Semiconductors

Question 1

Valence band

Answer 1

The energy band formed in those energy levels of the atoms which contain valence electrons

Question 2

Conduction band

Answer 2

The lowest unfilled energy band formed just above the valence band is called the conduction band

Question 3

Energy gap in solids

Answer 3

The interval between the valence band and the conduction band where no electron states exist

Question 4

How does the energy gap in an intrinsic semiconductor vary when doped with a pentavalent impurity?

Answer 4

Energy gap decreases

Due to the addition of donor atoms, allowable energy levels are introduced at a small distance below the conduction band. These new allowable energy levels are discrete.

Question 5

What are holes?

Answer 5

A hole indicates a vacancy left by an electron.
It is a seat of positive charge of magnitude equal to the charge of an electron.

Question 6

Ratio of number of holes and number of electrons in the conduction band in semiconductors

Answer 6

1

Question 7

Is the ratio of number of holes and number of conduction electrons same, more than 1, less than 1 in
(a) p-type semiconductors
(b) n-type semiconductors

Answer 7

(a) more than 1 (no. of holes > no. of conduction electrons)
(b) less than 1 (no. of holes < no. of conduction electrons)