The intrinsic conductivity of germanium at 27° is 2.13 mho m^–1 and mobilities of electrons and holes are 0.38 and $0.18 m^2V^{–1}s^{–1}$ respectively. The density of charge carriers is

$2.37 × 10^{19} m^{–3}$

Conductivity, $σ=\frac{1}{ρ}=e(n_eμ_e+n_hμ_h)$ i.e, $2.13=1.6×10^{-19}(0.38+0.18)n_i$

(Since in intrinsic semi-conductor, $n_e = n_h = n_i$)

∴ density of charge carriers, $n_i=\frac{2.13}{1.6×10^{-19}×0.56}=2.37 × 10^{19} m^{–3}$