249 Chapter 246 Shocking Every Step (5)

The sixth level, the sandwich (meat sandwich?) Blue LED.

————————

Although GaN (Gallium Nitride) is difficult to manufacture, its advantages are also outstanding, that is, its physical and chemical properties are very stable.It has the characteristics of high thermal conductivity, high temperature resistance, radiation resistance, acid and alkali resistance, high strength and high hardness.

Why ZnSe (zinc selenide) did not succeed in the end is also because of the problem of product stability.

As the current key research direction in the LED field, ZnSe is progressing quite quickly.The blue LED made by Shan M using ZnSe has even reached the level of lasers, but it cannot solve the lifespan problem.

Thousands of scientists around the world have almost completely opened up the road of ZnSe.The finish line is right in front of us, and everyone is excited about it.But it is a pity that it is this last short step that has brought together tens of thousands of human science and technology elites and hundreds of millions of dollars in scientific research funding.

This field has not been completely abandoned even in later generations.A search on the Internet can also find pieces of related papers and technical discussions.

————————

But these are not matters of Yongxing.The problem he wants to solve immediately is to increase the brightness of the LED.

Why PN junction blue LED can not be used as the final product, it is because of the product of this structure, its brightness is not enough!

So what kind of structure has enough brightness? This is the sandwich structure.

GaN (gallium nitride) has a wider band gap.I introduced it earlier.When the band gap is wider, the wavelength of the emitted light wave is shorter.

Now there is a new problem, that is, the wavelength of the light wave emitted by the LED using this material is too short!So that it went out of the visible range and went to the ultraviolet region.Human eyes can't see it!

However, this problem is relatively easy to solve.As long as the composition ratio of In is increased, the light wave is adjusted back to the visible range of the human eye, that is, the blue region.

In addition, a double heterojunction structure can achieve higher luminous efficiency.

Double heterojunction is also called "sandwich" structure.That is, in the middle of the PN structure, a semiconductor layer with a larger energy gap than the light-emitting layer is added.In this structure, the carriers will be confined in the middle by the materials on both sides, which has a higher carrier concentration and luminous efficiency.

As for what is the energy gap and what is the carrier, I will not expand here.These nouns are too complicated, they can be 10,000 words, and I can't finish them.

In short, like a sandwich, the meat in the middle is a bit more delicious.

If you don’t know what a sandwich is, it’s called a roux-moon structure, that’s okay!

Based on these two theories, using the InGaNGaN sandwich structure should produce brighter blue LEDs.

————————

Nakamura's starting time for this LED research was probably in the middle of 1992.This time point is rather strange, because since March 1991 to this time, more than a year has passed.

But there is also an explanation, that is, his thinking is based on the research results published by Professor Akasaki in 1992.

Professor Akasaki and his team released a result in 1992. They used p-type AlGaN and n-type AlGaN as interlayers, and Zn and Si co-doped GaN as meat, thus cooking the first edible sandwich. Produced a brighter blue LED than the previous pn junction type.

When the hero Nakamura saw this paper, his thoughts flowed, and with a big wave of his hand, his results were released.

Cheng Yongxing obviously does not need to wait another two years. His goal is to get it in place at one time. At this point, all that is left is the industrialization work.

According to this theory, Cheng Yongxing began to charge towards the ultimate structure of blue LEDs, the sandwich structure.

There is not much to introduce about the production process at this stage.This is a standard process, the only thing required is time and patience.

————————

In the LED group, the division of labor and cooperation among the students is still in progress. Their time is not much, and the actual work intensity is not very high with the addition of several groups taking turns.

But among these people, interesting changes have also taken place.The biggest change is the translocation of subject and object between group members.

It stands to reason that it is Yan Liang and Gu Ming who have more experience in the operation of semiconductor equipment. They should naturally lead the operation of each group.But over time, the girls gradually caught up.

The main reason here is group operations.The girls who specialize in testing are always united and live together. They help each other at work and improve very quickly.

However, Yan Liang, Gu Ming and other people have different majors, and they can't borrow from each other, and they can easily fall into a singles situation.

Among this group of people, Feng Yan, the academic tyrant, finally gradually revealed his edge.

With the cooperation of the girls, she actually took the lead and wrote a paper on red LED optimization.

————————

The work of the group is basically left to their freedom, which is completely different from MEMS.In the MEMS project, everyone has no room to play, and it’s not bad to be able to do it step by step.

And this LED project team does not have any goals or directions. Anyway, everyone can figure it out, and several people will have a division of labor and find work.

Cheng Yongxing has never been engaged in the production of semiconductors, nor does he know what to do.The work of the LED team belongs to finding a needle in a haystack. What can be found is nothing.

In addition, this so-called LED team is also laying the foundation for the next step of production, and everyone is groping forward.

As for future mass production, take one step and count as one step.

————————

The weather is getting cold day by day.Soon, it's the windbreaker season again.

But Cheng Yongxing didn't dare to take out his clothes at all this time.The scene encountered in spring is repeated in autumn.

The name Cheng Yongxing has reached a point where no one knows it on campus and among students.But this fame is not due to his technological achievements, but because of his sadness.

He has contributed two consecutive gossip news to the boring campus life.Especially this time, the sadness contained in it has made countless people sigh.

Many familiar brothers and sisters, when they met Cheng Yongxing, basically didn't speak much, just put their dirty or greasy hands on Cheng Yongxing's shoulders and sighed quietly!

After waiting for the surrounding crowd to be inexplicable, they patted Cheng Yongxing on the shoulder or chest again, patted their hands clean, and then turned and left.

————————

Perhaps because of the arrival of autumn, everything became sad.

Recently, no matter who has something that goes wrong, he always runs to Cheng Yongxing.Pat him on the shoulder, then looked at his solemn expression.After that, their moods can be much better!

When Cheng Yongxing encountered this situation, he couldn't laugh or cry, so he had to observe a moment of silence and then came back to wash his clothes.

Cheng Yongxing pressed the windbreaker bought at the beginning of the year under the box.It seems that I can't buy things from the beautiful salesperson in the future. The price-performance ratio of such delicate clothes is really outrageous.

Due to the admission of freshmen, a new batch of students in military uniforms appeared on campus.In order to avoid being considered freshmen, sophomores will try to avoid wearing military uniforms, with Cheng Yongxing being the exception.