A $\mathrm{p}-\mathrm{n}$ junction has acceptor impurity concentration of ${10}^{17} {\mathrm{c}\mathrm{m}}^{-3}$ in the $\mathrm{p}$ side and donor impurity concentration of ${10}^{16}$ ${\mathrm{c}\mathrm{m}}^{-3}$ in the $\mathrm{n}$ side. The contact potential at the junction is ($kT=$ thermal energy, intrinsic carrier concentration $n_i=1.4\times {10}^{10}$ ${\mathrm{c}\mathrm{m}}^{-3}$ )

• Correct answer
  A

  $\left(\frac{kT}{e}\right)$ ln (${4\times 10}^{12}$)
• B

  $\left(\frac{kT}{e}\right)$ ln (${2.5\times 10}^{23}$)
• C

  $\left(\frac{kT}{e}\right)$ ln (${10}^{23}$)
• D

  $\left(\frac{kT}{e}\right)$ ln (${10}^9$)

Hence, the correct answer is option: 'A'.