Part A - 2 Marks Questions and Answer

Part - A '2' Marks Q & A

ANNA UNIVERSITY Q&A

1. What are elemental semiconductors? Give some important elemental semiconductors. (A.U Dec 2014)

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? (A.U. June 2013)

• 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. (A.U April 2015)

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.  (April 2013, April 2014)

• 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 Physics for Electrical Engineering are the differences between elemental (A.U June 2012, April 2014, Dec 2015)

6. Write an expression for the concentration of electrons in the conduction band of an intrinsic semiconductor. (A.U. Jan 2014)

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

where m_e → effective mass of electron

E_F → Fermi energy level

E_c → 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.

(A.U. May 2015)

The concentration of holes in the valence band is given by

m_h → effective mass of hole

T → absolute temperature.

E_F → Fermi energy

E_v → Energy corresponds to the top of valence band

8. Write an expression for carrier concentration in n-type semiconductor. (A.U. May 2015)

The carrier concentration in n-type semiconductor is given by

where

ΔE → E_C – E_d Ionisation energy of the donor

N_d → Number of donor atoms per unit volume of the material.

m_e → Effective mass of an electron.

T → Absolute temperature

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

(A.U. Jan 2014)

The carrier concentration in p-type is given by

where

ΔE = (E_v - E_ɑ) ionisation energy of acceptor level

m_h → Effective mass of hole

N_ɑ → Number of acceptor atoms per unit volume of the material.

T → Absolute temperature.

10. Define Hall-effect and Hall voltage.  (A.U. May 2015, Dec 2016)

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. (A.U. May 2013, June 2014)

• 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? (A.U 2008, June 2009, 2012)

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