Question

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

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

Answer 1

Answer: (C)

$n_e=8\times 10^{13}/c{m}^3$,
$n_n=5\times 10^{12}/c{m}^3$
${\mu }_e=25000c{m}^2{V}^{-1}{s}^{-1}$
${\mu }_n=100c{m}^2{V}^{-1}{s}^{-1}$
$\sigma =n_e{\mu }_{e}e+n_n{\mu }_{n}e$
$=\left(8\times 10^{13}\times 25000+5\times 10^{12}\times 100\right)\times 1.6\times 10^{-19}$
$=320\times 10^{-3}mho/cm$
$n_e>n_n$ (n-type)