Question

For a pure $Si$ crystal has $5 \times 10^{28}$ atom $m ^{-3}$ It is doped by $1 \,PPM$ concentration of pentavalent As. Calculate the number of electron $\&$ holes. Given that $n _{i}=1.5 \times 10^{16} m ^{-3}$ )

• A. $5.4 \times 10^{9} m ^{-3}$
• B. $4.5 \times 10^{9} m ^{-3}$
• C. $4.5 \times 10^{-9} m ^{-3}$
• D. $5.4 \times 10^{-9} m ^{-3}$

Answer 1

Answer: (B)

Each As atom will provide $1$ free electron total no. of free electrons
$n_{e}=\frac{1}{10^{6}} \times 5 \times 10^{28}=5 \times 10^{22} $
$n_{e} n_{h}=n_{i}^{2}$
$\Rightarrow n _{h}=\frac{n_{i}^{2}}{n_{e}}$