There is a detached type of substances which is named semiconductors. This class was discovered in early 1980's but there were no needed technologies to carry on the further researches. The research of semiconductors was continued just in the 1920's. In 1923 Russian scientists proved the ability of usage of semiconductor-metal contacts to quicken the producing of fluctuations. There was no possibility to create some sophisticated devices as semiconductor assembly. The most significant event in the history of semiconductor devices was the creation of the first transistor by Bell corporation in 1949. Since then many persons all over the world become interested in such kind of matter as semiconductors.
The interest to optical characteristics of semiconductors revived because of research of simulated emission in semiconductors. It caused the appearing of semiconductor laser system based on usage of p - n barriers and then on heterojunction.
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