Depth comparison of semiconductor lighting three main technical route

In the process of LED, the substrate material is the main factor to determine the performance of LED color, brightness, life and so on. The substrate material surface roughness, thermal expansion coefficient, thermal conductivity coefficient, the influence of polarity, surface processing requirements and epitaxial materials between crystal lattice, and these factors are closely related to the high brightness LED light emitting efficiency and stability. Therefore, the substrate material is the cornerstone of the development of the semiconductor lighting industry, the technical route of the substrate material will affect the entire industry's technical route, is the key to the whole industry chain.

At present, semiconductor lighting has three main routes, respectively with Nichia chemical as the representative of the sapphire substrate LED technology roadmap, represented by CREE of the United States of the silicon carbide substrate LED technology roadmap, and to Chinese latticepower as the representative of the silicon substrate LED technology roadmap. In January 8, 2016, Jiang photoelectric team "high efficiency silicon substrate GaN based blue light-emitting diode technology project won the 2015 National Science and Technology Award technology invention award only can Nanchang University crystal, LED industry China core dream is excited again. Silicon substrate technology project award, indicating that the silicon substrate has been confirmed by the state feasible, and has been promoted to the national strategic level. Silicon substrate or will usher in large-scale commercial applications.

Figure 1 LED substrate materials market share (source: YOLE, CITIC Securities Research and Development Department)

Sapphire (Al2O3) substrate

The Royal Swedish Academy of Sciences announced in October 7, 2014: Akasaki Yong, Tian Hao Hao and Nakamura Shuji won the 2014 Nobel prize in physics for the invention of "efficient blue light-emitting diode". The outstanding contributions of the 3 scientists in 1993, they broke through the system of core technology by high efficiency GaN based blue LED on sapphire substrate. Over the past 20 years, the GaN based blue light LED technology and the rapid development of the industry, based on the sapphire substrate, occupy more than 90% of the market share of the substrate market.

Sapphire has excellent optical properties, mechanical properties and chemical stability, high strength, hardness, erosion resistance. As a substrate material, sapphire has the advantages of good chemical stability at high temperature (2000 DEG C), visible light absorption, low price and so on.

The sapphire substrate also has disadvantages, such as: first, stress mismatch will lead to a large number of defects in the epitaxial layer lattice mismatch and thermal, also caused difficulties in the follow-up processing device; the second, sapphire is an insulator, the resistivity is very large, can not be made device of vertical structure; third, usually only in the epitaxial layer on the surface of production N type and P type electrode, resulting in the effective emission area to reduce, reduce the utilization rate of materials; fourth, sapphire hardness is very high, second only to diamond, it is difficult to thinning and cutting; fifth, the thermal conductivity of sapphire is not very good, so in the use of LED devices, will be sent out a lot of heat on the area large power devices, the thermal conductivity is a very important consideration.

The technical development of the sapphire substrate is relatively mature, although a lot of problems, but have been overcome one by one, for example: the transition layer growth technology overcomes the large lattice mismatch problem; the ipsilateral P and N electrodes to overcome the problem of poor conductivity; difficult problems can be solved by cutting with laser scribing machine; due to the epitaxial layer of the heat stress due to the mismatch can also be solved. However, Jiang believes that the sapphire substrate is difficult to achieve 8 to 12 inches large size extension, and because the sapphire heat performance is poor, and difficult to peel the substrate, it has performance limitations in high power LED.

The sapphire substrate technology with Nichia, TOYOTA as the representative of synthesis. In sapphire crystal and wafer preparation, foreign countries are mainly concentrated in Japan, the United States, Russia and other countries, in 2010 Russia's first exhibition of 200 mm sapphire wafer. There is a big gap between the foreign relative to China, representatives of enterprises of science and technology, electronics, fan Yuan Xin photoelectric, Chongqing Silian optoelectronic semiconductors, such as red, GA. In the extension, in addition to the Tsinghua University, Peking University, Nanchang University, China, Institute of semiconductors and other research units, Sanan optoelectronics, HC semitek, Shanghai north, Nanchang Blue Yan Lei optoelectronics, Jiangxi LIAN photoelectric enterprises in the production and research of epitaxial wafer.

Sapphire material production capacity is currently excessive, low-end market competition. To extend the LED industry chain, should be a high starting point to promote the development of sapphire substrate. Focus on the development of nano patterned sapphire substrate (PSS), hemispherical and conical patterned substrate, and laser induced wet etching (LIBWE), dry etching technology. At the same time, to promote the development of sapphire substrate lithography and etching and related testing equipment, materials, etc..

Silicon carbide (SiC) substrate

SiC has excellent thermal, mechanical, chemical and electrical properties, but not one of the production of high temperature, high frequency and high power electronic devices the best material, and can be used as a substrate material of GaN based blue light emitting diode, breaking the monopoly of the sapphire, especially has a huge market potential in the field of lighting and outdoor lighting. The most commonly used SiC in the semiconductor field is 4H-SiC and 6H-SiC two.

Silicon carbide and sapphire compared to the structure, the sapphire is not a semiconductor but an insulator, it can only do a single electrode; silicon carbide is a conductive semiconductor,