Electronic structure and lattice dynamics of CaxMg1−xS in the rock-salt phase

• Published in: Materials science in semiconductor processing Vol. 18; pp. 71 - 79
• Main Authors: Ghebouli, M.A., Choutri, H., Bouarissa, N.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01.02.2014; Elsevier
• Subjects: Ab initio calculations; Alloying; Alloys; Band structure; Band structure of solids; CaxMg1−xS; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Electron states; Electronic structure and electrical properties of surfaces, interfaces, thin films and low-dimensional structures; Electronic structure of nanoscale materials : clusters, nanoparticles, nanotubes, and nanocrystals; Electronics; Energy gaps (solid state); Exact sciences and technology; Lattice dynamics; Lattices; Mathematical analysis; Methods of electronic structure calculations; Optical constants: refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity; Optical properties and condensed-matter spectroscopy and other interactions of matter with particles and radiation; Optical properties of bulk materials and thin films; Phonon states and bands, normal modes, and phonon dispersion; Phonons and vibrations in crystal lattices; Physics; Rock-salt phase; Semiconductors; Band structure; Ab initio calculations; Rock-salt phase; Lattice dynamics; CaxMg1−xS; Conduction bands; Semiconductor materials; Dynamic properties; Lattice parameters; Optical measurement; Energy gap; Electronic structure; Quantity ratio; Reflection spectrum; S; Phonon mode; Alloying; Generalized gradient approximation; Mg; Absorption spectra; Optical absorption; Bulk modulus; Optical spectrum; Ca
• ISSN: 1369-8001; 1873-4081
• DOI: 10.1016/j.mssp.2013.10.029

Electronic band structure and lattice dynamical properties of CaxMg1−xS alloys in the rock-salt phase have been investigated. The calculations are performed in the framework of ab initio pseudo-potential approach within the generalized gradient approximation. Reasonable agreement is generally obtained between our results and the available experimental observations and previous calculations. The deviation of the alloy lattice constant and bulk modulus from linearity has been examined and discussed. Fundamental band gaps and Г–X and Г–L separations in higher-lying conduction bands are predicted. In agreement with reflectivity spectrum and recent optical absorption spectrum measurements, CaS in the rock-salt phase is found to be an indirect band-gap (Г–X). Similarly to CaS, the electronic band structure calculations showed that MgS is also an indirect band-gap (Г–X) semiconductor. However, a system transition between indirect and direct structures has been predicted in the Ca concentration range 0.12–0.83. Upon alloying the phonon modes are significantly changed showing that the longitudinal optical–transverse optical (LO–TO) splitting becomes narrower as one proceeds from pure rock-salt MgS to pure rock-salt CaS.