Akasaki Yong and Blu ray LED big secret

Before the 1993 launch of Nichia blue LED, many technical personnel for gallium nitride (GaN) semiconductor crystal has made great efforts to. Among them, in the history of the development of GaN blue LED can be said to have left an indelible footprint, is a Japanese university professor Akasaki Yong and professor of (Nagoya University) research group.

About 10 years ago, around the village in the litigation case, the author has developed for process validation of blue LED on Tian Ye were interviewed, the interview was based on the re introduce akasaki and Amano achievements.

After 1993, Nichia launched the blue LED, for a period of time the public generally believe that the blue LED is Nichia developed. In this regard, Professor Tian Tian said, the blue LED is the product of many pioneers in order to synthesize gallium nitride (GaN) semiconductor crystal technology and the development of the results of the stick".

The research team of the red sky and the wild, made an important contribution in the development of GaN blue LED. Akasaki won the "Institute of applied physics achievement award" in 2001, there is such a word for: "in the development of GaN type nitride semiconductor materials and devices, akasaki research and the research team is the starting point of all. Through the development of low temperature buffer layer technology, 1986 successfully obtained significantly improved the quality of the crystal, and realized after P type conduction and N type conductivity could not control in 1989, the same year also achieved PN blue light emitting diode. "

Blue LED technology was established in 1985, publicly published in 1986.

In the introduction of the blue LED invention, all of the GaN blue LED mentioned, because the GaN class blue LED is considered to be the prototype of the practical blue LED. In fact, it is necessary to say that the concept of blue hair LED, silicon carbide (SiC) class blue LED as early as the blue LED class before the birth of GaN. However, weak light blue SiC LED output, the development of blue semiconductor lasers aimed at many researchers in blue after LED did not play a role, so now, if not specified, the blue LED refers to GaN blue LED.

The reason why the team has been able to get such a high rating, because they have been insisting on a lot of researchers have to give up the GaN material, efforts to achieve the final blue LED.

The choice of GaN is a difficult road

In order to make blue LED and blue light-emitting diodes such as blue light-emitting diodes, at least need to take the gap in the 2.6eV (V) above the large semiconductor materials. The formula between the luminous wavelength and the band gap energy is

Luminous wavelength (nm) = 1.24/ band gap energy (eV) * 100

Blue light-emitting wavelength of 455 ~ 485nm, in accordance with the formula inverted, the required band gap energy is from 2.55 to 2.72eV. Therefore, in order to achieve blue light-emitting devices, at least more than 2.6eV band gap energy. This kind of semiconductor with a large gap energy is known as a wide band gap semiconductor, according to the formula above, only a wide band gap semiconductor can emit high energy blue region of the short wavelength light.

In the first half of the second half of 1960s to 1980s, the alternate material of the blue light emitting devices SiC, ZnSe (ZnSe) and GaN three. But these three materials are not expected to be the same. According to the difficulty of crystal growth, most researchers have focused on SiC and ZnSe two materials.

And Qi Qi chose GaN. About this choice, published in 2002 he received the award speech Takeda explained.

From about 1970 to the beginning of 80s, dedicated to the study of blue light-emitting devices are mostly based on these three materials (GaN, ZnSe, SiC) as the research object. Only SiC at that time to achieve the PN knot. So a lot of researchers are trying to study the SiC material. The rest chose ZnSe or GaN. The two have in common is not formed P type semiconductor. However, the energy band structure of SiC is an indirect transition type, so it is impossible to achieve strong luminescence, and can not be made into semiconductor lasers. Although ZnSe and GaN are both direct transitions, the PN junction has not yet been realized.

"So, in addition to selecting SiC researchers, most people chose ZnSe. This is because, although ZnSe and GaN are difficult to form crystals, but relatively speaking, ZnSe is easier than GaN.

In addition, ZnSe also has the characteristics of flexible processing. GaN is very difficult to make crystal, and the energy gap larger than ZnSe, so p is considered to be difficult.

"I also know that GaN PN junction and blue light-emitting devices are very difficult to achieve. But since anyway, decided to challenge more difficult GaN. "

Red Qi began to develop blue LED and blue semiconductor lasers have a strong desire to be around 1966. When working at Panasonic Research Institute of Tokyo (later renamed the Matsushita Research Institute) Akasaki (AlN) is mainly engaged in aluminum nitride and gallium arsenide (GaAs) on the growth and properties of crystal, and the use of gallium phosphide (GaAsP) red LED and the gap (GaP) development of green LED. Among them, the red LED, red 1969 successfully developed the external quantum efficiency of the world's highest, up to 2% of the device.

However, the choice of GaN development of blue light-emitting devices is not only red. There are people in the world before he started on the development of GaN blue LED. Muruska in the development of higher brightness red LED in 1969, the American RCA Institute, etc.