A new semiconductor: Ti0.5Mg0.5N(001)

Ti_0.5Mg_0.5N has recently been predicted to be a semiconductor with a 1.3 eV band gap and promising properties for thermoelectric and plasmonic devices. As a first step towards experimental validation, epitaxial Ti_0.5Mg_0.5N(001) layers are deposited on MgO(001) by reactive magnetron co-sputtering from titanium and magnesium targets at 600 °C in pure N₂ atmospheres. X-ray diffraction ω-2θ scans, ω-rocking curves, φ-scans, and high resolution reciprocal space maps show that Ti_0.5Mg_0.5N alloys form a pseudobinary rocksalt structure and are single crystals with a cube-on-cube epitaxial relationship with the substrate: (001)_TiMgN || (001)_MgO and [100]_TiMgN || [100]_MgO. A 275-nm-thick Ti_0.5Mg_0.5N layer is fully relaxed and exhibits a 002 ω-rocking curve width Γ_ω = 0.73°, while a 36-nm-thick layer is fully strained and has a Γ_ω = 0.49°. These results indicate a thickness-dependent strain state which suggests a critical thickness for misfit dislocation nucleation and glide which is between 36 and 275 nm. A measured negative temperature coefficient of resistivity in combination with a low optical absorption coefficient of 0.25 × 10⁵ cm^-1 for λ = 740 nm, and a vanishing density of states at the Fermi level measured by X-ray photoelectron spectroscopy support the prediction that Ti_0.5Mg_0.5N is a semiconductor.