Optical and piezoelectric anomalies of ordered (Sc, Ga) N and (Sc, In) N ternaries
Department of Physical Sciences, Jordan University of Science and Technology, Irbid-22110, Jordan
Corresponding author: a firstname.lastname@example.org
Revised: 1 June 2008
Published online: 22 August 2008
Theoretical results are presented regarding the incorporation of Scandium into wurtzite GaN and InN binaries. The electric, optical and piezoelectric properties of the resulting ScGaN and ScInN systems are reported by using first-principles Local-density approximation (LDA) within density functional theory (DFT), Berry phase approach within modern theory of polarization and phonon calculations within the density functional perturbation theory. Our results predict the existence of breaking-symmetry structural phase transition in ordered Sc0.5Ga0.5N and Sc0.5In0.5N alloys when subjected to a compressive or tensile strain. Moreover, our results demonstrate the existence of symmetry preserving pressure-induced isostructural phase transitions in ordered ScGaN and ScInN systems for different Sc concentrations. It has been shown that the existence of isostructural phase transitions leads to dramatic changes in optical, acoustic, and piezoelectric properties of ordered ScGaN and ScInN systems under high pressure. In particular, this study demonstrates that the existence of first-order isostructural phase transitions in Sc1Ga1N2 at a critical hydrostatic pressure of 12.3 GPa leads to a huge enhancement of piezoelectricity (i.e., the e33 piezoelectric coefficient adopts a huge value as large as 13 C/m. In addition, It has been shown that ordered Sc0.5Ga0.5N and Sc0.5In0.5N alloys exhibit tremendous piezoelectric response, associated with a breaking-symmetry phase transition from nonpolar /mcc space group to a polar mc structure, at fixed Ga, In and Sc compositions, as a function of the in-plane compressive and tensile strains. We also reveal the reason behind, and consequences of, these unusual properties associated with the strain-induced and pressure-induced structural phase transitions in the novel ScGaN and ScInN ordered structures.
PACS: 71.15.-m – Methods of electronic structure calculations / 71.15.Mb – Density functional theory, local density approximation, gradient and other corrections / 71.20.-b – Electron density of states and band structure of crystalline solids / 71.15.Dx – Computational methodology (Brillouin zone sampling, iterative diagonalization, pseudopotential construction)
© EDP Sciences, Società Italiana di Fisica, Springer-Verlag, 2008