Question

Pure $Si$ at $500K$ has equal number of electron $\left(n_e\right)$ and hole $\left(n_h\right)$ concentration of $1.5\times {10}^{16}{m}^{-3}$. Doping by indium increases $n_h$ to $4.5\times {10}^{22}{m}^{-3}$. The doped semiconductor is of

• A. $n$-type with electron concentration $n_e=5\times {10}^{22}{m}^{-3}$
• B. $p$-type with electron concentration $n_e=2.5\times {10}^{10}{m}^{-3}$
• C. $n$-type with electron concentration $n_e=2.5\times {10}^{23}{m}^{-3}$
• D. $p$-type having electron concentrations $n_e=5\times {10}^9{m}^{-3}$

Answer 1

Answer: (D)

$p$-type having electron concentrations $n_e=5\times {10}^9{m}^{-3}$

$n_i^2=n_e{n}_h$
${(1.5\times {10}^{16})}^2=n_e(4.5\times {10}^{22})$
$n_e=0.5\times {10}^{10}$
$n_e=5\times {10}^9$
$n_h=4.5\times {10}^{22}$
$n_h\gg n_e$
Semiconductor is $p$-type and $n_e=5\times {10}^9{m}^{-3}$.