In 1962, Holonyak and Bevacqua, who worked at GE in New York, USA, took the lead in producing visible light LEDs, which were red light LEDs based on I-V group materials (the recombination of the atoms of the vessel group and the group V in the periodic table). The band gap of the semiconductor material involved in the visible light LED is 1.8-3.1eV, which is converted into a wavelength of 0.4-0.7 μm.
In the 1960s, commercial LEDs have been manufactured, all of which are based on GaAsP (gallium arsenide phosphorous) materials, which can generate red light with a wavelength of 655nm and a luminous intensity of 1 at a current of 20mA. -10mcd, which was mainly used for indicators at the time. Following GaAsP, red LEDs based on GaP (gallium phosphide) have been developed, which have higher efficiency in comparison, but have not made a breakthrough in the application range.
In the 1970s, LEDs of other colors came into being, such as green light based on GaP, orange light and yellow light based on GaAsP.
In the 1980s, with the deepening of research, ED based on GaAlAs (gallium aluminum arsenide) was developed, which has higher efficiency and lower driving voltage. At the same time, research in the field of laser diodes has led to a good development of InGa AIP (steel nickel aluminum phosphorus), resulting in the manufacture of red, yellow, orange and green LEDs based on InGa AIP, They have better light efficiency and longer lifespan.
In the 1990s, high-brightness blue LEDs were developed, which can be fabricated with GaN (gallium nitride), SiC (silicon carbide), and ZnSe (zinc selenide) because of their wide band gaps. Since SiC is an indirect band gap, it is not a good material for blue LEDs, and ZnSe blue LEDs cannot be commercialized due to its short lifespan. The research on LEDs based on GaN materials began in the 1970s. With the deepening of the research, in the 1990s, Nakamura Shuji and his team in Japan successfully developed blue LEDs using advanced material preparation technology. In 1993, Nichia launched the The world’s first blue LED, thus realizing the three primary colors of RGB (red, green, and blue) necessary in the field of color display. But the real technological revolution is using the principle of color synthesis or coating blue LED chips with yttrium aluminum garnet (YAG) phosphors to produce white light.
As mentioned earlier, the vast majority of LEDs are fabricated using Group 1-V compound semiconductors. In fact, LEDs can also be prepared with Group IV materials (such as Si, C-based SiC materials) or 11-V group compounds (such as ZeSe). However, defects are more prone to occur in these materials, resulting in shorter lifetimes. In contrast, LEDs based on AIXGa1-x-yInxN mixed crystal materials have a direct band gap and high material stability.
The life of the LED refers to the working time when the LED brightness decreases by 30%. Under the rated operating conditions, the lifespan of today’s LEDs is between 5,000 and -100,000, compared to 1,000h for incandescent lamps and 10,000h for fluorescent lamps. In fact, the life of an LED depends more on its materials (such as InGaN, InGaAIP, GaAlAs) and the environment used, especially humidity and temperature, so its package is required to have good heat dissipation performance