There is a divided type of substances that is named semiconductors. People got known about these materials in the end of the 19th century, but just in the 20th century scientists managed to obtain more knowledge about them. The first successful research was performed by the Russian scientists in 1923. They proved that semiconductors can be utilized to generate fluctuations. There was no possibility to develop some sophisticated devices as diodes. Only in the beginning of the 50's with the appearing of transistors in 1949 the wide usage of crystal detectors began. That was the start of the era of semiconductor technologies.

The interest to optical features of semiconductors revived due to discovery of simulated emission in semiconductors. It caused the creation of semiconductor laser system based on utilizing of p - n barriers and then on heterojunction.

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