|
 |
 |
|
|
|
 |
|
|
The achievement honored is the development of blue light emitting semiconductor devices, the blue light emitting diode (LED) and the blue laser diode (LD), which complete the light spectrum for semiconductor devices.
Light emitting devices have many useful applications in daily life. The completion of the light spectrum, enabled by the invention of the blue LED, has resulted in the development of large, outdoor, full-color displays on building walls, which are clear and easy to see even in bright sunlight. Traffic signals have also been developed using semiconductor LEDs. Compared to conventional incandescent bulb-based traffic signals, these new traffic signals have improved visibility, lower electric power consumption and a longer lifespan. Thirdly, combining the blue LED with fluorescent material has resulted in the creation of white LEDs, which have been used to backlight displays in mobile phones. In the future, it is believed that the white LED will replace conventional lamps for lighting homes and offices. The replacement of conventional lamps with LEDs is expected to reduce electric power consumption, due to the high efficiency of LED light emission, and to reduce waste because of the longer lifespan of LEDs.
The blue LD will also enable a new generation of DVDs and CDs with more than a six-fold increase in optical storage capacity. Photographs and moving pictures, including animation, can be easily recorded, manipulated, stored, and carried as digital data using blue LD-based devices. Image projectors using laser light are also expected.
The development of blue light emitting semiconductor devices involved many challenges. Akasaki and Amano, and Nakamura, respectively, succeeded in overcoming these challenges through highly creative approaches within the same time frame.
Akasaki was confident that gallium nitride (GaN) would be the best material with which to make blue light emitting semiconductor devices, although the majority of researchers were using zinc selenide (ZnSe). Akasaki and Amano fabricated GaN film with good crystal quality and uniform thickness on an aluminum nitride (AlN) buffer layer grown on a sapphire substrate. Then, they fabricated a p-type GaN layer with high conductivity by using electron beam irradiation on a p-type impurity doped GaN thin film. In 1989, they developed a p-n junction blue LED in their laboratory. Regarding blue LD development, they observed emission of strong light with a narrow bandwidth, and it was reported in November 1995.
Nakamura also chose to work with GaN, rather than with ZnSe used by the majority of researchers. He invented film deposition equipment with a unique two-flow method, and fabricated GaN film with good crystal quality and uniform thickness. He achieved high conductivity, p-type GaN by heat treatment in the atmosphere without hydrogen. He developed a high brightness blue LED of double heterostructure using In-doped GaN layer in 1993. Regarding blue LD development, he succeeded in achieving laser oscillation, introducing a multi-quantum well structure with several tens of In GaN layers and a blocking layer, and reported this in January 1996. Based on these achievements, the blue LED was introduced in 1993 and the blue LD was introduced in 1999. Those were the first blue LED and blue LD commercialized products in the world.
Akasaki and Amano and Nakamura overcame difficult challenges that required a creative approach. Moreover, they contributed to the commercialization of blue LD and LED-based devices. The Takeda Award 2002 for Social/Economic Well-Being is awarded to this techno-entrepreneurial achievement that embodies engineering intellect and knowledge, and enables many applications in human life that will expand the wealth, richness, and happiness of people.
|
|
|
