Spontaneous polarization and piezoelectric constants of III-V nitrides

The spontaneous polarization, dynamical Born charges, and piezoelectric of the III-V nitrides AlN, GaN, and InN are studied ab initio using Berry phase approach to polarization in solids. The piezoelectric constants found to be up 10 times larger than in conventional III-V's and II-VI's, comparable to those of ZnO. Further properties at variance with those of III-V compounds are the sign of the piezoelectric constants (positive as in II-VI's) and the very large spontaneous polarization.