At present, the world's leading companies in the development of GaN-based high-brightness LEDs and semiconductor all-solid-state lighting sources are: Lumileds, HP/Agilent and Cree in the US, Nichia, ToyodaGosei, Sony, Toshiba and other comprehensive in Japan. Large companies (such as NEC, Matsushita, Mitsubishi and Sumitomo, etc.), Osram in Germany, etc. Most of these multinational companies have original patents that lead the trend of technology development and occupy the vast majority of market share. Some photovoltaic companies in Taiwan Province of China (such as Guolian Optoelectronics, Guangbao Electronics, Guanglei Technology, Yiguang Electronics, Dingyuan Optoelectronics, etc.) and some R&D units in Korea also have their own downstream processes and packaging as well as upstream material extension. A number of independent intellectual property rights have a certain market share.
According to the survey, Nichia, Cree, Lumileds, OSRAM, Toyoda Gosei, Toshiba and Rohm, which occupy the majority of the market, have 80% to 90% of original invention patents in the field (focusing on material growth, device fabrication). Most of the rest of the companies have utility model patents (mainly for device reliability and product application development).
Material basis: technical route convergence
The study of GaN-based wide-bandgap semiconductor materials began in the 1960s and 1970s, but compared to other traditional III/V compound semiconductors (such as GaAs-based and InP-based materials), commercialization was applied in the early 1990s. It was realized in the medium term, so there are still many problems related to the research of its basic physical/chemical properties. In these respects, some famous universities and research institutions in the United States, Japan, South Korea and Europe enjoy research reputations. These academic units are conducting various industrial technology research (based on MOCVD metal organic chemical vapor phase epitaxy) with cooperative enterprises. The basic physical/chemical properties of GaN-based materials are also studied by techniques such as RS-MBE (Radio Frequency Source Molecular Beam Epitaxy).
We have published statistics on academic papers published in the Journal of Crystal Growth and Applied Physics Letters, which were published in the past 10 years from 1993 to 2002. In the 877 research papers on GaN light-emitting devices surveyed, about 60% of the experimental samples (531 related papers) were obtained by epitaxial growth of MOCVD technology, and the remaining 40% of the experimental samples were RS-MBE. Obtained by other technical means such as HVPE.
It can be seen that, for the entire global industry, the technical route based on MOCVD epitaxial growth is the main technical trend of developing GaN-based optoelectronic materials and devices, and the technical routes such as RS-MBE are more suitable for basic academic research work. Therefore, this patent investigation report is mainly aimed at MOCVD epitaxially grown GaN materials.
Compared with blue-green light-emitting devices made of SiC, ZnS and other II/VI compound semiconductor wide-bandgap materials, GaN-based devices have long life, high luminous efficiency and relatively low price, and are recognized as all-solid-state lighting sources. The material of choice for die devices.
Epitaxial technology: the focus of competition
In general, epitaxial growth of GaN-based materials is the core technology for the development of GaN-based high-brightness LEDs and all-solid-state semiconductor white light illumination sources. It is the top priority of all key problems, so a large number of patents have been applied on this issue. Such as high-quality GaN epitaxial growth equipment (US5433169, EP0887436), substrate pretreatment technology (JP7142763), buffer layer technology (JP2000124499 with AlN, JP7312350 with GaN, EP1111663 with SiNx), multi-buffer layer technology (US6495867), Superlattice blocking dislocations (US2001035531), lateral epitaxial overgrowth techniques (EP0942459), and hanging epitaxial techniques (US6285696) and the like are employed.
We will outline the development of the technology in general. First, Nichia Corporation pioneered the patent for a dual-beam MOCVD system (US5433169). Due to the emergence of this new MOCVD system, the quality of MOCVD-grown GaN material crystals has been greatly improved.
Secondly, the emergence of buffer layer technology solves the problem of large lattice mismatch and thermal mismatch in the growth of GaN materials on heterogeneous substrates. Since the GaN material grown under the buffer layer technology still has a high defect density, which affects important technical indexes such as luminous intensity, working life and reverse characteristics of the light-emitting device, people have developed multi-buffering on this basis. Layer technology to obtain higher quality GaN single crystal materials.
At this point, GaN materials are sufficient to meet the needs of general high-brightness LED device fabrication, but to make GaN-based blue/green laser diodes on this basis, the defect density of GaN-based materials must be further reduced. The subsequent ELOG (Epitaxy of Lateral Over-growth) and suspension epitaxial techniques were proposed to solve this problem. Of course, the epitaxial optimization technology represented by this ELOG is relatively expensive, and the GaN epitaxial material used for making high-power illumination die devices does not need to adopt this technical route, but its design idea is worth learning from, that is, the largest Limitly try to reduce the defect density in the epitaxial material and improve the overall performance of the device.