Zinc-blende AIN and GaN under pressure: structural, electronic, elastic and piezoelectric properties

In this paper we report a theoretical study of the structural, elastic, electronic and piezoelectric properties of zinc-blende AlN and GaN under the pressure effect. The study is focused on the first-principles all electron full-potential augmented plane wave plus local orbitals calculations within the density-functional theory. The results of bulk properties, including lattice constants, bulk modulus and derivatives and band structures are obtained and compared using both the local density approximation (LDA) and the generalized gradient approximation (GGA) for the exchange-correlation functional. We find that the GGA does not give a significant improvement over LDA. We also report calculations for elastic constants as well as the internal-strained parameter and their behaviour under pressure. The electronic energy levels and ionicity factor are studied under hydrostatic pressure. We extend our investigation to the study of the stress effect on piezoelectric constants and transverse effective charges. Our results show that III-V nitrides resemble II-VI compounds in terms of the sign of the piezoelectric constants. The piezoelectric constants and transverse effective charges vary nonlinearly with pressure.