Spontaneous polarization and piezoelectric properties of AlN nanowires: Maximally localized Wannier functions analysis

The spontaneous polarization and piezoelectric properties of AlN nanowires (NWs) are investigated in terms of local dipole obtained by maximally localized Wannier functions. It is found that the value of spontaneous polarization is larger in NWs than in the bulk, and will increase by decreasing the NWs size. A further analysis is performed from the point of view of lattice and surface relaxation occurring in the NWs. We show that surface relaxation enhances the spontaneous polarization, while the change of lattice parameter plays a negative role. For the piezoelectric property, we find that it is slightly improved compared with bulk and is similar in a certain range of NW diameters. These findings are of guiding significance help for the fabrication of piezoelectric devices based on AlN NWs.