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

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

TL;DR: band structure basically stays the same since your dopant doesn't increase the electron/hole density enough.

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.

  • \$\begingroup\$ Did you write \$10^{-10}\$ instead of \$10^{10}\$? \$\endgroup\$
    – nidhin
    Oct 6 '19 at 8:42
  • \$\begingroup\$ Yeah my bad.... \$\endgroup\$
    – hatsunearu
    Oct 8 '19 at 18:58

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