Next generation white LEDs using hybrid inorganic/organic semiconductor nanostructures for general illumination and wireless communication

由于世界能源危机和气候变化，对可持续节能技术的需求显著增加。由于一般照明所消耗的能量约占世界总能量消耗的29%，目前使用的技术效率相当低，通常含有有毒元素。因此，有必要开发超节能的固态照明光源来取代这些白炽灯和荧光灯，对于这些光源，主要候选者主要基于白色发光二极管（LED）。这种白色LED可以由无机或有机半导体制造，其中前者在高亮度和高效率方面处于领先地位。这些由III族氮化物半导体构成，其在整个组成范围内具有直接带隙，覆盖整个可见光谱和紫外线的主要部分。白色LED的快速调制，以肉眼无法察觉的速度，使它们也可以用作无线数据通信的光发射器。这开启了白色LED作为同时照明和无线通信的照明源的令人兴奋的可能性。这是可见光通信（VLC）的新兴技术，并且相对于当今的射频（RF）通信技术具有许多主要优点，例如增加安全性、消除任何RF引起的健康问题等。然而，当前白色LED的性能和成本不足以令人印象深刻以允许目前替换常规照明源。此外，就VLC应用而言，带宽目前被限制在MHz级别，这远低于当前宽带WiFi系统的实际要求。这是由于目前基于III族氮化物的LED的长载流子复合寿命，其常规地以包含强压电场的“极性”取向生长。这些场导致LED的有源区中的电子和空穴波函数之间的重叠减少，其然后遭受长的辐射复合寿命（10-100 ns）以及低的内部量子效率。此外，用于将发射转换为白色光的常规磷光体具有甚至更长的衰减时间，并且对可用带宽呈现额外的限制。该项目将采用非极性III族氮化物，并使用新型纳米纤维技术集成两大半导体家族（有机和无机半导体），以实现具有超快调制速度的超节能LED，用于下一代基于III族氮化物的白色照明。纳米级的结构化将用于III族氮化物层的生长，以获得高质量的非极性GaN，从而消除压电场，从而提供更快，更高效的器件。纳米结构还将用于引入额外的纳米腔效应，进一步降低辐射复合寿命并提高光学效率。该项目的目标是一种新型的混合纳米结构，以实现原型白光LED的调制速度在10 GHz的水平和一个阶跃变化的能源效率与目前的最先进的设备相比，将使用金属有机气相外延和洁净室加工制造，并充分利用光学和电学测量的特点。过程中的每个阶段都将得到优化，与行业的密切合作将确保所产生的方法是实用的，并可扩展到大批量。

There is a significantly increasing demand for sustainable energy-efficient technologies due to the world energy crisis and climate change. The energy consumed due to general illumination accounts for about 29% of the world's total energy consumption, currently using rather inefficient technologies often containing toxic elements. It is therefore necessary to develop ultra energy-efficient solid-state lighting sources to replace these incandescent and fluorescent lights, for which the leading candidates are mainly based on white light emitting diodes (LEDs). Such white LEDs can be fabricated from inorganic or organic semiconductors, with the former leading the way for high brightness and efficiency. These are constructed from III-nitride semiconductors, which have direct bandgaps across their entire composition range, covering the complete visible spectrum and a major part of the ultraviolet. Fast modulation of the white LEDs, at speeds undetectable to the eye, allows them to also be utilised as optical transmitters for wireless data communication. This opens up the exciting possibility of white LEDs serving as lighting sources for simultaneous illumination and wireless communication. This is the emerging technology of visible light communication (VLC) and has a number of major advantages over the present-day radio frequency (RF) communication technology, such as increasing security, eliminating any RF-induced health concern, etcHowever, the performance and cost of current white LEDs is not sufficiently impressive to allow replacement of conventional lighting sources at the moment. Furthermore, in terms of VLC applications, the bandwidth is currently limited to the MHz level, which is well below the practical requirements of current broadband WiFi systems. This is due to the long carrier recombination lifetime of current III-nitride based LEDs, which are conventionally grown in a "polar" orientation containing intense piezoelectric fields. These fields result in a reduced overlap between the electron and hole wavefunctions in the active regions of the LEDs, which then suffer from long radiative recombination lifetimes (10-100 ns) and also low internal quantum efficiency. In addition, the conventional phosphors used to convert the emission to white light have even longer decay times and presents an additional limitation on the available bandwidth. The project will employ non-polar III-nitrides and integrate the two major semiconductor families (organic and inorganic semiconductors) using a novel nanofabrication technology in order to achieve ultra energy efficient LEDs with ultrafast modulation speeds for next generation III-nitride based white lighting. Structuring on a nanometre scale will be used in the growth of the III-nitride layers to achieve high quality non-polar GaN, thereby eliminating the piezoelectric fields to give faster, more efficient devices. The nanostructures will also be used to introduce extra nanocavity effects, further reducing the radiative recombination lifetime and increasing the optical efficiency. The target of the project is a novel hybrid nanostructure to achieve prototype white-LEDs with a modulation speed on a level of 10 GHz and a step change in energy efficiency compared with the current state-of-the-art. The devices will be fabricated using metal-organic vapour phase epitaxy and cleanroom processing and fully characterised using optical and electrical measurements. Each stage in the process will be optimised and close working with industry will ensure that the resulting methods are practical and scalable to high volumes.