Dilute ferromagnetic nitrides by red LED revolutionon January 12th, 2012 at 2:01 AM
Red, orange and light yellow dilute magnetic nitride LED with a higher power and lower temperature sensitivity. Take the traditional red AlGaInP LED and new InGaNP LED for comparison and found the latter more brightness, suitable for big screen color display backlight unit.
Participation in the general lighting market competition, the blue and white LED performance has been a huge increase, which is used in large color screen, traffic lights and architectural lighting field of red, amber and yellow LED in sharp contrast, the latter performance is slow.
However, just a University of California, San Diego (UCSD) isolated the new company Quanlight, has developed a completely different chip manufacturing process, it can overcome these obstacles and greatly improve the performance of LED. By replacing the traditional material of AlGaInP new dilute magnetic nitride materials InGaPN, it is possible to prepare a high-brightness LED, and its not very sensitive to temperature changes. This will output that require stable, high-quality images, the red light helpful for large-screen color display applications.
The traditional red LED has been used in car brake lights, when turned on InGaPN device after the lights brightness is improved, the number of devices needed to be reduced. Source: BMW’s
The core of this key technology from the University of California, San Diego (UCSD) research results. Charles Tu led by the UCSD team, before the company was founded in Quanlight in InGaPN made some progress. This material contains about 1% of nitrogen, the red LED appears to be an ideal alternative material. InGaPN and GaP, once combined, can produce more than the AlInGaP-based LED heterojunction band difference. Calculations show that the larger the current handling capacity because it can produce a higher brightness of the LED. In addition, although this material system is not yet mature, little is known about it and difficult to grow, InGaPN already have some exciting preliminary results.
The UCSD researchers have sought to design an effective prototype LED, the device performance, as expected, as implemented in several improvements, including reducing the emission wavelength with temperature drift size. Although initial research for these devices is sufficient, but with the MBE equipment contaminated materials, this limits the brightness of the LED. Therefore, further development work needs to turn to commercial production plant, and the use of technology and equipment which is based on MOCVD platform.
Commercialization of academic research
To this end we have created Quanlight company, and formed a R & D team. Raised from private investors made two funds totaling $ 4,000,000, in early August 2006 we Bandwidth Semiconductor wafer foundry services to develop, good progress is being made, and late last year and sold in accordance with plans to build Red LED epitaxial wafers to chip manufacturers. Now we plan to extend the scope of the wafer to cover 585nm to 660nm orange and yellow bands. In addition, we also began to license proprietary technology, or partnerships with other companies.
InGaPN LED relative to the AlGaInP LED has three main advantages: lower manufacturing costs, better color temperature stability and high current, high brightness.
Lower manufacturing costs from a more streamlined manufacturing processes, production equipment it uses consistent with the traditional red LED. Traditional AlInGaP-based LED is grown on the GaAs substrate, in order to enhance the output power, the wafer is typically placed in a transparent GaP substrate or mirror support body. Our process dilute magnetic nitride can grow directly on the GaP substrate, which reduces the traditional production of the required “epitaxial layer removal and bonding” two process steps; thereby reducing material costs.
In our devices, GaP substrate and InGaPN materials lattice mismatch between the small, which means that the wafer is the pseudo-potential response, but it allows the integration of the LED quantum well enough to achieve high-power the output. The resulting structure of its quality and grown on the GaAs substrate AlInGaP material similar to, but the drawback is the market does not provide vertical gradient condensation method (VGF) preparation of GaP substrate. VGF is a very low dislocation density can grow boules of the manufacturing process.
Improve the quality of GaP
Figure 1. Quanlight of 635nm LED compared to traditional design, it’s less affected by temperature, better stability.
We now use the 3 “substrate with liquid seal Czochralski (LEC) growth process, which applies to the LED production, from the device brightness and reliability with business competitiveness. And PVA TePla We are also co-develop new technologies, prepared using the VGF GaP boules. We hope that this venture will be successful, because the VGF method is well known in the industry, and other materials has long been used to grow a substrate. Although the switch can not predict how much can the VGF material after profits, but we expect it to improve InGaPN based LED life and power output. We have already started the initial measurement of the system on this platform to take the LED, and hope in a very short period of time can be achieved initial results.
InGaNP the intrinsic properties of the device to ensure that the peak wavelength with temperature drift will be less than AlInGaP devices. For those who need a stable light source applications such as color displays, light emitting devices more attractive. Laboratory at UCSB, we found by MBE method into its red LED color stability has been improved, but this is the LED by MOCVD as equally effective. By external heating of the LED temperature from 25 ℃ to 125 ℃, and recorded at different temperatures peak emission wavelength. Test results shown in Figure 1, LED peak emission wavelength in the entire temperature range just changed 3nm, red light relative to the leading LED manufacturer produced AlInGaP chip, 3nm offset only one-fifth of the latter one.
