Nanotechnology challenges the technical issues of high-brightness LEDs

High-brightness LEDs have encountered some technical challenges in the process of mass production with high quality and low cost, which creates good opportunities for breakthrough solutions, especially for those startups with "breakthrough thinking" who are trying some interesting nanotechnology solutions. The important aspects of innovation are materials, quantum dots and confined crystal structures in substrates may have the potential to achieve higher efficiency and lower cost. Of course, some more mature companies also have some breakthrough solutions, such as using RF waves instead of visible light waves to test chips and obtain better yield control feedback.

One way to get more of the desired warm white light from high-brightness LEDs is to use quantum dots instead of red phosphors for light conversion. QD Vision says its semiconductor nanocrystals can be tuned to specific narrowband light waves based on particle size and material, increasing the number of lumens per watt of LED light by 30% compared to using phosphor conversion solutions. Lamp manufacturers use quantum dot films to cover LED lamps to fine-tune the color of the light. QD Vision is currently shipping large quantities to lamp manufacturers.

Seth Coe-Sullivan, CTO and co-founder of the company, said that the company is also interested in the LED backlight market and plans to launch related products next year. For backlight products, the coating coated with nanocrystalline ink can be directly used for blue light LEDs to replace phosphors, which can improve display performance and allow more light to pass through, increasing power efficiency by about one third.

Coe-Sullivan claims to have launched a complete line of quantum dots that do not contain cadmium, and that can continuously emit 20-30mW/cm2 of light intensity without variation.

Startup company Jingneng Optoelectronics has produced commercial high-brightness blue LEDs on silicon substrates

Chinese startup Lattice Power (Nanchang, China) is making high-brightness LEDs on silicon substrates, with small blue and green display devices already in mass production, and LCD backlights and general lighting products with large-size chips coming soon.

Its unique technology comes from the scientific research results of Professor Jiang Fengyi and his research team at Nanchang University. Depositing the GaN layer on silicon instead of sapphire or SiC can better control thermal mismatch and lattice mismatch. Lattice has recently obtained some patents and published research progress at some technical conferences. One of its products obtains 100 lumens of cool white light at a current of 350mA from a 1×1mm blue light chip. The substrate is InGaN/GaN deposited on a (111) 2-inch silicon substrate. Researchers said that the results of accelerated life tests showed that the reliability of the product is similar to that of LEDs on sapphire. Lattice Power researchers are also conducting research and development on larger silicon wafers to further improve cost-effectiveness.

The current 200×200μm blue and green chip products are mainly used in large display screens . The company is also promoting the process of using larger chips for high-brightness applications. "We are currently limited by production capacity and are vigorously increasing the capacity of MOCVD ," said Dr. Lu Bo, the company's executive vice president. With the expansion of production capacity, Jingneng Optoelectronics plans to sell blue light chips to packaging manufacturers for LCD backlighting and general lighting.

Inlustra Technologies' non-polarized GaN substrates are ready

UC Santa Barbara's spin-off company Inlustra Technologies is using a modified HVPE chemistry to directly grow non-polarized and semi-polarized GaN substrates, trying to influence the laser and LED substrate fields in different ways. CEO Benjamin Haskell said that 2-inch and 3-inch products have been trial-produced. Samples are still being produced, and mass production is expected to begin in early 2011.

The first applications will likely be green-blue laser diodes, which are difficult to make in the usual crystal orientation and are less price sensitive than lighting. But as volumes grow and prices for these initial applications come down, Haskell expects the technology to bring down costs for solid-state lighting as well . Although the company has reduced the cost of manufacturing GaN substrates by using simplified equipment and reducing material losses, Haskell also stressed that the final device cost will fall even more because making LEDs on GaN simplifies the entire manufacturing process, including epitaxial deposition and device processing. Because efficiency losses are reduced compared to conventional polarized LEDs and light output is increased, LED chips can be made smaller and fewer chips are needed for the same light output.

Haskell said that it is possible to achieve orders of magnitude improvement in performance by non-polarizing GaN devices and substrates because changing the crystal orientation eliminates the effects of the inherent polarization fields of devices (such as current LEDs and LDs) that are perpendicular to the normal crystal orientation. Devices made on the usual crystal plane must overcome these built-in electric fields (on the order of megavolts per centimeter) to turn on the device; efficiency loss and color shift are two negative effects of these electric fields. But if the device is made on a non-polarized surface, this polarity will still remain on the growth plane without negatively affecting performance.

Op-Test seeks better ways to test and track device performance

Op-Test has been working on high-brightness LED test equipment for more than a decade, but recently the company announced that it had to find better ways to test and track device performance. Op-Test uses an energy control test that allows direct measurement of the electrical energy entering the chip and the corresponding output light energy . "We don't have to convert light data, just the emission wavelength information." President Dan Morrow pointed out, "Emission data allows designers to better predict the performance of the chip and design around it. It also provides better feedback to control production uniformity and yield." The system is currently being tested by a customer.