Question

Mobility of electrons in $N$ -type $Ge$ is $5000 \,cm ^{2}$ / volt sec and conductivity $5 mho / cm$. If effect of holes is negligible then impurity concentration will be

• A. $6.25 \times 10^{15} / cm ^{3}$
• B. $9.25 \times 10^{14} / cm ^{3}$
• C. $6 \times 10^{13} / cm ^{3}$
• D. $9 \times 10^{13} / cm ^{3}$

Answer 1

Answer: (A)

$\sigma=en_{ e } \mu_{ e } $
$ \Rightarrow n_{e}=\frac{\sigma}{e \mu_{e}}$
$=\frac{5}{1.6 \times 10^{-19} \times 5000}$
$=6.25 \times 10^{15} / cm ^{3}$