Lattice deformation and phase transition of aluminum nitride studied by density functional theory calculations

The density functional theory (DFT) was employed to understand the ferroelectric behaviors of wurtzite (WZ)-type aluminum nitride (AlN). To explain the decrease in the coercive field (Ec) due to lattice deformation, the total energy and enthalpy of the strained WZ phase were compared to those of the non-polar (NP) phase, which acted as a transition state during polarity switching. The shrinkage of the c-axis length and elongation of the a-axis length were favorable for reducing Ec. In addition, the calculated residual stress in the transient NP phase was as high as 30 GPa, suggesting that such a high residual stress may be related to the polarity switching behavior under a very high electric field.