成的封装，每个芯片以不同的波长（分别为红、绿、蓝）发光；(2)蓝色（460纳米）LED与黄色荧光粉的组合，该荧光粉由LED发出的蓝光泵浦；(3)单一晶片发出紫外光，该紫外光被三种荧光粉（红、绿、蓝）吸收，并以广谱白光的形式重新发射。第一种方法对于实现真正的白光光源是理想的，但是要平衡这些不同颜色的电致发光强度是非常困难的，并且存在许多与单个led的不同要求相关的基本挑战。目前uv - led的性能远低于蓝色led，这是第三条路线的主要限制。因此，蓝色LED+荧光粉方法在制造白光LED方面保持了强大的领先优势，并取得了几项商业成功。然而，最有前途的商用白光led是基于具有最高晶体质量的蓝色晶圆片，因此非常昂贵。这提高了价格，从而限制了它们在一般照明中的应用。该技术的进一步发展也仍然面临着问题，这也是本文提出新型LED的动力所在。我们的目标是开发一种混合纳米技术，提供一种新型的超高能效白光led，而不需要昂贵的蓝色外延晶圆。混合的技术是半导体纳米棒阵列，尺寸在100纳米尺度上，金属纳米粒子和聚合物。在我们展示共轭聚合物高效发光的基础上，我们将优化这些材料，将蓝光转化为黄色。新的聚合物将用于填充gan基LED结构中制备的纳米棒之间的空间，最大限度地增加蓝色光源和黄色发射器之间的接触。由于金属和半导体之间的耦合效应，将银纳米颗粒混合到聚合物中将用于进一步改善光学性能。相对较厚的封盖层通常会限制这种效果的强度，但聚合物/金属混合物与纳米棒侧壁之间的紧密接触使我们能够接近这种效果的全部好处。这项工作将结合谢菲尔德大学在iii -氮化物器件制造和iii -氮化物发射器表征方面的现有优势，以及斯特拉斯克莱德大学在聚合物化学、iii -氮化物基础光学研究和纳米结构表征方面的优势，包括金属纳米颗粒和半导体。这项联合努力的目的是提高对上述光学发射过程中基本问题的理解，并优化混合iii -氮化物/聚合物白光led的制造工艺。这将导致下一代白光led在成本和发光效率方面适合取代传统光源的示范。

The last decade has seen dramatic advances in the development of III-nitride light emitters, whose emergence is significantly changing many aspects of our lives. Materials from the III-nitride family can emit light over the complete visible spectrum and a major part of the ultraviolet (UV) and are ideally suited for white light sources. Developments in solid-state lighting are occurring at pace and will lead to near-ultimate lighting sources, likely to be based on III-nitride materials. This will result in a fundamental change in the concept of illumination and has the potential to lead to massive savings in energy, estimated to be equivalent to $112 billion by the year 2020. Such increases in efficiency are increasingly important due to the growing world-wide energy-crisis and threat of global warming.Currently, there are three main approaches for the fabrication of white light emitting diodes (LEDs) needed for solid-state lighting: (1) a package of three LED chips each emitting at a different wavelength (red, green and blue, respectively); (2) a combination of a blue (460 nm) LED with a yellow phosphor pumped by blue light from the LED; (3) a single chip emitting UV light which is absorbed by three phosphors (red, green and blue) and reemitted as a broad spectrum of white light. The first method is ideal for achieving a true white light source, but it is extremely difficult to balance the electro-luminescence intensities of these different colours and there exist a number of fundamental challenges related to the different requirements of the individual LEDs. The performance of current UV-LEDs is far below blue-LEDs and presents a major limitation to the third route. As a result the blue LED+ phosphor approach is maintaining its strong lead for the fabrication of white LEDs with several commercial successes. However, the most promising commercially available white LEDs are based on blue epiwafers with the highest crystal quality, which are thus extremely expensive. This raises the price and thus limits their applications in general illumination. Further development of the technology is also still faced with problems, which are the driving force behind the new type of LED proposed here. We aim to develop a hybrid nanotechnology delivering a new type of ultra high energy efficient white-LED without need for the premium price blue epiwafers. The technologies to be hybridised are arrays of semiconductor nano-rods, with dimensions on the scale of 100s of nanometres, metal nano-particles and polymers. Building on our work demonstrating efficient light emission from conjugated polymers we will optimise these materials for converting blue light to yellow. The new polymers will be used to fill the spaces between nanorods prepared in GaN-based LED structures, maximising the contact between the blue light source and the yellow emitter. Blending silver nano-particles into the polymer will be used to further improve optical performance as a result of a coupling effect between the metal and semiconductor. Relatively thick capping layers usually limit the strength of this effect but the close contact between the polymer/metal blend and the side-walls of the nano-rods enables us to get close to the full benefit.This work will combine the existing strengths at the Sheffield in III-nitride device fabrication and characterisation of III-nitride emitters with those at Strathclyde in polymer chemistry, fundamental optical studies of III-nitrides and characterization of nanostructures, including metal nanoparticles and semiconductors. This combined effort aims to achieve an improved understanding of the fundamental issues in the optical emission processes mentioned above and to optimise fabrication processes of hybrid III-nitride/polymer white LEDs. It will lead to the demonstration of next generation white-LEDs suitable for replacement of conventional light sources in terms of cost and luminous efficacy.