Question

The intrinsic number density of charge carriers in a semiconductor is $2.5\times10^{13}cm^{-3}$,It is doped with donor atoms of number density $1.25\times10^{17}cm^{-3}$, the ratio of conductivities of doped and intrinsic semiconductors is

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

Answer 1

Answer: (A)

$n_{e}=2.5 \times 10^{13} / cm ^{3}$
$n_{d}=1.25 \times 10^{17} / cm ^{3}$
$\frac{\sigma_{d}}{\sigma_{e}}=?$
$\sigma \alpha \,n_{e}$
$\sigma=\frac{1}{\rho}=n_{e} \mu_{e} \cdot e$
$\frac{\sigma_{d}}{\sigma_{e}}=\frac{n_{d}}{n_{e}}=\frac{1.25 \times 10^{17}}{2.5 \times 10^{13}}$
$\frac{\sigma_{d}}{\sigma_{e}}=5000$