Semiconductor lighting, often referred to as the third generation of lighting technology, has found extensive applications in large-screen color displays, special lighting, traffic signals, LCD backlights for multimedia displays, and optical communications. As a cold light source, it is environmentally friendly and offers energy efficiency that exceeds 90% compared to traditional incandescent and fluorescent lamps. This makes it an attractive solution for sustainable lighting.
In the industry, semiconductor lighting is commonly known as LED technology, which includes core LED technology, packaging technology, and application technology. In recent years, with strong support from various countries, LED chip technology has advanced rapidly, leading to larger chip sizes and higher power outputs. A single LED chip can now be used in high-power installations, such as 3W LEDs. The design and functionality of packaged products have also evolved, offering greater flexibility and diversity in LED lighting solutions.
Several countries, including the United States, Japan, and South Korea, have launched national initiatives to promote semiconductor lighting. Major global lighting companies like General Electric, Philips, and Osram have partnered with semiconductor firms to develop new lighting technologies. In the U.S., the Department of Energy and the Optoelectronics Industry Development Association supported Sandia National Laboratories in drafting a long-term plan (2002-2020) for semiconductor lighting, aiming to shape the future of illumination through technological innovation.
Japan has also invested heavily in this field through the “Japan 21st Century Lighting Project,†organized by the Japan Research and Development Center of Metals and NEDO. This five-year initiative involved universities, companies, and associations, aiming to improve energy efficiency using GaN-based blue and ultraviolet LEDs. The project aimed to double the efficiency of traditional fluorescent lamps, reduce energy consumption, and lower CO₂ emissions, with a total budget of 6 billion yen.
The most widely researched semiconductor lighting technology today involves III-nitride light-emitting diodes, such as InGaN, AlGaN, and GaN. These devices emit blue-green, blue, and ultraviolet light, which can be combined with red and green LEDs to produce white light. They can also directly excite phosphors to generate white light. As a result, nitride LEDs are considered the preferred choice for white light sources and are expected to replace traditional lighting technologies in the future.
Over the past few decades, the luminous efficiency of LED devices has increased tenfold every decade. In particular, GaN-based blue-green LEDs, which emerged in the early 1990s, have seen their efficiency increase by a hundredfold in just 10 years. This breakthrough enabled full-color LED displays and made LED-based white lighting possible. With advancements in material growth and fabrication techniques, LEDs have evolved from low-power indicators (typically 20 mA injection currents) to high-power types (now around 350 mA), expanding their applications from simple indicators to complex systems like traffic signals, car lighting, and large-scale displays.
GaN-based power blue LEDs are considered the third-generation lighting source, following incandescent and fluorescent lamps. Compared to traditional light sources, they offer advantages such as high efficiency, long lifespan, compact size, fast response, vibration resistance, environmental friendliness, and safe operation. Their potential for widespread use in energy-saving lighting is significant.
At the heart of semiconductor lighting is the light-emitting diode (LED). When forward-biased, electrons are injected into the active region of the pn junction, where they recombine and emit light. Since the 1950s, the wavelength of LEDs has expanded from infrared to visible and ultraviolet ranges. The emission wavelength depends on the bandgap energy of the semiconductor material. Gallium nitride-based LEDs, which are direct bandgap materials, include compounds like aluminum nitride (AlN), indium nitride (InN), and gallium nitride (GaN), covering visible, ultraviolet, and deep ultraviolet bands.
There are three main methods to achieve semiconductor lighting:
1) Using red, green, and blue LEDs to mix and create white light (Figure 2a).
2) Exciting trichromatic phosphors with ultraviolet LEDs to produce white light (Figure 2b).
3) Using blue LEDs to excite yellow phosphors to create a binary white light mixture (Figure 2c).
Mixing three primary color LEDs allows for an ideal white light spectrum and adjustable color temperature, though it requires precise performance and complex driving circuits, making it more expensive but suitable for high-color-quality applications. UV LED excitation of phosphors is still limited due to the lack of high-power UV LEDs and efficient UV phosphors. However, the third method—using blue LEDs to excite yellow phosphors—is currently the most mature and widely used approach, offering high lumen efficiency, even though its color rendering index may be slightly lower. Unless otherwise stated, semiconductor lighting typically refers to this method.
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