First-principles calculations of elastic and optical properties of Aluminum Nitride (AlN) in cubic and hexagonal phase

Abstract

Investigation of elastic and optical properties of AlN in rocksalt, zincblende and wurtzite phase is done under the framework of Density Functional Theory (DFT) with modified Becke Johnson Generalised Gradient Approximation (mBJ-GGA) as exchange-correlation functional. Elastic properties conclude the bonding nature of the AlN in the rocksalt phase as covalent and stiff, while the bonding nature in the zincblende and wurtzite phase is found to be ionic and less stiff as compare to rocksalt phase. The ratio of bulk modulus to shear modulus indicates brittle in all the three phases. The calculated Debye temperature in all the three phases is in good agreement with the available theoretical and experimental works. The optical property shows the AlN is transparent in low energy range and metallic behaviour in the energy range 7.5eV to 10 eV. At the same time, the compound loses its transparency at the high energy range. Our calculated value of the refractive index of AlN in the rocksalt, zincblende and wurtzite phases are in good agreement with the available experimental and theoretical works.