Defect-controlled electrical and optical properties of CrN thin films: experiment and first-principles study
Thin chromium nitride (CrN) films were deposited by RF magnetron sputtering in a reactive atmosphere of Ar-N$_2$ on fused silica and MgO (001) substrates at temperatures between 400 $^o$C and 800 $^o$C. The influence of nitrogen content and substrate temperature on structural, electrical, and optical properties was systematically investigated. The overstoichiometric CrN films exhibited a reduced resistivity below 6 m$Ω\cdot$cm with stable p-type behavior, while increasing the substrate temperature above 600 $^o$C induced a transition to n-type conductivity. Spectroscopic ellipsometry in the UV-Vis-NIR and infrared spectral ranges revealed a strong dependence of the dielectric function and the absorption edge on film stoichiometry and deposition conditions. Structural characterization using X-ray diffraction and atomic force microscopy confirmed substrate-dependent crystallinity and grain growth. Density functional theory calculations showed that cation and anion vacancies strongly modify the electronic structure and optical response, explaining the experimentally observed conductivity transitions. The results demonstrate that the deposition parameters provide an effective means to tailor CrN thin films via defect engineering.