Silicon

Silicon is a very common element. In its pure form silicon is a dark, hard, rather glassy-looking material. The sand, for example, is mostly silicon oxide, i. e. the sand is a compound of silicon and oxygen.

The silicon oxide is an insulator, and when it is necessary we can make a very thin insulation on a piece of silicon by means of controllable oxidation.

Silicon is a semiconductor. If an electric field is set up in the crystal of silicon, the electrons tend to move in the direction of the field and the holes tend to move in the opposite direction. Thus conduction of current in a pure silicon known as intrinsic conduction takes place. If a little impurity is added to silicon, it will become an impurity semiconductor. The addition of impurities is a very efficient way of causing extrinsic conductivity. It appears in addition to intrinsic conductivity.

Elements of group III or group V of the Periodic Table are usually employed as impurities. These elements have either 3 or 5 valence electrons.

14. Read the text again and select the best completion for each sentence. Complete the following sentences using the multiple choice suggested. There might be more than one variant.

1. Silicon is …

a) an unknown element d) a very common element

b) a semiconductor e) an impurity semiconductor

c) a conductor

2. In its pure form silicon is …

a) light-coloured d) glassy-looking

b) hard e) dark

c) soft

3. We can make a very thin insulation on a piece of silicon by means of …

a) an electric field c) controllable oxidation

b) adding impurities d) placing it into another environment

4. Elements which are usually employed as impurities have either…