Physical properties of epitaxial ZrN/MgO(001) layers grown by reactive magnetron sputtering

• Single-crystal ZrN films, 830 nm thick, are grown on MgO(001) at 450 degrees C by magnetically unbalanced reactive magnetron sputtering. The combination of high-resolution x-ray diffraction reciprocal lattice maps, high-resolution cross-sectional transmission electron microscopy, and selected-area electron diffraction shows that ZrN grows epitaxially on MgO(001) with a cube-on-cube orientational relationship, (001)(ZrN)parallel to(001)(MgO) and [100](ZrN)parallel to[100](MgO). The layers are essentially fully relaxed with a lattice parameter of 0.4575 nm, in good agreement with reported results for bulk ZrN crystals. X-ray reflectivity results reveal that the films are completely dense with smooth surfaces (roughness = 1.3 nm, consistent with atomic-force microscopy analyses). Based on temperature-dependent electronic transport measurements, epitaxial ZrN/MgO(001) layers have a room-temperature resistivity rho(300K) of 12.0 mu Omega-cm, a temperature coefficient of resistivity between 100 and 300K of 5.6 x 10(-8) Omega-cm K-1, a residual resistivity rho(o) below 30K of 0.78 mu Omega-cm (corresponding to a residual resistivity ratio rho(300K)/rho(15K) = 15), and the layers exhibit a superconducting transition temperature of 10.4 K. The relatively high residual resistivity ratio, combined with long in-plane and out-of-plane x-ray coherence lengths, xi(parallel to) = 18 nm and xi(perpendicular to) = 161 nm, indicates high crystalline quality with low mosaicity. The reflectance of ZrN(001), as determined by variable-angle spectroscopic ellipsometry, decreases slowly from 95% at 1 eV to 90% at 2 eV with a reflectance edge at 3.04 eV. Interband transitions dominate the dielectric response above 2 eV. The ZrN(001) nanoindentation hardness and modulus are 22.7 +/- 1.7 and 450 +/- 25 GPa.

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