a
          \(p\) -type semiconductor is obtained when \(\mathrm{Si}\) or \(Ge\) is doped with a trivalent impurity like aluminium \((Al)\), boron \((B)\), indium \((In)\) etc,

Here, \(n_{i}=1.5 \times 10^{16} \mathrm{m}^{-3}, \quad n_{h}=4.5 \times 10^{22} \mathrm{m}^{-3}\)

As \(\quad n_e, n_{h}=n_{i}^{2}\)

\(n_{e}=\frac{n_{i}^{2}}{n_{h}}=\) \(\frac{\left(1.5 \times 10^{16} \mathrm{m}^{-3}\right)^{2}}{4.5 \times 10^{22} \mathrm{m}^{-3}}\) \(=5 \times 10^{9} \mathrm{m}^{-3}\)