A Ge specimen is doped with Al. The concentration of acceptor atoms is 10²¹ atoms / m³ . Given that the intrinsic concentration of electron -hole pairs is 10¹⁹ / m³ , the concentration of electrons in the specimen is

When Ge specimen is doped with Al, then concentration of acceptor atoms is also called concentration of holes. Using formula, ${\mathrm{n}}_{\mathrm{i}}^2={\mathrm{n}}_0{\mathrm{p}}_0$
where
n₁ = concentration of electron hole pair = 10¹⁹m^-3
n₀ = concentration of electron
p₀ = concentration of holes = 10²¹atom m^-3
$\Rightarrow {\left({10}^{19}\right)}^2={10}^{21}\times {\mathrm{n}}_0\Rightarrow {\mathrm{n}}_0={10}^{17}{\mathrm{m}}^{-3}$