Growing Quantum Dots
Now physicists need not fully control the growth of laser crystals, because the crystals grow themselves. Professor Nikolay Ledentsov and his team at the Ioffe Physico-Technical Institute have learned how to provide special conditions in which crystals can grow defectless.
Growing crystals with enhanced characteristics is possible on the basis of the effect of quantum dots. A quantum dot is a tiny islet of one material lost in the monocrystal of the other material. For a long time the scientists thought that it is impossible to grow a perfect crystal with “raisins” of other material inside. However, researchers at the laboratory of Zhores Alferov have proved that the grown crystals are good for lasers.
Technology of growing is very important. Usually heterostructural materials, e.g. consisted of gallium arsenid and indium arsenid, are made by placing a layer by layer. Now the researchers can do without this laborious procedure. According to professor Ledentsov it is enough to choose right conditions: temperature, deposition rates, ratios between atom flows etc. In this case a perfect material will grow and the “raisins” will arrange in a strict order. Having known regularities of the growth, it is possible to make beads, chains, “saucers”, small or big islands of quantum dots etc.
The physicists believe that the lasers on quantum dots will be widely used in industry. For example, plates for most common lasers with a wavelength of 1.3 – 1.55 micron will be grown in this way. Using self-arrangement, the scientists have made a crystal for vertical laser with a wavelength of 1.3 micron, which is a key device for telecommunications. In this laser light goes upwards. The vertical laser works as a LED (light emitting diode) with a perfect spectral quality, narrow directional diagram and high efficiency. A similar vertical laser can be made in ultraviolet range, which is used for optical recording.
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