Some semiconducting materials

It was the Physico-Technical Institute in St. Petersburg that first began investigating solid solutions of semiconducting compounds such as metal sulphides, selenides and tellurides. The object of the research was to obtain new semiconducting materials for the industry.

The investigations are known to have yielded interesting results. A synthesis of these compounds gave a final product which turned out to be an amorphous material. Its physico-chemical properties were similar to those of glass. This glass was found to differ from the conventional oxide glass only in colour.

The alloys of crystalline oxides of certain metals form a wide range of glasses. If alloys of metal oxides form glasses, it would be natural to expect that their chemical analogues, namely sulphides, selenides and tellurides should also form glasses. Therefore, the new inter­esting result obtained was by no means surprising or acci­dental. On the contrary it was the logical outcome of the effort.

To distinguish this group of glasses from the conventional oxide glasses we shall call them chalcogenous glasses. It has to be noted that there is no gap between oxide and chalcogenous glasses.

It was Mendeleyev who first defined glass as a supercooled liquid. This definition has been widely confirmed. It has been shown that by creating a set of required conditions for cooling a melt it is possible to obtain in glassy form many substances surrounding us.

Until recently glass as a material for practical use was represented only in the form of oxide glasses. Today we can speak of the advent of another class of glasses – of a new material for a wide range of uses. What are the properties of those glasses?

If we considered the properties of chalcogenous glasses we could see that they could be distinguished for their transparency, the region of this transparency covering a range from 0,7 to at least 25 micrones. When compared with the oxide glasses they have a far lower softening point. They do not react to moisture, acids or organic solvents. They are soluble in alkalies. They are distinguished for their stability.

It would be interesting to state that they can be classed with typical semiconductors. Their conductivity turned out to reach the conductivity which is 1,000 times higher than that of such classical semiconductor as crystalline selenium.

Having carried out a series of experiments the scientists learned that the conduction of glass was of a purely electronic character that is why this new class of substances might be called "vitreous semiconductors". A very important feature of these semiconductors is high radiation resistance. The conductivity of vitreous semiconductors is hardly affected by any form of radiation.

Vitreous semiconductors were applied in electronics for their photoelectric properties. They were first used in TV tubes. Thanks to their radiation resistance tubes working on vitreous semiconductors are the only ones that are suitable for operation in outer space. Vitreous semiconductors are now being used for the development of a technique for obtaining a photographic image without the use of chemicals. Many Institutes and scientists are conducting thorough investigations on vitreous semiconductors.

8. Answer the questions to the text:

1. What was the object of St. Petersburg investigators’ research? 2. What was the final product? 3. What do the alloys of crystalline oxides of certain metals form? 4. What types of glasses do you know? 5. What glasses are called chalcegenous? 6. What are the properties of chalcogenous glasses? 7. What is the difference between oxide and chalcogenous glasses? 8. What is the conduction of glass? 10. What class of substances can we call "vitreous” semiconductors? 11. What are the properties of vitreous semiconductors?

9. Find the pairs of antonyms and remember them:

hard, solid, wide, liquid, cool, low, narrow, heat, big, small, suitable, soft, high, unsuitable.

10. Find the pairs of synonyms and remember them:

thanks to, to get, to require, finally, to obtain, usual, due to, to demand, at last, ordinary.

11. Translate the words in the brackets into English:

1. A synthesis of these compounds gave а (окончательный) product which turned to be an amorphous material. 2. (Цель) of this research was to obtain new semiconducting materials for the industry. 3. (Чтобы отличить) this group of glasses from the conventional oxide glasses we shall call them chalco­genous glasses. 4. (Наконец) it has been shown that it is possible to obtain in glassyjorm many substances surrounding us. 5. However, (как правило) these glasses are obtained in very small quantities. 6. When compared with the oxide glasses these glasses have (гораздо более низкую) softening point. 7. (Благодаря) to their radiation resistance tubes work­ing on vitreous semiconductors are suitable for operation in outer space. 8. The (проводимость) of vitreous semicon­ductors is hardly affected by (любой) form of radiation.

12. Read the text and add the information of the previous text with the following facts: a) the discoverer of vitreous semiconductors; b) the laboratory dealt with chalcogenous glasses; c) applications.

Chalcogenous glasses and vitreous semiconductors have been discovered by the Laboratory of Photoelectric Phenomena of the Physico-Technical Institute. Russian scientist B. Kolomiets was working in the field of solid state physics. For some years he has been working in the field of complex semiconduc­tors. He is known to have discovered a new class of glasses in general and vitreous semiconductors in particular. He is the author of a well-known work "Vitreous Semiconductors".

Vitreous semiconductors were first applied in electronics for their photoelectric properties. In vitreous semiconductors the photoelectric effect manifests itself in a wide range of wave-length.

The telecast conducted from the Vostok-2 piloted by H. Titov was realized with the help of a tube working on vitreous semiconductors. This was also the case with the Soyuz-3 piloted by G. Beregovoy.

TV tubes for transmitting images on the basis of the photoelectric effect had been introduced before the advent of vitreous semiconductors. But the vitreous semiconductors are known to have considerably improved their sensitivity.

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