A pure Si crystal has $5 imes 10^{22}$ atoms $\mathrm{m}^{-3}$. It is doped by 1 ppm concentration

Question

A pure Si crystal has $5 	imes 10^{22}$ atoms $\mathrm{m}^{-3}$. It is doped by 1 ppm concentration of pentavalent impurity. The number of holes is ( $n_i^2=n_h n_e$ )\ (Take $n_i=1.5 	imes 10^{16} \mathrm{~m}^{-3}$ )

Professor PC Thomas Classes · Answer

(a): The electron and holes concentration in a semiconductor in thermal equilibrium is\ $ n_e n_h=n_i^2 	ext { or } n_h=\frac{n_i^2}{n_e} $ \Here, $n_i=1.5 	imes 10^{16} \mathrm{~m}^{-3}, n_e=5 	imes 10^{22} \mathrm{~m}^{-3}$ $ \  	herefore \quad n_h=\frac{\left(1.5 	imes 10^{16}ight)^2}{\left(5 	imes 10^{22}ight)}=\frac{2.25 	imes 10^{32}}{5 	imes 10^{22}}=4.5 	imes 10^9 \mathrm{~m}^{-3} $