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About this book

The book provides an overview of III-nitride-material-based light-emitting diode (LED) technology, from the basic material physics to the latest advances in the field, such as homoepitaxy and heteroepitaxy of the materials on different substrates. It also includes the latest advances in the field, such as approaches to improve quantum efficiency and reliability as well as novel structured LEDs. It explores the concept of material growth, chip structure, packaging, reliability and application of LEDs. With spectra coverage from ultraviolet (UV) to entire visible light wavelength, the III-nitride-material-based LEDs have a broad application potential, and are not just limited to illumination. These novel applications, such as health & medical, visible light communications, fishery and horticulture, are also discussed in the book.

Table of Contents

Frontmatter

Chapter 1. Introduction

Abstract
Since ancient times, history of artificial lighting sources has been closely related to the development of human civilization. Lighting source is not only the witness of human civilization, but also the driving force for the continuous development and progress of human civilization.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 2. Basic Principles of LED

Abstract
LED is a semiconductor optoelectronic device. In contrast with traditional light sources, LED has a list of advantages, such as high efficiency, long lifetime, not easy to break, fast reaction speed and high reliability.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 3. Properties and Testing of Group III-Nitride LED Materials

Abstract
The group III nitride semiconductor material mainly includes the compounds GaN, AlN, InN, and their alloys such as AlGaN, GaInN, AlInN, and AlGaInN. The band gap (0.7~6.03 eV) of these materials with the different components covers the whole visible spectrum, which makes the nitride semiconductor materials attractive for a range of applications. However, due to the nature of the nitride material, there are many difficulties in the development process that need further research. The basic properties of nitride semiconductor materials, including crystal structure, band structure, polarization effect, doping, crystal defects and certain characterization methods are studied to measure the physical properties of the materials.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 4. Epitaxial of III-Nitride LED Materials

Abstract
III-nitrides include GaN, InN, AlN and their ternary and quaternary solid solutions. Since they are all direct band gap semiconductors, they are particularly suitable for fabricating light-emitting devices. However, the bulk single crystal growth conditions of the nitride material are complicated and require high temperature and high pressure. The current nitride material is mainly prepared by heteroepitaxial on other substrates.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 5. InGaN/GaN Multiple Quantum Wells Materials as Well as Blue and Green LEDs

Abstract
InGaN/GaN quantum wells are commonly used in III-nitride based blue or green LED chips. Back in the earlier days, it was difficult for GaN materials to be doped for the formation of high crystal quality p-type GaN. In 1986, Hiroshi Amano and Akasaki et al. [1] demonstrated GaN films with a good surface structure and high crystal quality by MOCVD through low-temperature AlN buffer epitaxial layer. In 1989, Amano et al. [2] used low-energy electron irradiation (LEEBI) technology and successfully achieved p-type doping of GaN materials. These breakthrough technologies accelerated the development of LED. This led to the rapid progress in terms of output power, quantum efficiency, spectral quality, etc. However, InGaN/GaN multiple quantum wells LEDs also face many problems such as the polarization effects, quantum confined Stark effect (QCSE), and carrier localization effect. Both the localization effect and the QCSE affect the spontaneous emission of InGaN/GaN multiple quantum wells. Polarization effect and QCSE in InGaN/GaN multiple quantum wells materials become even more obvious with the increase of In incorporation. The development of semi-polar and non-polar LEDs can effectively alleviate these effects on nitride LEDs performance.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 6. AlGaN-Based Multiple-Quantum-Well Materials and UV LEDs

Abstract
Ultraviolet (UV) light, which is shorter than the wavelength of visible light, has important applications in the field of sterilization and disinfection. Among them, UV-C light (250–280 nm) can destroy nucleic acids, the genetic material of microorganisms, through photochemical action.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 7. III-Nitride LED Quantum Efficiency Improvement Technology

