Intrinsic carrier concentration (ni): definition

Beginner

How many electrons heat alone knocks free in perfectly pure silicon. It is very few.

Novice

The density of electrons (equal to the density of holes) in undoped silicon, about $10^{10}$ per cm³ at room temperature. For comparison there are $5 \times 10^{22}$ silicon atoms per cm³.

Expert

$n_{\mathrm{i}} = \sqrt{N_{\mathrm{c}} N_{\mathrm{v}}}\, e^{-E_{\mathrm{g}}/2kT}$ ; about $9.65 \times 10^9\,\mathrm{cm^{-3}}$ at 300 K by the modern measurement. It rises steeply with temperature, and so do junction leakage ( $\propto n_{\mathrm{i}}^2$ ) and the drift of $V_{\mathrm{T}}$ .