| Hiroshi Amano |
 |
|
|
 |
 |
|
[Slide 11]
[Slide 12]
[Slide 13]
[Slide 14]
[Slide 15]
[Slide 16]
[Slide 17]
|
[Slide 11]
This is the paper that summarized these trials. The first key point was to dare to supply the gas for gallium and ammonia together, which was contrary to common sense at that time to avoid their reaction. The second point was that the gas flow rate was set at a very high rate that was far beyond the common sense of MOCVD at that time. Finally, I made this part of the susceptor, which I made also by myself, cut at an angle to realize the desired gas flow.
[Slide 12]
Using these results, I made it possible to supply the gas with a certain level of controllability. As for the growth apparatus, a certain level of stability was accomplished. Using this type of apparatus, I succeeded in growing, for example, this mixed crystal, aluminum gallium nitride, with very high controllability. This mixed crystal had not been controlled by the former method with a very slow gas rate.
[Slide 13]
Now I will proceed to the growth techniques.
[Slide 14]
I had been working everyday in university laboratory, continuing the growth experiments. Not a day I had been absent. Counting up the times of the experiments, I had done over 1,500 experiments. But the obtained crystals were always like frosted glass. I had been working body and soul on these experiments. But, in vain. During this period, other master-course students found places of employment one by one. They got jobs lined up, but I had no hope to get a job and necessarily decided to remain as a doctor-course student. The results of the experiments didn't come to much, and so, I could not prepare the scenario for the master's thesis at all. It was a miserable situation for me.
[Slide 15]
One day, it just happened that the crystal growth apparatus was out of order and the growth temperature could not be raised to the desired one. One idea popped into my mind and I tried to pre-deposit an AlN thin film before the growth of gallium nitride, as Professor Akasaki has talked about. During that process, the condition of the apparatus began to improve, so I raised the temperature and grew gallium nitride. When I took out the specimen sapphire, the sapphire surface looked just the same as before. I wondered if I had forgotten to flow the material gases.
When I got out of the clean room and checked the surface by the microscope, I definitely had film growth. I cannot forget even nowc how can I describe itc the excitement which made my heart race.
As talked now, I understood that this technique had enabled me to fabricate a superior crystal with good reproducibility. So, I next started to contend with the problem of conductivity control.
[Slide 16]
At that time, according to some people, the crystal of p-type gallium nitride was said to be unrealizable. The trigger to overcome that difficulty also happened by accident.
[Slide 17]
Under the internship program in my doctor-course curriculum, I was studying thanks to Musashino Telecommunication Laboratory (NTT). My work was on crystal evaluation by the cathode luminescence method. The apparatus was this. During the experiments for that study, I experienced a very curious phenomenon.
|
|
|
