# What is the difference between atomic density and intrinsic concentration?

If a Si sample is doped with boron impurities in the ratio of 1:10^6, it means that for every 10^6 Si atoms, 1 boron atom is added.

I have been given information that atomic density of Si is 5*10^22 atoms/cm^3.

Also intrinsic concentration is 1.5*10^10 atoms/cm^3

To find out the total concentration of boron impurity, have to use the ratio like this

1:10^6 = boron concentration : atomic density of Si.

The question is that why cant intrinsic concentration be used in place of atomic density of Si.Thought that both denotes the Si atom concentrations.

• The 'intrinsic concentration' is the density of electrons (and holes) in an undoped Si sample. Note that it is much much much less than the hole concentration obtained by doping with $10^{16}$B/cm$^{3}$. – Jon Custer Apr 9 '17 at 17:03