Question

The intrinsic number density of charge carriers in a semiconductor is $2.5\times 10^{13}c{m}^{-3}$,It is doped with donor atoms of number density $1.25\times 10^{17}c{m}^{-3}$, the ratio of conductivities of doped and intrinsic semiconductors is

• A. 5000
• B. 3000
• C. 2000
• D. 1000.

Answer 1

Answer: (A)

$n_e=2.5\times 10^{13}/c{m}^3$
$n_d=1.25\times 10^{17}/c{m}^3$
$\frac{{\sigma }_d}{{\sigma }_e}=?$
$\sigma \alpha n_e$
$\sigma =\frac{1}{\rho }=n_e{\mu }_e\cdot e$
$\frac{{\sigma }_d}{{\sigma }_e}=\frac{n_d}{n_e}=\frac{1.25\times 10^{17}}{2.5\times 10^{13}}$
$\frac{{\sigma }_d}{{\sigma }_e}=5000$