Microstrain and defects in polycrystalline Zn_{1-x}Mg_{x}O (0 <= x <= 0.15) studied by X-ray diffraction, and optical and Raman spectroscopies

Abstract

The properties of polycrystalline wurtzite Zn_{1-x}Mg_{x}O (0 <= x <= 0.15) have been studied, by powder X-ray diffraction, including an analysis of the X-ray line-broadening, and by luminescence, absorption, and Raman spectroscopies. We have previously established from synchrotron X-ray difffraction that with increasing Mg-concentration, the c-axis compresses, and the off-center cation displacement within each tetrahedral (Zn,Mg)O_{4} unit decreases. Here we perform a size-strain line-broadening analysis of the XRD peaks, which reveals that the Mg-substitution reduces the coherent crystallite size and also develops the lattice microstrain. The optical properties of the samples have been characterized by diffuse-reflectance spectroscopy and fluorimetry. Both the optical band gap and the band-edge emission energies gradually increase with the Mg-concentration in Zn_{1-x}Mg_{x}O. The Mg-substituted samples show broader band tails near the absorption edge, due to the increase of crystal imperfections. The peak broadening of the E_{2}{high} Raman mode, upon the Mg-substitution, is also ascribed to the phonon shortening lifetime mechanism via crystal defects.