Question

A semiconductor has equal electron and hole concentration of 3 × 10⁸ m⁻³. On doping with a certain impurity, the hole concentration increases to 6 × 10¹⁰ m⁻³.

1. What type of semiconductor is obtained on doping?
2. Calculate the new electron concentration of the semiconductor.
3. How does the energy gap of semiconductor change with doping? Draw the energy band diagram for it.

Answer 1

Given: Initial intrinsic concentration:

n_i = p_i

= 3 × 10⁸ m⁻³

After doping:

p = 6 × 10¹⁰ m⁻³

a. Since hole concentration increases significantly:

p ≫ n

This indicates acceptor impurity doping.

This is a p-type semiconductor.

b. By using mass action law:

np = `n_i^2`

n = `n_i^2/p`

= `((3 xx 10^8)^2)/(6 xx 10^10)`

= `(9 xx 10^16)/(6 xx 10^10)`

= 1.5 × 10⁶ m⁻³

c.