ABSTRACT
Light-emitting diodes (LEDs) are not new topics. The development history of LEDs has experienced more than 100 years since Henry Joseph Round published the first report on electroluminescence in 1907 [1].The first practical visible solid state LED based on GaAsP on GaAs substrates was invented in 1962 by Nick Holonyak and Bevacqua of the General Electric Company [2]. Then the General Electric (GE) Corporation launched the first commercial GaAsP LED emitting in the visible red wavelength range in the early 1960s. The next several years, from the late 1960s to the mid-1970s, red LED application opened up the emerging market in numeric displays. Driven at first by calculators, then by wristwatches, M. George Craford made the first demonstration of a yellow LED in 1972 [3]. New materials and techniques enabled high-brightness (HB) LEDs covering from yellow to red spectrum. Nevertheless, GaP- and GaAs-based materials are difficult to prepare blue band LEDs because of 464bandgap restriction. There was a lack of blue band in the visible light until the discovery of the GaN-based material. In 1989, Isamu Akasaki and Hiroshi Amano from Nagoya University demonstrated the first true p-type doping and p-type conductivity in GaN. Mg-doping of GaN is the basis for all nitride-based LEDs and laser diodes [4]. In 1992, they reported the first GaN p-n-homojunction LED that emitted light in the ultraviolet (UV) and blue spectral range [5]. While Shuji Nakamura of Nichia Chemical Industries Corporation developed a two-flow organometallic vapor-phase epitaxy (OMVPE) growth system, the first blue InGaN double-heterostructure LEDs were demonstrated with efficiencies up to 10%. Nakamura’s series of inventions had made blue LEDs turn to practical [6–10]. In the development history of blue LEDs, Isamu Akasaki and Hiroshi Amano solved the basic scientific problems in the growth of materials especially in the p-type doping in GaN, and Nakamura’s contribution had pushed the blue LED technologies to the industry. In view of their contribution, the Nobel Prize in Physics 2014 was awarded jointly to Isamu Akasaki, Hiroshi Amano, and Shuji Nakamura for the invention of efficient blue light-emitting diodes which has enabled bright and energy-saving white light sources [11]. A detailed account of their contributions can be referred to the book The Blue Laser Diode written by Nakamura and Fasol (1997) [12].
