| Hiroshi Amano |
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[Slide 6]
[Slide 7]
[Slide 8]
[Slide 9]
[Slide 10]
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[Slide 6]
And, as mentioned by Professor Akasaki, there was the lattice mismatch of 16 % to the sapphire substrate. It was generally thought at the time, that this was a very difficult figure to be overcome in order to get a good crystal.
[Slide 7]
In such a situation, I started the research of the blue light emitting diode. I was a fourth grade student and an utter non-expert, so, naturally, I had many bitter experiences. Firstly, I will talk about the crystal growth apparatus.
[Slide 8]
Far from getting good crystal growth, none of the crystal was obtained. I thought over from various viewpoints why the crystal could not grow. At last, I concluded that I had to observe actual growth situation. This paper reported the observed results.
This represents the growth apparatus. From here the gallium material gas is supplied. And, from here ammonia, the nitrogen material gas, is supplied. These are the main parts of this crystal growth apparatus.
I tried to see inner gas flow using smoke. Then, I saw successfully that the gas flow was avoiding the susceptor, here supporting the sapphire substrate.
From this gas flow observation, I found that the very much higher temperature for gallium nitride growth, than that for conventional semiconductor growth, resulted in a large amount of heat convection, which drove the gas away from the susceptor.
Needless to add, that had to result in no growth. Absolutely no grown film. Then, I changed the gas from hydrogen to nitrogen. In the case of hydrogen gas, the gas flow is very smoothly without turbulence. Changing to nitrogen, the gas flow can be turbulent and flows in the desired way to get the gallium nitride film formation.
[Slide 9]
However, supplying the gas in the turbulent condition initiated many kinds of side reactions, which resulted in this kind of white powder formation. This condition continued without any improvement. So, I made many kinds of alterations to try and overcome this situation and I arrived at last to the formation like this.
[Slide 10]
The gas flow rate had been very slow, such as 5 cm per second, so far. I supplied the gas at a rate 100 times faster than that. For that purpose, I had many troubles to get this part. In this figure, the construction is simplified. I made by myself this part with glass working. There was not much money and no time to order a part as it would take a long time.
I made all the parts by myself. At first, they were failures. After 30 or 40 attempts, I made the glass workings as I wanted them, which resulted in the desirable gas flow.
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