Theoretical investigations of physical properties

A computed investigation on the structural, elastic, electronic, phonon frequencies and thermal properties of AlxScyB1-x-yN quaternary alloys in the zinc-blend phase has been made with first-principles methods. The information on the lattice constant, lattice matching to AlN substrate and energy band gaps is indispensable for various practical applications. We have studied the effect of Sc concentration y = 0, 0.152, 0.303, 0.455 and 0.607) on the lattice constant, bulk modulus, elastic constants C-11, C-12 and C-44, band gaps, optical phonon frequencies (omega ro and omega lo), static and high-frequency dielectric coefficient epsilon(0) and epsilon(infinity) and dynamic effective charge Z*. We remark an important deviation from the linear concentration dependence of the lattice constant and bulk modulus. The shear moduli, Young's modulus, Poisson's ratio were estimated in the frame work of the Voigt-Reuss-Hill approximation. The resistance to changes in bond length and lateral expansion in AlxScyB(1-x-y)N increase with increasingy concentration. We observe that at y concentration about 0.11, the F-X indirect fundamental gap becomes F-F direct fundamental gap in AlxScyB1-x-yN. There is well agreement between our results and the experiment data for AlN binary compound which is a support for those of the quaternary alloys that we report for the first time. (C) 2011 Elsevier B.V. All rights reserved.