Part III Reading Comprehension
Semiconducting Materials
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. Semiconductor materials are the foundation of modern electronics, including radio, computers, telephones, and many other devices. Such devices include transistors, solar cells, many kinds of diodes including the light-emitting diode, the silicon controlled rectifier, and digital and analog integrated circuits.
In a metallic conductor, current is carried by the flow of electrons. In semiconductors, current is often schematized as being carried either by the flow of electrons or by the flow of positively charged "holes" in the electron structure of the material. Actually, however, in both cases only electron movements are involved.
Common semiconducting materials are crystalline solids, but amorphous and liquid semiconductors are known. These include hydrogenated amorphous silicon and mixtures of arsenic, selenium and tellurium in a variety of proportions. Such compounds share with better known semiconductors intermediate conductivity and a rapid variation of conductivity with temperature, as well as occasional negative resistance. Such disordered materials lack the rigid crystalline structure of conventional semiconductors such as silicon and are generally used in thin film structures, which are less demanding for as concerns the electronic quality of the material and thus are relatively insensitive to impurities and radiation damage. Organic semiconductors, that is, organic materials with properties resembling conventional semiconductors, are also known.
Silicon is used to create most semiconductors commercially. Dozens of other materials are used, including germanium, gallium arsenide, and silicon carbide. A pure semiconductor is often called an “intrinsic” semiconductor. The electronic properties and the conductivity of a semiconductor can be changed in a controlled manner by adding very small quantities of other elements, called “dopants”, to the intrinsic material. In crystalline silicon typically this is achieved by adding impurities of boron or phosphorus to the melt and then allowing the melt to solidify into the crystal. This process is called "doping".
9. Какое из приведенных предложений соответствует содержанию текста? 5 вопросов по 2 балла.
1. a) Semiconducting materials appeared before the World War II. .
b) Semiconducting materials are used in many electronic devices nowadays.
2. a) Electron movements are involved in metal conductors only.
b) Electron movements are involved in both metal conductors and semiconductors.
3. a) Semiconducting materials are crystalline solids only.
b) Semiconducting materials are solid, amorphous and liquid.
4. a) The electronic properties and the conductivity of a semiconductor can be changed by adding very small quantities of other elements.
b) The electronic properties and the conductivity of a semiconductor cannot be changed.
5. a) Silicon is the only material used for semiconductors.
b) Many materials are used for semiconductors.
Дополните предложения в соответствии с содержанием текста. 5 вопросов по 2 балла.
1. A semiconductor is a) a material b) a device c) a process.
2. Amorphous and liquid semiconductors a) have b) need c) don’t have rigid crystalline structure.
3. In organic semiconductors organic materials have properties which are a) similar b) different c) partially similar to conventional semiconductors.
4. Silicon is used to create a) all b) some c) most semiconductors.
5. A pure semiconductor is called a) intrinsic b) dopant c) organic.
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