InGaPN LED third advantage is the high temperature glow brighter, which originated from a superior band structure, the active region can improve the carrier confinement effect. With GaP barrier InGaPN LED produced a larger band offset, usually AlGaInP AlGaInP quantum well and barrier band offset of 2-3 times.
At 25 ℃ to 125 ℃ range, by comparing the Quanlight LED and conventional red LED output power, the results validate the performance of the former is stronger at higher temperatures (Figure 2).
Quanlight device 125 ℃ when the transmit power is that it at 25 ℃, 48%, but the only reference to the LED 25% of its initial value. When we have completed the research and development of device technology, the hope that our materials can be prepared at room temperature and the same bright AlInGaP chip devices, and more than 150 ℃, high-brightness AlInGaP chip is about 2 times. At high temperatures InGaNP LED’s performance has been improved, the characteristics of red and yellow traffic lights more attractive. They melt in the United States the minimum standard is 25 ℃ and 74 ℃.
Active region in the enhanced carrier confinement also good current handling, during the research phase of the test devices have been produced up to 9A/mm2 current density (Figure 3). These tests are conducted on the wafer, instead of chips for each gash conducted. It is reasonable to predict a new generation of products will lower the effective parameters. Nevertheless, we can predict the saturation current density InGaPN LED AlInGaP based on similar products is 2-3 times.
Figure 2 higher temperatures 635nm LED output power in the attenuation, the amplitude as the carrier confinement increases gently. AlInGaP LED data from one of the leading LED manufacturer.
Shift from the traditional red-chip devices InGaPN three advantages: higher current handling capability of the LED packaging and application engineers to help; in a larger drive current use of smaller devices, and can give the same amount of light; or less can be used in high-power array of large-size LED. These methods are able to reduce the LED size and reducing the overall cost, whether it is more a small LED or the same number of LED, the total cost because of small size and more expensive LED.
We are now testing the reliability of this red LED, will develop a device to be 5,000 hours of testing; We also plan to compare the growth of LEC and VGF methods substrate made of LED performance.
Ready to start
We have transferred the device to the MOCVD growth of the platform, and using the most optimized epitaxial layer design. Observed from our device to increase the light output. Nitride and dilute the intrinsic magnetic properties of the, we do not damage the color light-emitting devices and thermal stability can get the advantage.
While we may think many areas of diluted magnetic nitride is a material difficult to understand, not in the telecommunications sector to play its due role. We have reason to believe that this device will be a commercial success. Dilute magnetic nitride epitaxial layer communications lasers require high concentrations of indium content, an increase of material and reduce the stress of life and reliability of the device. But the red, orange and yellow InGaPN LED indium containing a very small, it will not have this problem.
Figure 3. Quanlight LED was able to withstand very high current density, unlike traditional LED can only be issued only in 2.0A/mm2 the following peak brightness; tested on the wafer, which InGaNP LED will be issued in the two brightest light : 300 × 300 μm, if the chip, the current density is 9.0A/mm2; 400 × 400 μm, if the chip, the current density of 5.5A/mm2.
We are in the preparation of dilute magnetic nitride obtained a wealth of experience, compared to other may be preparing to develop products based on this material company, which earned us a strong competitive edge. Although in the Bandwidth Semiconductor wafer growth, but we will process knowledge and intellectual property in their own hands, all the technical team involved in the development of on-site growth process. The team led the development of this material.
When we start the more combination products, such as covering 585nm to 660nm high-power red, brown and yellow LED epitaxial wafers, we have entered a target of $ 500 million fast-growing market of high brightness. Performance advantages of our products will fit needs of high and stable color output applications. LED chip to reduce the temperature-induced wavelength shift, so that LCD TV backlight unit, the projector’s light engine, outdoor displays and other applications benefit from the RGB color mixing, that displays the control mechanism has been simplified. Also, this section of the new high-intensity red LED output is also suitable for use in transport, dangerous land, buildings and other aspects of theater and lighting.
Such as traffic lights and automobile brake lights AlInGaP LED applications to reduce energy use and costs for this type of high-power applications, InGaPN LED enables engineers to design more and low-cost lighting, the reason mentioned earlier: in the higher The current use of a smaller size of the chip, or array to use fewer large-size LED. As Quanlight LED at high temperatures to work effectively, you need to use a more compact structure or shell can enhance heat dissipation.
In the absence of strict standards of low output power applications, such as Christmas tree lighting, which InGaPN LED superior in terms of not only where there is no current Quanlight aggressive low-power applications of this market, because low-cost low-power AlInGaP chip has been widely supplied.