The Electrical Conductivity of Zinc Oxide

The electrical conductivity of zinc oxide for an average sample obeys the following equations, $\ensuremath{\sigma}={10}^{\ensuremath{-}2}\mathrm{exp}(\ensuremath{-}2\ifmmode\times\else\texttimes\fi{}\frac{{10}^{\ensuremath{-}2}}{\mathrm{kT}})$ ${\mathrm{ohm}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for $T<25$\ifmmode^\circ\else\textdegree\fi{}C and $\ensuremath{\sigma}={10}^{2}\mathrm{exp}(\ensuremath{-}7\ifmmode\times\else\texttimes\fi{}\frac{{10}^{\ensuremath{-}1}}{\mathrm{kT}})$ ${\mathrm{ohm}}^{\ensuremath{-}1}$ ${\mathrm{cm}}^{\ensuremath{-}1}$ for ${400}^{\ensuremath{\circ}}\mathrm{C}<T<{700}^{\ensuremath{\circ}}\mathrm{C}$. The conductivity in the lower temperature range is believed to be due to the ionization of interstitial zinc atom pairs, whose ionization energy is 2\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}2}$ volt or less. Conductivity of this type reaches saturation about room temperature. In the higher temperature range the conductivity is caused by the ionization of single interstitial zinc atoms, whose ionization energy is 7\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}1}$ volt. At 800\ifmmode^\circ\else\textdegree\fi{}C the conductivity of this type begins to reach saturation. Hall effect measurements show the free electron density to be about ${10}^{15}$ ${\mathrm{cm}}^{\ensuremath{-}3}$ at room temperature. The fraction of pairs existing is ${10}^{\ensuremath{-}3}$ which is a factor of ten larger than the a priori probability.