Semiconductor crystals space perfection

                            

          

First experiments to obtain materials in space began 50 years ago. Over the years, the basic techniques and approaches to these investigations have not changed dramatically, but the objectives of the work lying in this line, are quite different: from the search for new heat-resistant metals, scientists have moved to the semiconductor crystals for solar power. For the next experiment in the series prepared by researchers from Institute of Semiconductor Physics. Rzhanov SB RAS together with colleagues from the University of Houston (University of Houston) Aboard the International Space Station (ISS), they want to grow crystals of perfect structure for solar panels.

 

Semiconductor crystals — is the foundation of all electronics, and of course, there are many methods of their production in terrestrial conditions. Unfortunately, they all have common drawbacks: the crystals are often patchy, too small or corrupted by foreign matter. The reasons for that are many, but among them there is one of the most general nature — the force of gravity. In terrestrial conditions, gravity gives rise to the phenomenon of natural convection, mixing a liquid under the influence of a temperature difference in the gravitational field. Under the conditions of weightlessness of space this factor significantly decreases, and it becomes possible to obtain semiconductor Crystals cleaner structure and perfect composition.

The first experiments on the cultivation of materials in space began shortly after the flight Gagarin, in 1961, and the results have often been contradictory. Thus, the crystals Ge (Ca) and InSb (Te), obtained in the experiments of American "Skylab", were highly homogeneous structure, and crystals from the board, "Apollo-Soyuz", by contrast, lost their earthly counterparts. The reasons for such failures are multiple drives: vibration mechanisms, residual microaccelerations (acceleration due to gravity on board the spacecraft is not strictly equal to zero, contrary to misconceptions propagated), some convection effects imperceptible when Earth’s gravity. So the scientists realized that the space environment is much more complicated than it looks at first sight, and many of the experiments were accompanied by numerical simulations. They confirmed that the crystals get a perfect structure in space is possible, but extremely difficult.

Therefore, the next step in exploring possibilities for a perfect crystals become the method of physical modeling. Semiconductor crystals often is produced by directional solidification. Roughly speaking, the crucible with a heated melt of the desired composition is gradually introduced to a lower temperature where the crystals begin to grow. To weaken the terrestrial phenomena thermogravitation in similar conditions, scientists have proposed move is not itself melt and create a moving temperature field with a small radial temperature gradients. This approach allowed us to model space conditions crystal growth experiments and to plan ahead, saving time and material. One of the most striking of these experiments was carried out by the authors of a review article. Semiconductor crystals GaSb (Te) were recrystallized under terrestrial conditions on board AKA "Foton-M3." In both cases, we get a homogeneous crystals of high purity, in which there were some periodic dependence of the physical properties of the structure. In this period, according to the space samples was 90 minutes (which coincides with the period of the satellite), and for the ground — 5-20 minutes.

The next experiment to obtain semiconductor crystals in space is planned in 2013. On board the ISS researchers want to grow crystals of perfect structure for solar panels — already spent finding new methods of practical application. The results of these somewhat exotic experiments help to improve and terrestrial technologies.

Detailed results of theoretical and experimental work on the cultivation of semiconductor crystals in space are described in a review article of the Russian physicists FTI. AF Ioffe RAS and SIC "Space Materials". Publication posted the magazine "Solid State Physics". The materials for the review were the results of the numerous studies of the authors and the brightest of their foreign colleagues.

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