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Abstract New materials that exhibit strong second-order optical nonlinearities at a desired operational frequency are of paramount importance for nonlinear optics. Giant second-order susceptibilityχ⁽²⁾has been obtained in semiconductor quantum wells (QWs). Unfortunately, the limited confining potential in semiconductor QWs causes formidable challenges in scaling such a scheme to the visible/near-infrared (NIR) frequencies for more vital nonlinear-optic applications. Here, we introduce a metal/dielectric heterostructured platform, i.e., TiN/Al₂O₃epitaxial multilayers, to overcome that limitation. This platform has an extremely highχ⁽²⁾of approximately 1500 pm/V at NIR frequencies. By combining the aforementioned heterostructure with the large electric field enhancement afforded by a nanostructured metasurface, the power efficiency of second harmonic generation (SHG) achieved 10⁻⁴at an incident pulse intensity of 10 GW/cm², which is an improvement of several orders of magnitude compared to that of previous demonstrations from nonlinear surfaces at similar frequencies. The proposed quantum-engineered heterostructures enable efficient wave mixing at visible/NIR frequencies into ultracompact nonlinear optical devices. 

Recently, the application of transition metal mononitrides (TMNs) to plasmonics and nonlinear optics has grown at an astounding rate. TiN and ZrN have emerged as the dominating materials in this direction. However, even though ZrN is reported to have lower dielectric losses and enhanced tunability in plasmonic applications when compared with TiN, the body of work regarding TiN is much more mature than that of ZrN. This imbalance of work regarding ZrN may be in part an effect of pollution in precursor materials for the fabrication of ZrN, leading to an increased imaginary part of permittivity and frustration in reproduction of ZrN with literature‐like properties. Herein, the effects of Hf defects (a common pollutant in Zr) on the optical properties of nitride films grown with radio frequency (RF) magnetron sputtering are reported. Hf defects are introduced into nitride films with a sputtering target made of the Hf‐polluted “grade 702” Zr alloy. Hf defects are found in all analyzed films with concentrations at around ≈0.5−1 at %. Chemical, structural, and optical properties of RF magnetron‐sputtered Hf_x:Zr_yN_zfilms (x ≪ y,z) are characterized and discussed.