2 Marks Question & Answers

Part - A '2' Marks Q & A

ANNA UNIVERSITY Q&A

1. What are elemental semiconductors? Give some important elemental semiconductors.

Elemental semiconductors are made from single element of the fourth group elements of the periodic table.

Example

Germanium and silicon.

2. What are the properties of semiconductors?

• They are formed by covalent bond.

• They have empty conduction band.

• They have almost filled valence band.

• These materials have comparatively narrow energy gap.

3. What are compound semiconductors? Give some important compound semiconductors.

Semiconductors which are formed by combining third and fifth group elements or second and sixth group elements in the periodic table are called compound semiconductors.

4. Mention any four advantages of semiconducting materials.

• It behaves as insulator at 0 K and as conductor at high temperatures.

• It has some properties of both conductor and insulator. 

• On doping, n and p-type semiconductors are produced with charge carriers of electrons and holes respectively.

• It has many applications in electronic field such as manufacturing of diodes, transistors, LED's, IC etc.

5. What are the differences between elemental semiconductors and compound semiconductors?

6. Write an expression for the concentration of electrons in the conduction band of an intrinsic semiconductor.

The concentration of electrons in the conduction band of an intrinsic semiconductor is given by

where me* → effective mass of electron

EF → Fermi energy level

EC → Energy corresponds to the bottom of conduction band

T → Absolute temperature

7. Write an expression for the concentration of holes in the valence band of an intrinsic semiconductor.

The concentration of holes in the valence band is given by

mh* → effective mass of hole

T → absolute temperature

EF → Fermi energy

Ev → Energy corresponds to the top of valence band

8. Write an expression for carrier concentration in n-type semiconductor.

9. Write an expression for carrier concentration of holes in the valence band of p-type semiconductor.

The carrier concentration in p-type is given by

10. Define Hall-effect and Hall voltage.

When a conductor carrying a current (I) is placed in a transverse magnetic field (B), a potential difference is produced inside the conductor in a direction normal to the directions of the current and magnetic field.

This phenomenon is known as Hall-effect and the generated voltage is called Hall-voltage.

11. Mention the uses of Hall effect.

• It is used to find type of semiconductor. 

• It is used to measure carrier concentration.

• It is used to find mobility of charge carrier.

• It is used to measure the magnetic flux density using a semiconductor sample of known Hall coefficient.

12. What are the differences between intrinsic and extrinsic semiconductor?

13. What are the differences between n-type and p-type semiconductor?