Question

A pure silicon crystal has 6 × 10²⁸ atoms. It is doped by 1 PPM concentration of antimony. Calculate the number of holes. Given, nᵢ = 1.2 × 10¹⁶ / m³.

Answer 1

1 atom of Si doped out of 10

6

atoms (1 ppm of As)

⇒ In 5×10

28

atoms net doped =

10

6

5×10

28

=5×10

22

atoms

1 As atom creates 1e

⊝

excen

so, no. of excen electron =5×10

22

=n

e

also, n

e

n

n

=n

1

2

⇒n

n

=

n

e

n

1

2

=

5×10

22

(1.5×10

16

)

2

=4.5×10

9

∴ No. of holes formed =4.5×10

9

.

as n

e

>n

n

→ It is a N - type semiconductor formed.