Polarization, piezoelectric constants and elastic constants of ZnO, MgO   and CdO
  We report first principles density functional calculations of the spontaneous polarizations, piezoelectric constants and elastic constants for the II-VI wurtzite structure ZnO, MgO and CdO. Using our self interaction corrected implementation of density functional theory we obtain polarization values of we obtain polarization values of -0.05, -0.17 and -0.10 C/m$^2$, and piezoelectric constants, $e_{33}$ ($e_{31}$) of 1.34 (-0.57), 2.26 (-0.38) and 1.67 (-0.48) C/m$^2$ for structurally relaxed ZnO, MgO and CdO respectively. These properties are consistently larger in magnitude than the corresponding GaN, AlN and InN analogues. Therefore we predict that larger internal fields will be attainable in ZnO-based polarization field effect transistors than in equivalent GaN-based devices. 
Priya Gopal and Nicola Spaldin