1 Introduction
LED has been in development for nearly 30 years. In the 1970s, the earliest GaP, GaAsP homogeneous red, yellow, and green low-luminance LEDs began to be used for indicator, digital, and text displays. Since then, LEDs have entered a variety of applications, including aerospace, aircraft, automotive, industrial applications, communications, consumer products, etc., throughout the national economy and thousands of households. By 1996, LED sales worldwide had reached billions of dollars. Although LEDs have been limited by color and luminous efficiency for many years, GaP and GaAsP LEDs have been favored by users because of their long life, high reliability, low operating current, compatibility with TTL and CMOS digital circuits. .
In the last decade, high brightness and full colorization have been the frontier topics in the research of LED materials and device technology. Ultra High Brightness (UHB) refers to LEDs with luminous intensities up to or exceeding 100mcd, also known as Candela (cd) grade LEDs. The development of high-brightness A1GaInP and InGaN LEDs has progressed very rapidly, and has reached the performance level that conventional materials GaA1As, GaAsP, and GaP cannot achieve. In 1991, Toshiba and the United States HP developed InGaAlP 620nm orange ultra-high brightness LED. In 1992, InGaAlP 590nm yellow ultra-high brightness LED became practical. In the same year, the normal light intensity of InGaA1P 573nm yellow-green ultra-high brightness LED developed by Toshiba was 2cd. In 1994, Nichia Corporation developed InGaN 450nm blue (green) color ultra-high brightness LED. At this point, the three primary colors of red, green, blue, and orange and yellow LEDs required for color display have reached the candela-level luminous intensity, achieving ultra-high brightness and full color, and making the outdoor full color of the luminous tube. The display becomes a reality.
China's development of LED started in the 1970s and formed an industry in the 1980s. There are more than 100 enterprises in the country, and 95% of the manufacturers are engaged in post-package production. The required dies are almost all imported from overseas. Through several "five-year plan" technical transformation, technical research, the introduction of foreign advanced equipment and some key technologies, China's LED production technology has taken a step forward. Some manufacturers in Beijing, Changchun, Nanchang, Shanghai, Shandong, Hebei and other places now have mass production capacity of GaAs and GaP single crystals, epitaxial wafers and chips. The Puliang LED chip production line of Xinlei Optoelectronics Co., Ltd., which was established by Nanchang 746 Factory, produced 700 million cores in 1998 and more than 1 billion in 1999. Hebei Huiyou Power Electronics Co., Ltd. and Hebei Lide Electronics Co., Ltd., affiliated to the 13th Research Institute of the Ministry of Information Industry, have completed the InGaA1P ultra-high brightness LED epitaxial wafer and chip production line respectively. By the end of 1999, the company has reached an annual output of 10,000 pieces of epitaxial wafers and chips. The production capacity of 100 million has changed the situation that China's ultra-high brightness LED epitaxial wafers and chips are all imported from overseas.
This article will give a brief introduction to the application of ultra-high brightness InGaA1P LEDs and InGaN LEDs in automotive indicator lights, traffic lights, large-screen displays, and backlighting of liquid crystal displays (LCDs).
2 Ultra-high brightness LED structure and performance
Ultra-high-brightness red A1GaAs LEDs have higher luminous efficiency than GaAsP and GaP LEDs. The lumen efficiency of transparent substrate (TS) A1GaAs LEDs (640nm) is close to 10lm/W, which is 10 times larger than red GaAsP-GaPLED. Ultra-high brightness InGaAlP LEDs provide the same color as GaAsP and GaP LEDs, including green-yellow (560nm), light green-yellow (570nm), yellow (585nm), light yellow (590nm), orange (605nm), light red (625nm), Dark red (640nm). The InGaAlPLED absorption substrate (AS) has a lumen efficiency of 101m/W, a transparent substrate (TS) of 201m/W, and a lumen efficiency of 10 to 20 times higher than the GaAsP and GaP LEDs in the wavelength range of 590 nm to 626 nm; It is 2 to 4 times higher than the GaAsP and GaP LEDs in the wavelength range of 560 nm to 570 nm. Ultra-bright InGaN LEDs provide blue and green light in wavelengths from 450nm to 480nm for blue, 500nm for blue-green, and 520nm for green, and lumens efficiency of 3m/W to 151m/W. The current lumen efficiency of ultra-high-brightness LEDs has surpassed that of incandescent lamps with filters, which can replace incandescent lamps with a power of less than 1W, and LED arrays can replace incandescent lamps with a power of less than 150W. For many applications, incandescent lamps use filters to get red, orange, green, and blue, while ultra-high brightness LEDs give the same color. In recent years, ultra-high-brightness LEDs made of AlGaInP materials and InGaN materials have combined multiple (red, blue, green) ultra-high-brightness LED chips, and various colors, including red, orange, and yellow, can be obtained without filters. , green, blue, the current luminous efficiency has exceeded the incandescent lamp, the positive fluorescent lamp is close. The brightness of the light has been higher than 1000mcd, which can meet the needs of outdoor all-weather and full-color display. The LED color large screen can express the sky and the ocean to realize three-dimensional animation. A new generation of red, green and blue ultra-high brightness LEDs has achieved unprecedented performance.
3 ultra-high brightness LED application
3.1 Information indicator
3.1.1 Car signal indication
The car lights are mainly the direction lights, tail lights and brake lights on the outside of the car; the interior of the car is mainly the illumination and display of various instruments. Ultra-high-brightness LEDs are used in automotive lights and have many advantages over traditional incandescent lamps, with a broad market in the automotive industry. LEDs are able to withstand strong mechanical shocks and vibrations. The average working life (MTBF) is orders of magnitude higher than that of incandescent bulbs, far higher than the working life of the car itself, so the LED brake lights can be packaged as a whole without having to consider repairs. Transparent Substrates AlGaAs and AlInGaP LEDs have a relatively high lumen efficiency compared to incandescent bulbs with filters, so that LED brake lamps and directional lamps can operate at lower drive currents. Typical drive currents are only incandescent. 1/4 of the light. The lower power also reduces the size and weight of the car's internal wiring system, while also reducing the internal temperature rise of the integrated LED beacon, allowing the lens and housing to use low temperature resistant plastic. The response time of the LED brake light is 100 ns, which is shorter than the response time of the incandescent lamp, which leaves the driver with more reaction time, thus improving the safety of the driving. The illuminance and color of the exterior lights of the car are clearly defined. Although the interior lighting display of a car is not controlled by the relevant government departments like an external signal light, the manufacturer of the car has requirements for the color and illumination of the LED. GaP LEDs have long been used in the car, and ultra-high-brightness AlGaInP and InGaN LEDs will replace the incandescent lamps in the car because they meet the manufacturer's requirements in terms of color and illumination. From the price point of view, although LED lights are more expensive than incandescent lamps, the price of the two systems is not significantly different from the overall system. With the development of practical applications of ultra-high brightness TSAlGaAs and AlGaInP LEDs, prices have been decreasing in recent years, and the reduction will be even greater in the future.
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