Question

Estimate the proportion of boron impurity which will increase the conductivity of a pure silicon sample by a factor of 100. Assume that each boron atom creates a hole and the concentration of holes in pure silicon at the same temperature is 7 x 10¹⁵ holes per cubic metre. Density of silicon is 5 x 10²⁸ atoms per cubic metre.

Answer 1

Total no.of charge carriers initially = 2 x 7 x10¹⁵ = 14 x10¹⁵/Cubic meter

Finally the total no.of charge carriers = 14 x10¹⁷ / m³

We know :

The product of the concentrations of holes and conduction electrons remains, almost the same.

Let x be the no.of holes.

=>1 atom of Boron is added per