Growth of aluminum nitride on a silicon nitride substrate for hybrid photonic circuits

Aluminum nitride (AlN) is an emerging material for integrated quantum photonics with its excellent linear and nonlinear optical properties. In particular, its second-order nonlinear susceptibility $\chi^{(2)}$ allows single-photon generation. We have grown AlN thin films on silicon nitride via reactive DC magnetron sputtering. The thin films have been characterized using X-ray diffraction, optical reflectometry, atomic force microscopy, and scanning electron microscopy. The crystalline properties of the thin films have been improved by optimizing the nitrogen to argon ratio and the magnetron DC power of the deposition process. X-ray diffraction measurements confirm the fabrication of high-quality c-axis oriented thin films with a full width at half maximum of the rocking curves of 3.9 deg. for 300-nm-thick films. Atomic force microscopy measurements reveal a root mean square surface roughness below 1 nm. The AlN deposition on SiN allows us to fabricate hybrid photonic circuits with a new approach that avoids the challenging patterning of AlN.