Strain engineering of ZnO thermal conductivity

Using a combination of equilibrium classical molecular dynamics (within the Green-Kubo formalism) and the Boltzmann transport equation, we study the effect of strain on the ZnO thermal conductivity focusing in particular on the case of hydrostatic and uniaxial strain. The results show that in the case of hydrostatic strain up to +/- 4%, we can obtain thermal conductivity variations of more than 100%, while for uniaxial strains the calculated thermal conductivity variations are comparatively less pronounced. In particular, by imposing uniaxial compressive strains up to -4%, we estimate a corresponding thermal conductivity variation close to zero. The mode analysis based on the solution of the Boltzmann transport equation shows that for hydrostatic strains, the thermal conductivity variations are mainly due to a corresponding modification of the phonon relaxations times. Finally, we provide evidence that for uniaxial compressive strains the contribution of the phonon relaxations time is balanced by the increase of the group velocities leading to a thermal conductivity almost unaffected by strain.