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.

If any doubts please comment.Thanks for your time.

  • $\begingroup$ 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$^{3}$. $\endgroup$ – Jon Custer Apr 9 '17 at 17:03

Atomic density represents number of atoms present per unit volume where as intrinsic carrier density represents number of atoms capable of breaking their bonds(and thus giving rise to free electrons in conduction band) at a specific temperature per unit volume

All the atoms do not break bonds at a specific temperature(under thermal equilibrium) those atoms which are capable of breaking their bonds contribute to intrinsic carrier concentration so intrinsic carrier concentration <= Atomic density

  • $\begingroup$ PAVAN, All CAPS is bad formating, and often interpreted as yelling. Please avoid using this style. $\endgroup$ – stafusa Oct 8 '17 at 20:35

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