Phase Transformation and Superstructure Formation in (Ti0.5, Mg0.5)N Thin Films through High-Temperature Annealing

Abstract

(Ti0.5, Mg0.5)N thin films were synthesized by reactive dc magnetron sputtering from elemental targets onto c-cut sapphire substrates. Characterization by θ–2θ X-ray diffraction and pole figure measurements shows a rock-salt cubic structure with (111)-oriented growth and a twin-domain structure. The films exhibit an electrical resistivity of 150 mΩ·cm, as measured by four-point-probe, and a Seebeck coefficient of −25 µV/K. It is shown that high temperature (~800 °C) annealing in a nitrogen atmosphere leads to the formation of a cubic LiTiO2-type superstructure as seen by high-resolution scanning transmission electron microscopy. The corresponding phase formation is possibly influenced by oxygen contamination present in the as-deposited films resulting in a cubic superstructure. Density functional theory calculations utilizing the generalized gradient approximation (GGA) functionals show that the LiTiO2-type TiMgN2 structure has a 0.07 eV direct bandgap.

Experimental Synthesis of Theoretically Predicted Multivalent Ternary Nitride Materials

“…177 Another paper from the same group reported an ∼100× increase in electrical resistivity from ∼10 to ∼3200 μOhm cm with measured optical absorption minima in the 1.7−2.0 eV range for (Mg x Ti 1−x )N solid solutions, suggesting an extrapolated band gap of 0.7−1.7 eV for semiconducting Ti 0.5 Mg 0.5 N. 178 These experimental reports followed a computational prediction of thermodynamic stability, crystal structure, and electronic properties of MgTMN 2 (TM = Ti, Zr, Hf) compounds. 69,109 Phase transformations 179 and plasmonic properties 180 of the (Mg x Ti 1−x )N alloys have also been reported. Until recently, TMs in the highest oxidation stated had not been incorporated in Mg−TM−N compounds, but MgMoN 2 with a lowered Mo (+IV) oxidation state has been synthesized in bulk form.…”

Band Gap-Tunable (Mg, Zn)SnN2 Earth-Abundant Alloys with a Wurtzite Structure

“…Ti 1−x Mg x N with a rocksalt structure is a TiN-based nitride, which can be epitaxially grown on MgO(001) 63,64 and c-Al 2 O 3 . 65 The Ti 1−x Mg x N epilayers have been examined as a plasmonic material, and the unscreened plasma energy was tuned from 7.6 to 4.7 eV by increasing x from 0 to 0.49. 64 As described above, II−IV−N 2 and derived nitrides exhibit a variety of optoelectronic properties.…”