# What happens if doping concentration is less than Intrinsic concentration? Will the semiconductor act as intrinsic or extrinsic? Please Explain

Si has intrinsic conc of 1.08*10^10 If it is doped with conc less than intrinsic concentration what happens

• I'm guessing, much the same sort of things that happen at pressures less than perfect vacuum or temperatures below 0K. Sep 28 '19 at 14:06

Let's take an example: let's say $$\n_i = 10^{-10}\$$ and you have initially an intrinsic semiconductor. Then $$\n_e = n_i = 10^{-10}\$$.
Let's say you dope N-type with density $$\N_d = 10^{-11}\$$. Assuming full ionization of the dopant, you get $$\n_e = n_i + N_d\$$ (approximately, I believe there's an equation for this).
This means that you have $$\n_e = 1.1 \times 10^{-10} \$$ and $$\n_h = n_i^2 / n_e = 0.909 \times 10^{-10} \$$.
Basically the concentrations don't change enough to matter. This is why when you dope you dope much much greater than $$\n_i\$$ since if you don't dope enough nothing really happens.
• Did you write $10^{-10}$ instead of $10^{10}$? Oct 6 '19 at 8:42