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 $n_i=1.4\times {10}^{10}$ ${\mathrm{c}\mathrm{m}}^{-3}$ )