Abstract
LED quantum efficiency is one of the important indicators to characterize the performance of LED devices, including internal quantum efficiency and external quantum efficiency. The internal quantum efficiency refers to the radiation recombination efficiency of electron-hole pairs injected into the active region, which can be improved by optimizing the epitaxial structure and improving the epitaxial technology. The external quantum efficiency is the ratio of the number of photons incident into the space and number of electron-hole pairs in the active region, which is the product of the internal quantum efficiency and the light extraction efficiency. The improvement of light extraction efficiency mainly depends on the optimization of chip technology and packaging technology. In addition, the current injection efficiency is also an important factor affecting the wall-plug efficiency of the LED, and is related to the bulk resistance of the LED device, leakage of carriers and electrode contact.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 8. III-Nitride LED Chip Fabrication Techniques

Abstract
With the development of epitaxial growth technology and multi-quantum well structure, the internal quantum efficiency of ultra-high brightness LED has been greatly improved. For example, the internal quantum efficiency of the 625 nm AlGaInP-based LED can reach almost 100%. However, defects caused by the lattice and thermal mismatch, stress and electric field which present in GaN-based materials make the internal quantum efficiency of Group III nitride (AlGaInN-based) LEDs relatively low. For instance, a quantum efficiency typically in the range between 35 and 50% is achieved. Therefore, increasing the external quantum efficiency of the LED chips is the key to improve the luminous efficiency. This largely requires the proper designs of a new chip structure to improve the light-emitting efficiency, thereby achieving much enhanced luminous efficiency (or external quantum efficiency). In the development of III-nitride LED technology for semiconductor illumination, many technical and theoretical issues including material epitaxy, p-doping and activation, material etching, ohmic contact, photoelectric characteristics, current spreading, light-emitting structure, and device protection are being solved or continuously advanced. Mature theories and processes such as p-type GaN annealing activation, ICP etching methods, heavily doped top layer preparation for ohmic contacts, electrode structures, etc. have become the standard in current laboratories and factories, driving the science and technology of semiconductor lighting technology.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 9. Packaging of Group-III Nitride LED

Abstract
Group-III nitride LED encapsulation is one of the key technologies of solid-state lighting. The technology aims to improve light extraction efficiency, beam profile, color conversion, reliability and thermal management of the LEDs. This chapter will mainly introduce the LED related packaging materials, design, process and related technology. In the end, a brief description of the latest LED packaging trends is discussed.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 10. Reliability Analysis of Group III Nitride LEDs Devices

Abstract
In addition to productivity and energy saving, another outstanding advantage of III-nitride LEDs is its long lifetime predicted to reach a record of over 10,000 h. Under normal circumstances, the LEDs would not be instantly total failure, but decays after a period of operation due to the improper design or production process which may not meet the operating requirements.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 11. Applications of LEDs

Abstract
Solid-state lighting (SSL) market is huge, being worth hundreds of billions of dollars. In 2014, output value of SSL product in China was worth more than 350 billion RMB (China Solid State Lighting Alliance Annual Report 2014, [1]). SSL products consist of LED backlight, outdoor lighting, indoor lighting, LED display, etc. This chapter focuses on key areas related to LED applications, including an overview of technologies such as lighting, backlighting, display, communications, and biological applications.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue

Chapter 12. Novel Nitride LED Technology

Abstract
At present, the light efficiency of the high-power white LED has reached 250 lm/W in the industry. The light efficiency reported in the laboratory has exceeded 300 lm/W. The innovation of LED technology and application of LEDs have far exceeded expectations. However, the luminous efficiency of the traditional planar LED with InGaN/GaN multiple quantum well structure is difficult to rise significantly due to some inherent problems. At the same time, the light efficiency is still far away from the theoretical limit of 400 lm/W. In addition, with the demand of some special applications, some new LED technologies such as nanorod LEDs, quantum dot LEDs, polarized LEDs, etc., have been explored. The exploration of the growth, preparation and application of these new LED structures not only contribute to the research of basic physics but also to solve the bottleneck problem in the development of semiconductor lighting by improving the material and device performance and by approaching the theoretical limit of LED lighting. Thus, it has important research value.
Jinmin Li, Junxi Wang, Xiaoyan Yi, Zhiqiang Liu, Tongbo Wei, Jianchang Yan, Bin Xue
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