Question

A semiconductor has an electron concentration of $8 \times 10^{13}$ per $cm ^{3}$ and a hole concentration of $5 \times 10^{12}$ per $cm ^{3}$. The electron mobility is $25000\, cm ^{2} V ^{-1} s ^{-1}$ and the hole mobility is $100\, cm ^{2} V ^{-1} s ^{-1}$. Then,

• A. the semiconductor is $n$-type
• B. the conductivity is $320\, m \,mho \,cm ^{-1}$
• C. Both (a) and (b)
• D. None of the above

Answer 1

Answer: (C)

$n_{e}=8 \times 10^{13} / cm ^{3}$,
$n_{n}=5 \times 10^{12} / cm ^{3}$
$\mu_{e}=25000\, cm ^{2} V ^{-1} s ^{-1}$
$\mu_{n}=100\, cm ^{2} V ^{-1} s ^{-1}$
$\sigma=n_{e} \mu_{e} e+n_{n} \mu_{n} e$
$=\left(8 \times 10^{13} \times 25000+5 \times 10^{12} \times 100\right) \times 1.6 \times 10^{-19}$
$=320 \times 10^{-3} mho / cm$
$n_{e}>n_{n}$ (n-type)