2. Types of semiconductors

Start here

1. Write the abbreviations from the box next to the words and phrases. Which word or phrase is not about semiconductors? Underline it.

Si InP Cu SiGe GaAs Ge GaP InAs SiC GaN InSb C

1. indium phosphide

2. silicon carbide

3. copper

4. gallium nitride

5. indium arsenide

6. gallium phosphide

7. silicon

8. indium antimonide

9. silicon germanium

10. carbon

11. gallium arsenide

12. germanium

Listening

2. Listen to this text and name the types of semiconductors.

Semiconductors are mainly classified into two categories: intrinsic and extrinsic. An intrinsic semiconductor material is chemically very pure and possesses poor conductivity. It has equal numbers of negative carriers (electrons) and positive carriers (holes). Holes and electrons are responsible for current in semiconductor materials. A hole is the absence of an electron in a particular place in an atom. These carriers are produced as a result of thermal agitation of the atoms, even at room temperature. Some bound electrons can acquire sufficient energy to escape from their atoms, becoming free electrons and leaving holes behind. This process of producing hole-electron pairs is called thermal generation.

Whereas an extrinsic semiconductor is an improved intrinsic semiconductor with a small amount of impurities added by a process, known as doping which alters the electrical properties of the semiconductor and improves its conductivity. Introducing impurities into the semiconductor materials (doping process) can control their conductivity. Doping process produces two groups of semiconductors: the negative charge conductor (n-type) and the positive charge conductor (p-type).

Semiconductors are available as either elements or compounds. Silicon and Germanium are the most common elemental semiconductors. Si and Ge both have a crystalline structure called the diamond lattice. That is, each atom has its four nearest neighbors at the corners of a regular tetrahedron with the atom itself being at the center.

In addition to the pure element semiconductors, many alloys and compounds are semiconductors. Compound semiconductors include InSb, InAs, GaP, GaSb, GaAs, SiC, GaN. The advantage of compound semiconductor is that they provide the device engineer with a wide range of energy gaps and mobilities, so that materials are available with properties that meet specific requirements. Some of these semiconductors are therefore called wide band gap semiconductors.

3. Listen again and mark the statements below (T) true or (F) false.

1. There are intrinsic and extrinsic semiconductors.

2. Intrinsic semiconductors have good conductivity.

3. A hole is a positive charge.

4. Doped semiconductors are poor conductors.

5. The process of producing hole-electron pairs is called doping.

6. Introducing impurities into the semiconductor materials is called thermal generation.

7. Semiconductors are available as elements and compounds.