Growth and properties of epitaxial Ti1−xMgxN(001) layers

Abstract

Epitaxial Ti1−xMgxN(001) layers were deposited on MgO(001) by reactive magnetron cosputtering from titanium and magnesium targets in 15 mTorr pure N2 at 600 °C. X-ray diffraction (XRD) indicates a solid solution rock-salt phase for the composition range x = 0–0.55, a lattice constant that increases monotonously from 4.251 Å for TiN to 4.288 Å for Ti0.45Mg0.55N, and a decreasing crystalline quality with increasing Mg content, as quantified by the XRD ω rocking curve width which increases from 0.25° to 0.80°. XRD φ-scans show that all Ti1−xMgxN layers with x ≤ 0.55 are single crystals with a cube-on-cube epitaxial relationship with the substrate: (001)TiMgN║(001)MgO and [100]TiMgN║[100]MgO. In contrast, a larger Mg concentration (x = 0.85) leads to a polycrystalline, phase-segregated, nitrogen-deficient microstructure. The room temperature electrical resistivity increases from 14 μΩ cm for x = 0 to 554 and 3197 μΩ cm for x = 0.37 and 0.49, respectively. Ti1−xMgxN layers with 0.49 ≤ x ≤ 0.55 exhibit a negative temperature coefficient of resistivity which is attributed to the decreasing electron density of states at the Fermi level and a weak carrier localization. Optical transmission and reflection measurements indicate a decreasing electron density with increasing x and absorption minima at 2.0 and 1.7 eV for Ti0.63Mg0.37N and Ti0.48Mg0.52N, respectively, suggesting an extrapolated bandgap for semiconducting Ti0.5Mg0.5N of 0.7–1.7 eV.