There is a detached class of substances which is named quasi-conductors. In the first time that unique type was discovered in the 1890's but more thoroughly it began to be researched just after the First World War in Europe and in Soviet Union. In 1923 Russian physicists proved the ability of utilizing of semiconductor-metal contacts to quicken the producing of fluctuations. During several years igbt modules were ejected by tubes. First transistor was created in Bell's laboratory in 1949. That event impacted on the quick improvement of semiconductor devices. Since then a lot of persons all over the world become interested in such type of substance as semiconductors.

The interest to optical characteristics of semiconductors revived due to research of induced emission in semiconductors. It caused the appearing of semiconductor laser system based on utilizing of p - n barriers and then on heterojunction.

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