The future of purple LED chip LED lighting will focus on research
At the end of the last century, semiconductor lighting began to develop and rapid development, one of the core premise is the growth of Blu-ray GaN-based luminescent materials and device structure, and the future level of material and device structure technology will eventually determine the height of semiconductor lighting technology. The GaN-based materials and devices derived from the equipment, source materials, device design, chip technology, chip applications and other five parts of the analysis.
In the case where large-scale GaN single crystal materials can not be prepared at present, MOCVD is a metal organic chemical vapor deposition device which is still the most critical device for GaN heteroepitaxy. The current commercial MOCVD equipment market mainly by the two international giants to master, in this situation China MOCVD still made great development, and the emergence of 48 machines.
But we still need to recognize the shortcomings of the domestic MOCVD. For MOCVD, in general, the focus of research-based equipment is temperature control, commercial equipment is uniform, repeatability and so on. At low temperature, high In composition can grow high InGaN, suitable for nitride system materials in orange yellow, red, infrared and other long wavelength applications, so that nitride applications cover the entire white light field; and 1200oC-1500oC high temperature, can grow High Al composition of AlGaN, nitride applications extended to the field of ultraviolet and power electronic devices, the scope of application to obtain greater expansion.
At present, foreign countries already have 1600oC high temperature MOCVD equipment, can produce high-performance UV LED and power devices. China MOCVD still need long-term development, to expand the MOCVD temperature control range; for commercial equipment not only to improve performance, but also to ensure uniformity and scale.
The source material mainly includes various kinds of gas material, metal organic material, substrate material and so on. Among them, the substrate material is the most important, directly restricting the quality of epitaxial film. At present, GaN-based LED substrate more and more diversified, SiC, Si and GaN and other substrate technology gradually increased, part of the substrate from 2 inches to 3 inches, 4 inches or even 6 inches, 8 inches and other large size development.
But the overall point of view, the current cost-effective is still the highest sapphire; SiC superior performance but expensive; Si substrate prices, size advantages and the convergence of traditional integrated circuit technology makes the Si substrate is still the most promising technology route one.
GaN substrates still need to improve the size and reduce prices in terms of efforts in the future in the high-end green laser and non-polar LED applications to show their talents; metal organic materials from dependence on imports to independent production, with great progress; other gases Materials have made great progress. In short, China has made great progress in the field of source materials.
The extension, that is, the process of obtaining the device structure, is the most technically technically necessary process to directly determine the internal quantum efficiency of the LED. At present, most of the semiconductor lighting chip using multi-quantum well structure, the specific technical route is often subject to the substrate material. The sapphire substrate commonly used graphics substrate (PSS) technology to reduce the epitaxial film for the wrong density to improve the internal quantum efficiency, but also improve the efficiency of light out. Future PSS technology is still an important substrate technology, and the graphics size gradually to the direction of nano-development.
The use of GaN homogeneous substrate can be non-polar or semi-polar surface epitaxial growth technology, part of the elimination of polarized electric field caused by the quantum Stark effect, in the green, yellow-green, red and orange GaN-based LED applications with Very important meaning. In addition, the current epitaxy is generally the preparation of single-wavelength wavelength quantum wells, the use of appropriate epitaxial technology, can be prepared multi-wavelength emission of LED, that is, single-chip white LED, which is one of the promising technical route.
Among them, representative of the InGaN quantum well with the separation, to achieve a high In composition of InGaN yellow quantum quantum dot and blue light quantum combination of white light. In addition, the use of multiple quantum wells to achieve wide spectral light emission mode, in order to achieve single-chip white light output, but the white color rendering index is still relatively low. Non-fluorescent single-chip white LED is a very attractive direction of development, if you can achieve high efficiency and high color rendering index, will change the semiconductor lighting technology chain.
In the quantum well structure, the introduction of electron blocking layer to block the electronic leakage to improve the luminous efficiency has become a conventional method of LED epitaxial structure. In addition, the optimization of the potential barrier and potential well of the quantum well will continue to be an important process link, how to adjust the stress, to achieve band cutting, you can prepare different wavelengths of LED light. In the chip cover layer, how to improve the p-type layer of material quality, p-type hole concentration, conductivity and solve the high current droop effect is still a priority.
In the chip technology, how to improve the efficiency of light extraction and get a better cooling solution to become the core of the chip design, and the corresponding development of the vertical structure, surface roughening, photonic crystal, flip structure, film flip structure (TFFC), new Transparent electrodes and other technologies. Among them, the film flip-chip structure using laser stripping, surface coarsening and other technologies, can greatly improve the efficiency of light.
White LED for Blu-ray LED Excited Yellow Phosphor Low Technical Solution Low RGB conversion efficiency, RGB multi-chip white and single-chip phosphor-free white light as the main trend of future white LED, low-efficiency green LED Become the main limiting factor of RGB multi-chip white light, the future semi-polar or non-polar green LED will become an important development trend.
In the solution of white LED color, you can use purple or UV LED excitation RGB three-color phosphor, high-color white LED technology, but must sacrifice part of the efficiency. At present, the efficiency of violet or ultraviolet chip chip has made great progress, Nichia Chemical Company produced 365nm wavelength UV LED external quantum efficiency is close to 50%. The future of UV LED will be more applications, and no other UV light system materials instead, the development prospects are enormous.
Some developed countries have invested a lot of manpower, material resources to carry out UVLED research. The nitride infrared light band applications, in addition to the environment, both the price or performance are difficult to compete with arsenic, and thus the prospects are not very clear.
According to the above, it can be seen that the upstream materials and equipment surrounding semiconductor lighting have been greatly developed, especially in terms of efficiency, the blue band is close to the ideal efficiency, the chip in the semiconductor lighting price ratio is also significantly reduced, the future of semiconductor lighting from the light The efficiency of the development of light quality, which requires chip materials to break through the field of blue light, while the long wavelength and short wavelength direction, and green, purple and UV LED chip will be the focus of future research.