A pure silicon crystal has 5 × 10²⁸ atoms m^-3. It is doped by 2 ppm concentration of pentavalent arsenic. The number of holes are:

Consider n_i = 1.5 × 10¹⁶ m^-3

2.25 × 10⁹ m^-3

2 out of $10^6$ Si atom is doped. Hence total number of electron provided by As is $ N_e = \frac{2\times 5\times 10^{28}}{10^6} = 10^23$

$ N_e N_h = N_i^2 = (1.5\times 10^{16})^2 = 2.25 \times 10^32$

$ N_h = \frac{2.25 \times 10^32}{10^{23}} = 2.25\times 10^9$