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Fundamental studies of zincblende nitride structures for optoelectronic applications

用于光电应用的闪锌矿氮化物结构的基础研究

基本信息

批准号：
EP/R010250/1
负责人：
David Binks
金额：
$ 63.12万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2018
资助国家：
英国
起止时间：
2018 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FR010250%2F1
关键词：
Fundamental studies zincblende nitride structures

项目摘要

Over the last fifteen years there has been a revolution in terms of the availability and efficiency of GaN based light emitting diodes (LEDs) that emit principally blue light but also green light. These LEDs have found widespread application in displays, local monochrome lighting and most importantly so-called Solid State Lighting (SSL), in other words LED light bulbs. In an LED bulb, the white light is produced by mixing the blue light from an LED with yellow light from a phosphor. Some of the LED light is transformed into yellow light by the phosphor in a process called "down-conversion". The biggest advantage of LED bulbs is that they are much more efficient than incandescent or compact fluorescent light bulbs. Lighting uses about 20% of global electricity production, and has been identified as the single most wasteful component of domestic electricity use. SSL based on GaN LEDs, has the potential to reduce the consumption of energy used by lighting by a factor of 4. Down-converting blue light intrinsically wastes energy, and if the phosphor could be replaced by LEDs emitting other colours (green and red) with similar performance as the blue LED, the efficiency of SSL could be improved by 15 - 20%. At the moment, according to the US Department of Energy (Bardsley N et al. 2015 "US Department of Energy 2015 Solid-State Lighting R&D Plan"), the Power Conversion Efficiencies (PCE) of blue and green LEDS when operated to give sufficient light to illuminate a room are 60% and 22% respectively. The target PCE figures for the year 2020 from this report are blue 80% and green 35%. To achieve the stated improvements in PCE means that the IQE of blue and green emitters has to be increased significantly. Yet despite decades of research and development the best IQE values for both blue and green emitters have plateaued with little promise of any further significant improvements being achieved using the conventional technology.In this program we propose to develop a new form of technology that could lead to LEDs with significant increases in IQE. At the moment the GaN based crystals that make up the active light emitting regions of LEDs are such that the atoms are arranged in a hexagonal pattern. This has the consequence that when an electron is injected into the crystal to generate light, the light emission process is slow, leaving plenty of time for the electron to lose energy by other processes that do not lead to light emission. These "non radiative" processes limit the IQE of LEDs. In this work we propose to produce cubic GaN crystals in such a form that the time for electrons to generate light is greatly reduced, thus offering up the possibility of LEDs with increased efficiency.There are several challenges to be overcome in achieving this goal. Firstly the fabrication of cubic GaN without too many mistakes in the crystal's structure is very difficult. The main problem to be overcome is a natural tendency for the crystals to have faults in the way layers of atoms stack. We intend to study in depth the crystal growth process enabling us to eliminate this problem and produce crystals with many fewer faults. Secondly we must be able to control the ability of the GaN to conduct electricity so that we can successfully fabricate LEDS. We will investigate the processes whereby the conductivity may be limited with the aim of producing high conductivity material. Thirdly we will determine the details of the light emission process to determine whether the promise of higher efficiency is fulfilled.

在过去的十五年中，在主要发射蓝光但也发射绿色光的GaN基发光二极管（LED）的可用性和效率方面已经发生了革命。这些LED已经广泛应用于显示器、局部单色照明以及最重要的所谓固态照明（SSL），换句话说，LED灯泡。在LED灯泡中，通过将来自LED的蓝光与来自磷光体的黄光混合来产生白色光。一些LED光在称为“下转换”的过程中被荧光粉转化为黄光。LED灯泡的最大优点是它们比白炽灯或紧凑型荧光灯泡效率高得多。照明使用约20%的全球电力生产，并已被确定为家庭用电中最浪费的组成部分。基于GaN LED的SSL有可能将照明所使用的能源消耗减少4倍。下转换蓝光本质上浪费能量，并且如果磷光体可以被发射具有与蓝光LED类似性能的其他颜色（绿色和红色）的LED替代，则SSL的效率可以提高15 - 20%。目前，根据美国能源部（Bardsley N et al.2015“US Department of Energy 2015 Solid-State Lighting R&D Plan”），蓝色和绿色LED的功率转换效率（PCE）在被操作以给出足够的光来照亮房间时分别为60%和22%。本报告中2020年的目标PCE数字为蓝色80%和绿色35%。为了实现PCE的所述改进，意味着必须显著增加蓝色和绿色发射体的IQE。然而，尽管经过几十年的研究和开发，蓝色和绿色发光体的最佳IQE值已经趋于稳定，几乎没有任何进一步的显着改进的希望，使用传统的技术。在这个项目中，我们建议开发一种新的技术形式，可以导致LED的IQE显着增加。目前，构成LED的有源发光区的GaN基晶体是这样的，即原子以六边形图案排列。这导致当电子被注入晶体中以产生光时，光发射过程是缓慢的，留下足够的时间让电子通过不导致光发射的其他过程损失能量。这些“非辐射”过程限制了LED的IQE。在这项工作中，我们提出以这样的形式生产立方GaN晶体，即电子产生光的时间大大减少，从而提供了提高LED效率的可能性。在实现这一目标的过程中，有几个挑战需要克服。首先，在晶体结构中没有太多错误的立方GaN的制造是非常困难的。要克服的主要问题是晶体在原子层堆叠方式上存在缺陷的自然趋势。我们打算深入研究晶体生长过程，使我们能够消除这个问题，并生产出缺陷更少的晶体。其次，我们必须能够控制GaN的导电能力，以便我们能够成功地制造LED。我们将调查的过程中，导电性可能是有限的，目的是生产高导电性材料。第三，我们将确定发光过程的细节，以确定是否实现了更高效率的承诺。