This year’s (2014) Nobel Prize for physics awarded to Isamu Akasaki and Hiroshi Amano of Nagoya University in Japan and Shuji Nakamura of the University of California at Santa Barbara, goes beyond recognising their invention that is of “greatest benefit to mankind”. It befittingly rewards them for their perseverance and tenacity and for daring to “challenge established truths”. With red and green light emitting diodes (LEDs) already available, there were feverish efforts by many industries and institutions across the world to invent a blue LED; a combination of red, green and blue produces white light. But there were almost insurmountable challenges that had to be overcome, and most scientists dropped out of the race midway. The first major practical difficulty to be overcome was growing high-quality gallium nitride crystals using a suitable substrate. Dr. Akasaki and Dr. Amano, who worked as a team, and Dr. Nakamura used diverse approaches to achieve this. The duo finally tasted success in 1986 even as others moved on to different materials; Dr. Nakamura produced it four years later. Since the gallium nitride crystal is by default n-type layer with a surplus of electrons, the laureates had to create a p-type layer (holes that are electron-deficient). Working against all odds, the two teams finally succeeded in creating the p-type layer and hence a blue LED. They also created heterojunctions with multiple layers to improve the efficiency of blue LED.
If the arrival of brighter fluorescent lamps in the 20th century reduced electricity consumption compared with tungsten lamps, the advent of compact fluorescent lamps led to a further substantial drop in electricity consumption. However, LED technology has made all the other lamp technologies redundant with the superior brightness per wattage that it offers; the white light produced by LED has become a game-changer in lighting technology. Unlike the other lighting options, where a certain proportion of the electricity is converted into heat and is wasted, LED technology allows for direct conversion of all electricity into light, thereby increasing efficiency. With nearly 20 to 30 per cent of electricity worldwide being used for lighting, the widespread use of LEDs will lead to significant gains. Besides being energy-efficient, LEDs are environment-friendly as no mercury is used to make them. Currently, blue LED is used to produce red and green light by exciting phosphor. But dynamic control of colour composition can be achieved by using LEDs of all the three colours; this may happen in the future. In about two decades after blue LED came into being, it has revolutionised white light production. It remains to be seen if any another path-breaking technology can ever displace the LED.
Science Chronicle 